5980-2090E

Agilent Technologiesand Communications:

Six Decades ofMeasurement Contributions

Agilent TechnologiesMarch 2000 Issue 20U.S. Edition

Contents

3 Agilent Technologies and Communications: Six Decades of Measurement Contributions

4 The early days

5 Cable multiplex communications

6 Pulse-coded modulation

7 Logic test and the digital revolution

8 Datacom testing

9 Digital transmission testers

10 Broadband communications

11 Terrestrial microwave communications

13 Satellite communications

15 Mobile-radio communications

16 Modern wireless communications

17 LMDS in the last mile

18 Military communications

21 Environmental testing

22 Broadcast communications

24 Cable television

25 Lightwave communications

27 RF and microwave component design

30 General communications applications

31 General technology contributions

33 Superstars

36 Agilent’s products today

2 Agilent Technologies and communications

3

It can be reasonably argued thatAgilent Technologies—which incor-porates the former test and mea-surement sector of Hewlett-PackardCompany—has been making measurement contributions to the communications industry ever sinceDave Packard and Bill Hewlettassembled their first product, an audio oscillator, in 1939 in aPalo Alto, California, garage.

That product was the HP 200Aaudio oscillator, and its mostfamous sale was to the Walt DisneyCompany for use in making themovie Fantasia. But it also wasused widely in the design of trans-mission components, includingamplifiers, transformers, and fil-ters, for the twisted-pair wirelinetelephony systems of that era.

With the outbreak of World War II,communications technology becamethe focus of intense R&D efforts as a strategy for winning the war. The results of those efforts revolu-tionized the world. Agilent, throughits HP heritage, has played a signifi-cant and continuing role in the communications revolution, makinghundreds of test and measurementcontributions in nearly every sectorof the industry.

In this document, we’ll take ajourney through the development of20th century communications andAgilent’s test and measurement contributions. Although we discusstechnologies up to the end of thecentury, our focus is on the histori-cal achievements rather than pre-sent-day trends.

Agilent Technologies and Communications: Six Decades of Measurement Contributions

Bill Hewlett and Dave Packard.


In the earliest analog telephonetechnology, open-wire telephonelines dominated the outside plant.Then came twisted-pair wires bundled into underground cables. In the U.S., these formed the back-bone of the communications systemwell into the 1940s. Some of us stillhave images of telephone polesalong country roads, with multiplecross-arms and dozens of green-glassinsulators supporting open wiresthat went on for hundreds of miles.The technology of communicating in those days was heroic, and itseemed that the only way to letmore people communicate wasthrough brute force design, byadding more wires over head ormore cables under ground.

Hewlett-Packard’s original audiooscillator, used with the 400A vacuum tube voltmeter (ca. 1941)that boasted a 1 megacycle band-width, allowed the characterizationof frequency-response parameters ofa variety of system components,including amplifiers, transformers,filters, line-loading components, and switches. One of Hewlett andPackard’s objectives was to provide“inexpensive quality,” and the audiooscillator was a good example.Originally advertised for $71.50 inthe Institute of Radio Engineer’s

Proceedings of1939, the oscilla-tor caught theattention of theChief Engineer atWalt DisneyCompany, whoneeded a numberof audio sourcesfor sound effectsin Fantasia. Thecompeting oscilla-tor of the day wasa “beat-frequency”oscillator that costten times as much. Disney’s ChiefEngineer bought eight of the HP models.

The clever circuitry of the 200Aaudio oscillator was the subject of Bill Hewlett’s ElectronicEngineering thesis at StanfordUniversity. In a slim document ofless than 20 pages, he presented a circuitry that was the essence ofsimplicity. It used a tunable resis-tance-capacitance network to pro-vide the 180-degree feedback phaseshift needed for oscillation; an inex-pensive tunable radio capacitor forthe two ganged capacitors; switchedresistors to achieve the tuningrange; and an innovative amplitude-stabilizing function made by insert-ing a positive-coefficient resistance—

a common 7.5 watt lamp bulb—intothe cathode circuit of the oscillatorvacuum tube.

With the introduction of the 300Aaudio analyzer (ca. 1941), engineerscould analyze signal distortion inthe audio components used in tele-phony. Testing was still in its earlydays. One HP engineer recalled as a college student being assigned toarrive at the engineering lab early in the morning to turn on the instrument so that its vacuum-tubedrift would stabilize for lab use later in the day.

In the telecommunications infra-structure, the underground wire-pairplant served local distribution needsfor decades, and HP continued tointroduce new test products toimprove its efficiency. In 1959, the302A wave analyzer (20 Hz – 50 kHz)brought powerful low-frequency (LF)spectrum analysis to component andsignal design. This analyzer was justthe second HP product with an all-transistor design—the first being1958’s 721A power supply.

In 1962, HP introduced the 3550Aportable frequency response test setfor installation qualification andtroubleshooting of twisted paircables. This product was followedby the 3555A telephone test set.These instruments were calledTransmission Measuring Sets (TMS),distinguishing them from the famil-iar Transmission ImpairmentMeasuring Sets (TIMS) of today.

The 200A audio oscillator was Hewlett-Packard’s first commercial success.

The 3550A frequency response test set could qualify and troubleshoot twisted-pair cables.

The early days

5

As the 1940s’ wireline technologyreached its limits, particularly in theunderground cabling of twisted pairsof wires that served urban areas,new technology was needed. Oneanswer was to exploit the broadbandcarrying capacity of coaxial cable,and as a result, AT&T’s research labsrolled out their first cable multiplexsystems, the L-1 through L-5.

Cable multiplexing grouped dozens of individual telephone conversationstogether using a technology called frequency domain multiplex (FDM).Each conversation occupied 3 kHz ofchannel width and was spaced 1 kHzfrom its neighbors. Twelve audio chan-nels were single-sideband-modulatedinto a group; five groups were com-bined to form a super group; and tensuper groups were combined into amaster group. The key to this technol-ogy was perfect linearity in the ampli-fication and all other circuitry. Slightnon-linearities showed up as inter-modulation, which resulted in degrad-ed background noise and cross-talk.

Amplitude flatness across the manymultiplexed channels was measuredover the 1.5 MHz band by HP’s 310Awave analyzer (ca. 1963). A waveanalyzer is essentially a calibratedsuperheterodyne receiver, and thisone featured a selectable outputbandwidth, which allowed the detect-ed audio modulation to be measured.

As cable multiplex technology progressed, AT&T added more andbroader channels to their cables,pushing the technology to its limitsby installing an underground cablesystem across the U.S. from NewYork to Los Angeles. Cable systemsalso began to provide the broadbandlinks required between the 7000 telephone central offices around the country. The AT&T L-systemsultimately reached 65 MHz per cable.

The 312A wave analyzer (ca. 1966)was a powerful diagnostic tool formultiplexed cable because it cov-ered the 18 MHz range, was fullyprogrammable, and featured manyuser improvements such as automaticfrequency control. Outside the U.S.,

the 3745A selective level measuringset (ca. 1975) offered system engi-neers following the CCITT-standardsprecise measurements of FDM tele-phone equipment with as many as3600 channels. This 25 MHz super-heterodyne receiver measured downas low as -125 dBm with synthesizerprecision. In 1978, the 90 MHz3747A selective level measuring set was targeted at the new genera-tion of 60 MHz cable that handled13,000 channels.

The 3586A/B/C selective levelmeters followed in 1980 for FDMapplications to 32.5 MHz. And com-panion 3336A/B/C synthesizer/levelgenerators teamed with the selectivelevel meter products to characterizetransmission components for both North American and CCITTsignal formats.

Cable multiplex communications

The 312A wave analyzer and 313A trackingoscillator were diagnostic tools for multi-plexed cable.


In a real sense, most of the spectac-ular communication technologies ofthe late 20th century were based ona simple analog-to-digital concept.In the 1960s, when it became eco-nomically and technically feasibleto digitize analog waveforms on amassive scale, everything in com-munications got better. Using awell-known sampling theory and an8-bit digital word to express ampli-tude samples taken at 8 kHz, each 3 kHz audio voice bandwidth wasconverted into a 64 kb/s digital datastream. Twenty-four streams wereinterleaved into the 1.544 Mbit/ssignal called T-1 in the U.S. Thismodulation format was described as time-division multiplex (TDM).

Amazingly, this T-1 signal could betransmitted on those same ordinarytwisted pairs, which vastly increasedcapacity without laying a single foot ofadditional cabling beneath the streets.

Now AT&T developed their T-systems,with a hierarchy of data rates up to T-4 (274 Mbit/s), running over coaxialcable. Similar standards were devel-oped outside the U.S., where theCCITT hierarchy packed 30 voicechannels into a 2.048 Mbit stream.

The digital data streams revolution-ized telephone voice quality. Astransmission distances hadincreased, the analog signals weresubject to gradually increasingnoise. When amplifiers were used tobuild up the analog signal for anoth-er cable hop, they added noise ineach hop. In contrast, digital pulseregeneration sent brand new pulsesinto the next cable hop, eliminatingthe audio noise and distortion thatcame with distance. So the low noiseand clarity we often attribute tofiber optics in reality began with thefirst digital technology of the 1960s.

HP’s digital instrumentation devel-oped across a broad front to helpspeed the digital revolution. The4940A transmission impairmentmeasuring set (ca. 1974) met anurgent need as telephone companiesbegan widespread installation ofdata modems to send data overvoice circuits. This TIMS wasdesigned to measure the analogparameters of wire lines that affectdata transmission, and it was usedwidely as a verification tool for linequality and performance testing.The 3770A amplitude/delay analyzermade similar measurements forCCITT standards.

Pulse-coded modulation

7

It wasn’t long after time-divi-sion multiplexing invaded theanalog domain that computer-to-computer data communica-tions arrived with a majordemand for transmissionbandwidth. The term datacomfirst came into use to definesuch computer-data traffic.PCM technology became themodulation format of choicefor serial data on cable and fordigital radio in terrestrial andsatellite applications. Digitaltechniques began to influenceevery facet of communicationstechnology. And underpinningthis new datacom technologywere logic circuits.

Logic designers looked fordiagnostic measuring tools tohelp characterize their newdigital circuits. HP, with itslarge engineering departments,quickly became a pioneer—not onlyby developing new techniques, but by having an immediate forum inwhich to try out bright new ideas.Bill Hewlett coined the term “next-bench-syndrome” to describe how aproduct idea could gain quick accep-tance when neighboring engineersimmediately asked to borrow theinventor’s new measurement tool.

The concepts of logic test startedsmall. The 10525A logic probe (ca. 1969) traced logic states in TTLand DTL integrated circuits with asimple probe tip and associated LEDindicator. The 10528A logic clip (ca. 1970) and 10529A logic com-parator were little, handheld diag-nostic tools that simply clipped ontoIC packages and gave the user imme-diate feedback through an array ofLED lights.

Complete instruments were soon onthe way. The 5000A logic analyzer(ca. 1973) featured a two-line dis-play of 32 LEDs, each of which cap-tured a pulse stream and displayedthe pulse sequence. The instrumentwas a sort of specialized oscilloscopewith sophisticated pulse condition-ing and capture processes.

Next the 1600L logic state analyzer(ca. 1974) was built into an oscillo-scope configuration that displayed 16 consecutive logic states of 12-bitwords. This instrument had complextriggering modes for capturing specif-ic sequences of pulses from ICs andROMs. The 1645A data error analyzerthat followed analyzed bit error ratesand other transmission parameters.

The 1600A logic state analyzer (ca. 1975) was able to analyze 32data streams at 20 MHz. Its innova-tive “data-map” display could locatedigital words on a two-dimensionalmap, which also displayed a vectorfor tracing the digital direction fromword to word. An associated multi-channel word generator, the 8016Aword generator, supplied 32-bitwords at 50 MHz. Such instrumentswere invaluable in the fast-movingworld of microprocessor development.

In 1973, HP introduced one of theearliest high-speed bit-error-ratetesters, consisting of the 3760A datagenerator and the 3761A error detec-tor. By stimulating circuits undertest using pseudo-random pulsesequences selectable from 7- to 32K-bit lengths, the system operated withbit rates up to 150 Mb/s.

The later 71603/612A Gb/stesters analyzed data-errorperformance all the way to12 Gb/s, and are used todayby many laboratories aroundthe world for developinghigh-speed optical transmis-sion systems.

In 1980, with the introduc-tion of the 64000-series logicdevelopment systems,design engineers began totake control of the burgeon-ing field of complex logicdesign for microprocessors.Then came tools to simulateVLSI circuit design andgraphical aids to providebetter insight into layoutprocesses.

More recently, HP/Agilentlogic analysis and emulation

tools are almost too numerous tolist, ranging from PC-hosted to high-ly integrated units with basic timinganalysis to cross-domain measure-ments. Hardware solutions are inte-grated with software solutions formicroprocessor and bus support.

HP/Agilent semiconductor test systems have also contributed in thisarea, by providing fast and compre-hensive characterization for VLSI,digital, memory/logic, mixed-signalRF, and semiconductor parametricapplications. These systems use pow-erful software and modeling routinesto speed the design iterations of those chip engineers in the communi-cations industry who must deal with rapid deployment and fast turnaround of design cycles.

Logic test and the digital revolution

An emulator for the Motorola 146805G2 microcomputer added newcapability to HP’s 64000 logic development system.


Over the years, an important general-purpose instrument for digital communications has been the pulsegenerator. HP introduced the 8015and 8011A pulse generators in 1973and 1974. These were followed by the8016A word generator of 1975, whichsupplied 8 simultaneous 32-bit wordsat 50 MHz for communications appli-cations. In the following decades, HPintroduced ever-higher data ratesand complex pulse formats for mea-surement and diagnostic applica-tions. On datacom R&D benches andproduction lines, pulse generatorshave served with the same impor-tance and ubiquity as oscilloscopes.

After system engineers tested the serialdata transmission—to ensure that pulselevels, data rates, and backup logictechniques such as parity and redun-dancy bits were getting to their desti-nations—they turned to the next-higherlevel of moving messages, the protocollevel. There, they needed to make surethat the handshake, start-message, endmessage, and all transmission “rules”took place in the right order.

Protocol analysis firstappeared about 1984,with the 4951/53/55Aprotocol analyzers. Datacommunication was get-ting to be serious busi-ness, and these instru-ments were designed toassist digital networkdesigners, data centers,and field maintenanceorganizations. Theywere powerfulmachines, covering themajor protocols of theday: X.25, HDLC, BSC,SDLC, SNA, DDCMP,X.21, and CCITT No. 7.They featured highlyflexible triggering andspeeds to 72 kb/s.

The introduction of the 4972A LANprotocol analyzer in 1989 targetedEthernet and StarLAN networks,and the 4974S/A MAP protocol analyzer supported IEEE 802.4,802.2, ISO, ACSE, FTAM, and more. HP was able to contribute much to

datacom testing becauseit was itself a largeuser of the technolo-gies. Agilent today car-ries on that tradition.

A typical example of a product familytoday is the AgilentAdvisor, a modularprotocol analyzer thatprovides powerfuldiagnostic and analy-sis functions for testing multiple datatechnologies such asLAN, WAN, ATM, andemerging voice overIP (VoIP) and fax protocols. Agilent’sLAN Analyzer prod-uct family today pro-vides hardware andsoftware to manageand maintain10/100/1000 EthernetLANs and 4/16 TokenRing networks. The

family includes the company’s firstsoftware analyzer that runs on anotebook PC.

The emergence in the late 1980s ofthe CCITT No. 7 Common ChannelSignaling protocol (SS7) revolution-ized the control of message switch-ing. Earlier strategies called formessage routing information to besent down the same channel as thevoice or data, leading to fraudulentexploitation of the network by so-called “blue boxes,” which couldsimulate switching-control signals.By moving all message-routinginstructions onto a separate, dedicated channel, system opera-tors could centralize operationalcontrol of their networks. From thiscame a powerful ability to monitorand measure all kinds of signalingsystem parameters. The 37900A sig-naling test set (ca. 1989) helpedinstall and maintain these signalingsystems. And it led directly to theacceSS7 network monitoring system(described under Superstars) andthe current signaling advisor testsets, which non-intrusively monitorthe SS7 network, displaying real-timeanalysis of signaling data, loadinglevels, and error rates, and provid-ing statistical reports of messagetypes and more.

The 37900A signaling test set sped troubleshooting of SS7 networks.

Datacom testing

The portable Internet Advisor (now Agilent Advisor) introducedinternetworking test capability for LAN, WAN, and ATM networks.

9

Digital transmission testersThe fundamental measure of perfor-mance or quality in digital systemsis the probability of any transmittedbit being received in error. This isthe purpose of digital pattern gener-ators and error detectors, oftenreferred to as bit error rate testersor BERTs. HP’s long tradition ofoffering the highest performinginstruments in this class is carriedon by Agilent today.

The 86130A 3.6 Gb/s BitAlyzer is a serial BER tester with power erroranalysis capability and a friendlyuser interface. As described earlier,the 71612A error performance analyzer addresses digital testing to 12 Gb/s. The ParBERT 81250 parallelBER tester generates pseudo randomword sequences (PRWS) and standardPRBS on parallel lines up to 2.67 Gb/s,making it ideal for multiplexer anddemultiplexer testing. The E7580AProBER is a handheld tester for 2 Mb/sand 64 kb/s digital-circuit testing.

Beginning in the 1990s, HP’s SONETand SDH analyzers performed accurate, reliable tests on networkequipment and transmission services. Portable units were used to troubleshoot SONET and SDHequipment at rates up to 2.5 Mb/s.Modular, VXI-based instrumentationcould be easily integrated into R&D,production-line, or ATE systems for testing both SONET and SDHstandards up to 10 Gb/s.

Today the Agilent OmniBER familyof communications performanceanalyzers offers a range of one-box,field-portable testers for installation,maintenance, commissioning, andmanufacture of transport networksand network equipment. Optical1310nm and 1550nm interfaces are supported, as well as electricalinterfaces at all the commonly usedtelecom rates. The testers can beconfigured to include DSn, PDH,SDH, SONET, ATM, DWDM, and jitter generation and measurement.They perform non-instrusive moni-toring of live traffic or test networkprotection switching mechanisms,out-of-service BER measurements,and other important parametric tests.

The Agilent SpectralBER test solutions offer flexible and versatileSDH/SONET functional test capabili-ty from 155 Mb/s to 10 Gb/s.

With the acquisition of CERJAC, a manufacturer of portable telecom-munications test equipment, HPexpanded the breadth of its field-service test products in the early1990s. Portable and handheldinstruments for field-service testingincluded the CERJAC 156ATM testset as well as products for T-carriertesting. Those product lines haveevolved to the Agilent TelecomToolkit, which includes the modular,flexible Service Advisor portabletest tablet platform with a growingfamily of plug-in modules for ADSL,HDSL, ATM, SONET, SDH, PDH, andTDR testing; the portable T1 and E1 Advisor families, and the auroraseries of handheld testers for DSL,ISDN, frame relay, and ATM testers.

Agilent ‘s tablet-based Service Advisor, part of the Telecom Toolkit, reflects the industry’sincreasing desire for modular, handheld, multi-format test instruments.


The early 1990s saw the rise ofbroadband communications, whichhas been spurred by the phenome-nal growth of the Internet and the“fast packet” revolution. One of thefirst robust technologies developedto deliver high bandwidth serviceswas asynchronous transfer mode(ATM). HP was a leader in develop-ing ATM test technology, and theintroduction of the BroadbandSeries Test System (BSTS) in 1994quickly became the industry stan-dard for ATM testing. Today theBSTS continues to offer the indus-try’s most comprehensive solutionfor ATM Forum traffic managementcompliance and for ATM signalingtest. With the evolution of wire-speedswitch-routers from enterprise net-works to carrier data networks, the BSTS has expanded to includenew standards such as packet-over-SONET (POS). As ATM is a key tech-nology for multiplexing voice, data,and signaling between fixed networkelements, the BSTS added third-gen-eration (3G) wireless test capabilityin 1999 for testing new wireless data technology.

Broadband communications

The Broadband Series Test System has been the industry’s platform of choice for testing ATMtechnology since 1994.

11

In the early 1950s, AT&Texploited the earlier,wartime development of microwave signal sourcessuch as klystrons and beganinstalling a cross-countryradio link system known as the TD system, whichoperated in the 3.7 to 4.2 GHz band. A 30-MHzbandwidth was devoted toeach of the system’s FM-modulated channels, whichcarried 1800 (later 2700) conversations.

Soon microwave antenna towersbegan appearing on the flatlands ofnorthern Indiana and the mountain-tops of Nevada and California. Thesystem was extremely complex forthat time, since the coast-to-coastspan required perhaps 150 radioline-of-sight hops. Because the systemwas all analog, all its links operatedin series, thereby placing specifica-tions of unprecedented tightness onamplifier flatness, group delay, andintermodulation.

Microwave communication linksmoved into north-south systems, and one well-known link fromChicago to St. Louis became thefounding asset of MicrowaveCommunication Inc. (later MCI Corp.and now MCI WorldCom), the firstdirect competitor to industry-giantAT&T. Terrestrial microwave tech-nology was the first technical solu-tion for transmitting broadband signals nationwide, and it also helpedlaunch today’s network television.

To help microwave communicationcompanies install and maintain theirmicrowave radio links, HP developedthe 623/24A microwave test sets (ca. 1952), which offered three func-tions: supplied test power with cali-brated output to -100 dBm for test-ing the system receiver, power mea-surement of the system transmitter,and frequency measurement of thesystem transmitter. The test setswere available for the 4, 6, and later11-GHz communications bands.

As the technology progressed, one of the key instruments that measuredand verified amplitude flatness and tight group delay on system components was the 3702B/3710Amicrowave link analyzer (ca. 1972).By presenting the phase deviationsfrom linearity on an oscilloscope, the analyzer allowed designers andtechnicians to tune components and antennas into specification. The 3730A down converter and the8605A microwave upconverter wereused to translate the analyzer’s measurement capability into themicrowave carrier bands.

The 3792A microwave linkanalyzer (ca. 1975) andlater the 3711/12A IF/BBtransmitter/receiver (ca.1979) were able to handlesystems with intermediatefrequencies of 140 MHz,designed for 2700 telephonechannels. Such dense multi-plexing required precisecontrol of distortions suchas AM-to-PM conversionsand amplitude linearityand group delay.

After AT&T’s microwave link systemhad been in use for many years, the U.S. Federal CommunicationsCommission (FCC) allowed AT&T to relax earlier rules requiring 2 of the 12 channels to be reserved for “hot-standby.” AT&T instantlyincreased their channel capacity,and the only penalty was the need to install an HP 83001A agile micro-wave radio (ca. 1974) at each repeaterstation. The 83001A could be tuned to any of the operational channels, so it could replace an out-of-servicechannel during maintenance.

Terrestrial microwave communications

The 3708A gave engineers an accurate way to assess the performance ofmicrowave radio and satellite modem systems.


Since much of the circuitry ofmicrowave radio is analog, newdiagnostic equipment was neededwhen digital modulation formatsbegan to invade microwave radioapplications. The 3709A constella-tion display (ca. 1987) providedvaluable insights into commonlyused modulation formats such asQPSK, 9QPR, 16QAM, and 64QAM.The companion 3708A noise andinterference test set helped engi-neers quantify the all-important relationship betweensignal-to-noise and bit-error-rate.

In 1987, HP’s signal generatorsbegan to feature the complex digitalmodulation formats that were beingused by communication systemdesigners. The 8780A vector signalgenerator provided 150 Mb/s datarates for digital phase modulationssuch as BPSK, QPSK, and 16- and64-QAM at carrier frequencies up to3 GHz. This generator was the firstto accept data lines, rather thananalog signals, for modulation.

A companion analysis tool, the8980A vector analyzer, was able todisplay high-speed vector diagrams,magnitude-phase versus time, andconstellation diagrams. It also pre-sented time-domain eye diagrams ofcomplex, high-data-rate modulationsintended for terrestrial and satelliteapplications. The first users werestartled to see a 3-dimensionalimage of a digitally modulated datastream that looked like a spiralspring extending out of the CRT.

The 11736A I/Q Tutor (ca. 1986) wasa clever little computer-trainingmodel that taught the fundamentalsof digital microwave radio using aPC. The I/Q Tutor modeled a systemblock diagram from the audio on oneend to the audio on the other. Ateach of the diagram’s stages—analog-to-digital converter, map to I/Q, filtering, mix to IF, upconvert to RF,power amplifier to antenna, andback again to audio—the modelscrolled down to typical waveformsand eye diagrams, allowing users toset filter factors, data rates, modula-tion types, and signal-to-noise ratios.

Testing was essential for terrestrialradio links, which experience multi-path fading due to signal reflectionsfrom mountain and ground effects.The 11758T digital radio test system(ca. 1990) combined measurement of eight different test parameters, so that design engineers could verifythat their signal equalizers mini-mized fading, and so that installa-tion engineers could meet FCC qualification requirements. The system included a microwave spec-trum analyzer to create a powerfultest instrument.

13

In the 1960s, technical visionariessaw the potential for using satellitesto carry massive amounts of commu-nication traffic all around the globe.The first commercial applicationswere made by the ComsatCorporation, a U.S. business-and-government alliance that funded theearly technology. Designers had tomanage complex multiplexing tech-nology and achieve reliability oftheir systems in the harsh environ-ment of space. Since repair and ser-vice to an in-orbit bird was impossi-ble, the designers had to incorporatemulti-path and redundant circuitsand components.

These “switchboards in the sky”were so complex that they usheredin a new era of automated testinstrumentation. HP was there withthe 8540A automatic network ana-lyzer (circa 1969). Controlled by the2116A instrumentation computer,the system enabled assembly and all-up-around checkout tests of the com-

plex signal paths inside the satellite.The 8540A was based on the 8410Avector network analyzer (VAN),which we’ll describe later.

Signal-switching matrix switchesrouted signals to and from the satel-lite under test, and provided power-ful test routines and complex signaldata processing. Error correctionaccounted for cable losses and signaldegradation. Signal-stability perfor-mance had been a key ingredient ofsatellite payload design from thebeginning. Thus, synthesizer-stabi-lized generators became the technolo-gy of choice for transceiver designers.

In orbit, satellites needed to havetheir channels loaded properly,because the transponders were lin-ear systems. Signals needed to bedistributed evenly so that peakpower wouldn’t be distorted andcause intermodulation effects. The8580A automatic spectrum analyzer(ca. 1971) was perfect for such a job.

Consisting of anHP 2116A com-puter and an8552A or 8553A-type spectrumanalyzer, whichwas modified forcomputer controland programmedfor long-term sig-nal monitoring,the system couldgather data con-tinuously and aid in managingthe signal trafficin satellite communications.

Phase-lockingtechnology of themid-1960s led HPto develop newapplications forhigh-stability sig-nals by phase-locking the vener-able 608D VHFsignal generatorand converting it

to the 608F. By designing a varactorinto the oscillator circuit, the 8708Afrequency synchronizer (ca. 1966),with its crystal-controlled, phase-locked source, eliminated the driftand cleaned up the phase noise.

The 8660A/B synthesized signal gen-erator (ca.1971) was one of the firstexamples of totally integrated, indi-rect signal synthesis. The instrumenthad plug-ins for both modulationand output control, and it provided0.01 to 110 MHz, and later 2600 MHz,with excellent signal performance.

In the 1960s, the era of the U.S.Apollo Space Program, which suc-cessfully put men on the moon, com-munications technology did not havecomponents with the integrated cir-cuits and LSI and VLSI that we knowtoday. Yet a system such as the inte-grated S-band communications linkused in the big Saturn rockets pro-duced magnificent results. Here wasa system in the 2350 MHz band thatcarried the entire telemetry trafficused to monitor hundreds of parame-ters in the propulsion systems andthe operational subsystems; the voicetraffic to and from the crew; medicaltelemetry; and finally, the most excit-ing communications innovation ofall, the video cameras. These cam-eras put us earthbound viewers rightin the cockpit—and out on the lunarrover, the little “golf cart” that car-ried its own camera onto the moon’ssurface and brought the world alongwith it. With a fixed camera left atthe landing site, we were able to seethe final liftoff from the moon, whichrippled the American flag standingon its pole, a testament of that greatventure. HP’s signal generators andspectrum analyzers served in thedesign and test of those incrediblecommunications systems.

In later decades, NASA venturedinto interplanetary scientific travel.Unmanned spacecraft now could useexquisite integrated circuits for pow-erful functional control and mea-surement of the far solar planets.Cameras and scientific payloads

Satellite communications

The 8580A automatic spectrum analyzer gathered data for managing satellite communications.


gathered massive amounts of datafrom our solar neighbors andadvanced the world’s knowledge of the creation of the universe. Thesophisticated communications linksand the massive earth antennassuch as the Goldstone dish in theMojave Desert testified to an ongo-ing tradition of innovation. How fartechnology had advanced is illustrat-ed by the fact that the 300 footdiameter Goldstone receiver couldobtain useful data from received signals at levels as low as one pho-ton per square meter per second.

Indirect frequency synthesisbecame the main feature of futuresynthesized generators and sweep-ers. In 1977, the 8672A microwavesignal generator delivered 2 to 18GHz signals with 15 ms programma-ble carrier agility. This instrumentbecame the core of a wide variety ofautomated satellite test systems.

The 8673A microwave signal genera-tor (ca. 1983) produced 26 GHz testsignals. It was followed by a familyof synthesized microwave sweepersthat could serve as highly stablesources for network analyzers, whichrequired error corrections at specif-ic frequencies. In order to speed network measurements, these syn-thesized sweepers used a modifiedsweep called “lock-and-roll.” Nowtwo categories of product were nowavailable: synthesized signal gener-ators that could modulate signalsand sweep, and lock-and-roll sweep-ers that could be synthesized.

In the 1990s, the 83731/32B signalsources upgraded the performance of AM, FM, and pulse modulationwith excellent phase noise and har-monics to 20 GHz. Today, Agilent’s83550A millimeter-wave sources supply signal power in multiplewaveguide bands from 26 to 110 GHz.They are increasingly useful as mili-tary, satellite, and commercial appli-cations move above the traditionalmicrowave communications bands.

Site-surveillance applicationsbecame important when satelliteground stations were first planned.Because those systems had toreceive tiny signals from space,earthbound interference could notbe tolerated. The 8582A automaticspectrum analyzer (ca. 1980) wasideal for testing these systems.Outfitted with broadband antennas,this analyzer could sit in a mobilevan for days and weeks, monitoringthe local signals and other man-made electromagnetic interferenceand preparing statistical-occurrencedata packages.

The 8660B signal generator is an early example of the use of totally integrated, indirect signal synthesis.

15

By the time WWII began,mobile radio communicationstechnology had already pro-gressed and was typified byFM-modulated radio linksthat served the public andsome commercial sectors.The transceivers used forpolice, fire, and forestryapplications were bulky andcumbersome, but still effec-tive. Transceiver circuitryemployed vacuum tubes,which depended on B+ sup-ply voltages of perhaps 125Vdc, obtained through use ofa vibrating contact thatchopped the 6 Vdc auto bat-tery supply into a step-uptransformer and a high-voltage-recti-fier vacuum tube.

Exploiting WWII tactical radio tech-nology, postwar applications inmobile telephony grew rapidly, par-ticularly after the introduction of thetransistor in 1948. Low-voltage andrugged, transistorized devices quick-ly replaced the bulky vacuum tubetechnology. However, frequency-spectrum assignments severely limit-ed mobile phone users because onlyone subscriber could use each tele-phone channel at a time. Moreover,base stations were spaced quite farapart, significantly restricting fre-quency reuse.

Frequency counters, power meters,and signal generators were theinstruments of choice for designing,testing, and maintaining mobiletransceivers. The 803A impedancebridge (ca. 1950) featured a novelapplication of the slotted- line tech-nique that allowed a 500 MHz mea-surement range in a very compactdevice. This bridge and the 805Aslotted line (ca. 1951) were used forimpedance measurements on RF andantenna sections.

A variety of signal generators servedthe mobile FM market, including sev-eral models acquired by acquisitionof the Boonton Radio Company in1960. The 202H (Boonton) FM signalgenerator was widely used in pro-duction and service facilities. LaterAM-FM generators such as the 8654Bsignal generator (ca. 1976) and the8642A/B signal generator (ca. 1985)featured expanded precision, capa-bility, and programmability formobile test. The 8642 generatorswere notable because they used sur-face-acoustic-wave technology toimprove signal-to-noise performanceof the programmable oscillators,even over cavity-tuned models.

A brand new concept for RF volt-meters was introduced in 1966 whenthe 8405A vector voltmeter waslaunched. The use of impulse sam-pling technology (described later)made this voltmeter unique. Byapplying the technology to two inde-pendent but synchronous channels,both channels of RF voltage could bemeasured to 1000 MHz, and the phasedifference between the two could bemeasured, as well. This remarkablecapability offered the RF mobiledesign engineer new insights into RFprinted-circuitry performance.

By adding signal-separationdirection couplers or RFbridges, the meter could betransformed into a sweepingimpedance meter. This two-channel concept led directlyto development of the block-buster 18 GHz 8410A net-work analyzer, introduced in 1968. (We cover this in theSuperstars section.)

About 1977, HP began tofocus on all-round testing ofmobile transceivers. By com-bining a desktop computer,signal generator, counter,power meter, various modu-lation sources, power sup-

plies, and switching, the 8950Atransceiver test system was born. It provided all the signal and mea-surement capability necessary tocompletely characterize an FMmobile transceiver. Affectionatelycalled “Bigfoot,” it began to definetesting strategies for the rapidlygrowing manufacture of huge quanti-ties of mobile radios.

HP had traditionally supplied general-purpose instruments fortransceiver measurements. Butstarting in about 1979, the 8901Amodulation analyzer directly targeted the mobile transmitter test market. The analyzer was essentially a 1000 MHz, calibrated receiver thataccurately and precisely measuredthe AM, FM, and phase modulationof mobile transmitters.

By combining the 8901A with the 8662A microwave synthesizer (ca. 1962) and 8903A audio modula-tion analyzer (ca. 1980), along withsome signal switching, specializedtest systems such as the 8957S cellular radio test system (ca. 1985)were created.

Mobile-radio communications

Modular printed circuit boards could be inserted and removedfrom the 8405A vector voltmeter for RF performance testing.


By the 1980s, the frequency-spectrumoverload in mobile telephony wasbecoming obvious. And one dramaticsolution was waiting in the wings—theconcept of cellular frequency-reuse,which envisioned a dense populationof base stations at regular (cellular)intervals, and a complex control sys-tem that would “hand off” a travellingtransceiver as it moved from one basestation cell to another. The idea wasrevolutionary, but new microproces-sor technologies made it possible andeconomically viable.

We can only pity those early radiodesigners who had to create RF frontends for mobile radios that encoun-tered some of the worst signal degra-dation imaginable. The radio had tocapture and retain the base-station sig-nal, while a car, traveling at highspeed, exhibited a considerableDoppler effect in frequency shift. Atthe same time, multipath effectscaused by mountains, buildings, oratmospheric conditions might be caus-ing the signal strength to fade intoblack holes with 70 or 80 dB attenua-tion. Enter the 11752A multipath fad-ing generator (ca. 1985), which simu-lated up to six multipaths with indi-vidually programmable amplitudeeffects, all to stress-test the circuitry ofthe mobile radio’s signal processing.

In 1992, HP launched a family of com-pact, portable cellular test sets, manyof which are still in use today. The8920A RF communications test setcombined measurements of 22 instru-ments for transceiver testing of land-mobile and cellular applications.Variations were developed to meetnew system formats. The 8920DTfocused on digital systems such asPDC. The 8921A cell site test systemcovered cellular base station testing.Yet another system, the 8924C, target-ed CDMA. Test sets were customizedfor GSM/DCS/PCM applications, forDECT (Digital European CordlessTelecommunications), and even forpagers. Today, base station testing isaccomplished with the 8935 seriesbase station test sets for CDMA andTDMA technologies.

In recent years, the company hasfocused attention on the evolvingneeds of mobile manufacturers forcomplex test equipment customizedto exact modulation formats and sig-nal performance. Before that, equip-ment was designed primarily forgeneral-purpose use. But systemdesigners now want test equipmentthat anticipates sophisticated newtechnologies. As we can see from thethree dozen pages of wireless testequipment in the 2000 Test andMeasurement Catalog, Agilent haslearned this lesson well.

Mobile systems now evolve so quick-ly that the key to success is agility.Test equipment suppliers must bequick to respond to customer needs.So, for example, because spectrumanalyzers are often the most criticalpiece of test equipment on thedesign bench, the 8590-series spec-trum analyzers (ca. 1988) weregiven plug-in firmware “personali-ties,” each of which customized themeasuring routines to specific jobs.Numerous and inventive test rou-tines have been offered for testingcable and broadcast TV, noise figureor EMC, and a multitude of wirelessformats, including GSM, CT2-CAI,NADC-TDMA, ODC, DCS1800,DECT, CDMA, PHS, and microwave

digital radio. Today’s ESA seriesspectrum analyzers carry on thetrend with evolving personalitiesfor CDMA and GSM.

The ESG-series RF signal generators(ca. 1995) have provided flexible digi-tal modulation for an exceptionalrange of RF communication applica-tions to 4 GHz. These include GSM,CDMA, TDMA, DECT, EDGE, andbroadband I/Q modulation. In addi-tion, an internal arbitrary waveformgenerator can play back virtually anymathematically generated waveform—an amazing signal simulator in a tra-ditional RF signal generator package.

With the 8960 Series 10 wireless com-munications test set introduced in1999, mobile phone manufacturerscould achieve breakthrough speed thatcould improve test throughput by upto 300% in a system designed to testmultiple communications formats.

Today as third-generation (3G) andinterim 2.5G digital wireless stan-dards emerge, Agilent is launchingmanufacturing, field-service, andnetwork operations test systems tohelp ensure the performance andquality of the next generation ofwireless network equipment, digitalappliances, and services.

The 8935 series base station test sets were designed to operate under varying environmental conditions.

Modern wireless communications

17

In the late 1990s, the battle heatedup to deliver interactive, broadbandconnection to homes and businesses,and the industry began to considerwireless technology alternatives(“fixed wireless”). One of the newservice formats developed was theLocal Multipoint Distribution System(LMDS). Allotted frequency at 30 GHz, LMDS consisted of a cellulararrangement of hub base stationsthat connected to homes and busi-nesses using very small (8-inchdiameter), line-of-sight antennasspaced about every 2 to 4 miles. This arrangement bypassed all theheadaches of laying undergroundcable and required easily installedmodems at the customer premises.HP developed a two-way LMDS technology for broadband, interac-tive connections that was sold in1997 to Lucent Technologies.

LMDS in the last mile


With vast and far-flung operations,the world’s military forces relyheavily on tactical and strategiccommunications. Most countrieswant to develop the most highlysophisticated, high-performancecommunications technology possibleto assure success in their complexmilitary endeavors. And while themilitary certainly depends on largeamounts of commercial communica-tions capacity, in every decade themilitary has had unique needs thathave pushed communications tech-nology to the limit.

One of the earliest products devel-oped by HP during WWII was the100A secondary frequency standard(ca. 1941). This crystal-controlledoscillator had countdown circuits toprovide precision outputs to 100 kHzand was used in certifying transmit-ter frequencies. In those days, fre-quencies were often standardizedusing the “Lissajous” comparisonpattern on a cathode ray tube, whichplaced a standard frequency on thehorizontal deflection, and theunknown signal on the vertical. The500A frequency meter (100 kHz) of1941 used an analog meter dial.

A fellowship grant made to Al Bagley,a young graduate student atStanford University in 1948, led the development of HP’s frequencycounters. Hewlett and Packard per-sonally asked Bagley to study themeasurement needs of the nuclearphysics industry. From that studycame the requirements for a fasternuclear-pulse-counting technologythat could resolve two nuclearevents only 0.1 microsecond apart.Bagley determined that new, low-capacitance semiconductor diodesjust coming on the market mightallow faster digital circuitry. He builta prototype as part of the project—and asked for a job at HP. When hewas hired, he was asked to continuethe work.

Out of that work came the 520A highspeed decimal scaler, which was ableto condition very short nuclear puls-es occurring at up to 10 MHz, and todivide down by factors of 10 or 100.Sadly, the 520A had only minimalcommercial success. However,Hewlett envisioned a different measurement process, one that gatedthose scaled-down, high-speed pulses(using a selectable time base similar

to that of the 100Atime standard) intoa slower-speedaccumulator(counter). Thus thecommon frequencycounter was born.

Frequency coun-ters were a hugecommercial successand in greatdemand from the1950s onward.They were used inmeasuring every-thing from trans-mitter frequenciesto the accelerome-ters on which bal-listic missile guid-ance systems werebased. HP becamethe industry leaderin electronic count-

ing in the early 1950s with the 524Afrequency counter (ca. 1952), whichboasted a 0.01 cps to 10 “mc” mea-suring range. It was augmented withthe 512A frequency converter tomeasure to 100 MHz.

In 1954, plug-in downconverterswere added and introduced as the524B electronic counter, whichbecame an industry standard forsome years. Plug-ins eventually mea-sured to 18 GHz, after the introduc-tion of the step-recovery-junctiondiode. With this diode, HP’s designengineers could create a broad combof harmonic spectra from a crystal-stabilized frequency source in the200 MHz region. This down-conver-sion technology allowed convenientmeasurements to 18 GHz, a realaccomplishment at that time.

Development of the 5100A frequencysynthesizer (ca. 1964) came about inresponse to the U.S. Navy’s criticalneed for a fast-switching, direct syn-thesized, high resolution signalsource for secure communications.The product was a marvel of thetime, covering 0 to 50 MHz with aresolution of 0.01 Hz and crystal fre-quency stability of 1 part in 1010. Itssuccess launched HP into a long lineof direct synthesizers that becamefaster, wider in range, and more flex-ible. The 5105A frequency synthesiz-er, offering 500 MHz direct synthesis,followed in 1967.

HP’s first entry into the RF measure-ment sector was introduced in 1943.The Model A signal generator, a UHF(ultra-high-frequency) signal sourcewith a 500 to 1350 MHz range, used“lighthouse” vacuum tubes for theoscillator and power amplifier.Frequency adjustment was madethrough ganged, tunable cavities.

To fulfill a wartime government pur-chase order, HP developed somesophisticated manufacturingprocesses that served the companywell for decades. For example, thedesign of the Model A used move-able, contacting short-circuit

Military communications

The 524 frequency counter established HP as a leader in electronic counting.

19

“fingers” to provide the cavity reso-nance function for the oscillator.Those fingers were assembled andworked in with a careful burnishingprocess. This process smoothed the sliding metal surfaces so thatelectrical noise would not occur asan operator tuned the frequencyacross the band. The manufacturingprocess also ensured a long life forthe cavities despite the wear fromcontinuous movement.

A commercial version of the wartimeproduct, the 610A UHF signal gener-ator, was introduced in 1948. The612A UHF signal generator (ca. 1953)found applications in UHF television,which had been opened up for broad-cast communications at that time.

The early HP signal generators pro-vided user features that contributedto the company’s dominance of thesignal generator market for decades.These included direct readouts of thefrequency, amplitude, and modulationfunctions—a big advance in usability.Also, the instruments incorporatedmutual inductance coupling andwaveguide-beyond-cutoff technology,which allowed precise attenuation ofthe output signal down to extremelylow levels, on the order of 1 microvolt.

Klystron tubes were the powersources of early HP microwave sig-

nal generators, and the first was the616A signal generator (1.8–4.2 GHz)of 1947. The 614-series signal gener-ators covered frequency bands to 21GHz and were replaced in 1962 withthe 8614/16 signal generators thatfeatured power leveling and ampli-tude modulation using PIN (positive-intrinsic-negative) diodes. PINdiodes made a significant contribu-tion to microwave amplitude con-trol. They were created by adding anintrinsic layer of silicon in the mid-dle of a standard PN junction. A PINdiode acted like a resistor at

microwave frequencies and a diodeat low frequencies, thus allowing theattenuation of an array of thesediodes positioned along a microwavetransmission line to be programmedwith a dc current.

It was not until 1982 that solid-stateYIG (yttrium-iron-garnet) sourceswere introduced in the 8683/84A signal generators, which covered the 2.3 to 12.4 GHz range withAM/FM/pulse modulation, makingthem suitable for many microwavecommunication applications.

Tactical aircraft communicationsand navigation systems have beencalibrated and maintained by a longline of signal generators, such as the450 MHz 608A VHF signal generator(ca. 1950). The 65 MHz 606A HF signal generator (ca. 1959) was well-suited for design and testing of theultra-long-range, single-sideband HFcommunications radios of the U.S.Strategic Air Command bombers.

Standard HP signal generatorshave served a variety of other mili-tary applications, such as tropos-pheric scatter communications, in which high power signals wereaimed at the horizon, and receiversover the horizon had to detect thetiny amounts of signal that scatteredfrom ionic elements in the high troposphere. The 606A high frequency signal generator could test ultra-long-range, high-frequency radios.

The 5100A frequency synthesizer answered the military’s need for a fast-switching, direct-synthe-sized, high-resolution signal source.


The 8640B VHF signal generator (ca. 1973) repre-sented a quantum leap insignal generation, replacingthe venerable 608-seriesgenerators that wereinstalled in thousands of radio test benches. To achieve superior phasenoise in the new product,the designers used a cavity-tuned oscillator to512 MHz. They phase-lockedthe oscillator for drift stabil-ity, and used a power doubler for 1024 MHz out-put. The digital countdowncircuits went to 500 kHz,and an internal frequencycounter gave user precision.The 8640B offered veryhigh-performance AM-FMsignals to military radiotesting for a decade.

As high-frequency digital circuitsbecame available, HP developed apowerful digital direct-synthesistechnology for use in secure commu-nications. The 8770A arbitrary wave-form synthsizer (AWS, ca. 1988) created completely arbitrary wave-forms from dc to 50 MHz by use of asuper-fast, digital-to-analog converter(DAC). This circuit could plot com-puted-amplitude points to createtotally arbitrary waveforms using 8 nanosecond-width pulses. HP’s frequency-agile technology also madeit possible to hop from one frequencyto another in the time it took to moveto a different sequence of 8 nanosec-ond pulses. More importantly, the

design was directly focused on signalgenerator performance standards,and the AWS far exceeded ordinaryfast (computer-style) DAC perfor-mance in signal-to-noise ratios andharmonic generation.

Next came fixed upconverters thatcould place the agile 50 MHz bandinto microwave application frequen-cies. Then in 1991, the 8791A fre-quency-agile signal simulator (FASS)added frequency-agile upconvertersthat achieved a typical 100 nanosec-ond agility all the way to 18 GHz. Inaddition to impressive carrier agility,FASS used a special waveform gen-eration language that allowed usersto program wide-bandwidth modula-

tions of arbitrary formatssuch as non-linear chirps,TDMA, and CDMA. Withsuch custom signals, oper-ating receivers could bestress-tested using actuallink traffic and congestedsignal environments testedwith in-channel and out-of-channel interference.

Some military satellitework, such as the MILSTARsatellite program, requiredultra-complex modulationsand frequency-agile for-mats to make them securefrom jamming and othermischief. Sophisticatedgenerators such as FASSand other millimeter-wavesignal source moduleswere introduced there.

Hybrid spectrum analyzer technolo-gy integrated frequency- and time-domain functions to process highlycomplex modulation signals for bothphase and amplitude information.These are typified by the 89410 to89450A vector signal analyzers (ca. 1993), which still offer unparal-leled capability, from baseband to10 MHz and from RF to 2650 MHz.Powerful signal processing softwarecontributes useful displays of digitalmodulation, statistical parameters,and advanced data analysis functions.Thus the analyzers can display timepatterns of digital modulation suchas eye-diagrams concurrently withphase patterns such as constellationand vector diagrams. Innovativewaterfall and spectogram displayformats give insight to communica-tion traffic characteristics.

The 8604B VHF signal generator featured built-in phase locking and a 550 MHz counter for high-performance AM and FM signal testing.

Vector signal analyzers such as the 89441A process highly complex,modulated signals to obtain both phase and amplitude information.

21

Products built for military communi-cations have influenced the commer-cial market in important ways. Forexample, a high standard of perfor-mance of HP and Agilent instrumentshas dramatically affected the owner-ship experience of the company’scustomers over the years. This performance standard was initiallythe result of HP’s so-called “Class B”environmental qualification.

In the early years, when HP occa-sionally contracted to design milita-rized test equipment for the ruggedfield conditions of the armed services,the operating requirements includeda wide range of thermal andmechanical stress. It was found, notsurprisingly, that when those instru-ments were later commercialized,their failure rate and field reliabilitywere often superior to many otherordinary designs.

This observation led HP to imple-ment an instrument class of envi-ronmental specifications that all HPcommercial products had to meet.Class B instruments had to operatefrom -40 to +65 degrees Celsius, andperform to specifications from 0 to+55 degrees C. During the designqualification of an instrument, theentire parts list was analyzed, partby part, to determine how much de-rating would be used. For example,resistors were to run at only 25% oftheir maximum published ratings.Since heat is generally the killer ofreliability, IR scans were made onchassis and printed circuit boardsto identify spots of unwanted heat.It is generally accepted that theserigid programs of operating qualifi-cations were fundamental in build-ing the high esteem held for HP andAgilent products.

Environmental testing


Certainly HP's early audio oscillatorsand distortion analyzers (such as the330B distortion analyzer, ca. 1941)found use in the broadcast industry,which in the 1940s meant simply AMradio broadcast. As frequency modu-lation technology was introduced tothe broadcast community, the FCCrequired instrumentation at thebroadcast station to continuouslymonitor the transmitter frequencyand the modulation characteristics. In1947, HP introduced the 335B broad-cast service monitor to meet theseFCC broadcast rules. Other broadcastmonitors followed, with the 335E TVwaveform monitor in 1945 and theimproved 337B FM monitor in 1950.

The early development of televisiontook place in the late 1930s and wasdemonstrated at the New YorkWorld's Fair in 1941, but implemen-tation was put aside during WWII.When postwar television rolled out,HP equipment was in demand for sig-nal simulation and analysis. The612A UHF signal generator (ca. 1953)became the signal source of choicebecause its modulation capabilitywas specifically designed for theUHF TV modulation formats. Thisproduct was a direct descendent ofthe 1943 Model A signal generator.

When HP entered the oscilloscopemarket in 1958, various specialtymarkets looked promising for thenew scope technology. In 1965, the191A TV waveform oscilloscope wasintroduced for broadcast studios totest the quality of the video signal.Some of HP’s oscilloscope innova-tions, including the internal gratic-ule for a more precise display and aflood gun for illuminating thescreen, were included in the 191A.This scope also featured higherbandwidth, so it could read and dis-play the VITS (vertical interval testsignal), which was a new test signaltransmitted during the TV verticalinterval period for concurrent moni-toring of signal distortions. Theseinnovations were important for theemerging color technology.

In the 1990s, video technologyunderwent a dramatic conversionfrom analog signal format to digital.The timing was right for many rea-sons: picture quality was higher,precision post-production editingwas available, dramatic improve-ments had been made in digital stor-age techniques, and reliability of thetechnology had improved over earli-er digital video tape. HP was confi-dent of the opportunities and creat-ed a division just to supply thebroadcast video market.

One of the first products was a novelframe-grabber-type video dataprocessor called the VidJet-Provideo print manager (ca. 1994). Itwas designed for broadcast andpost-production studios, which hadwalls full of video tape files. By pro-cessing video data from a streamingvideo signal, the VidJet could cap-ture a single video frame and createthe proper data map, which in turncould print the picture on a standardcolor page printer.

The VidJet provided other functions,such as detecting each scene changeand printing story boards with 30slide-sized thumbnail pictures on

the same sheet. In this way, videonews and other cassettes could beinventoried for easy access whenstudios needed to retrieve specificvideo clips. The product served animportant inventory function for afew years until replaced by on-linephoto shops.

Other products for the digital videomarket included a line of digitalvideo recorders and video servers.In 1993, HP introduced theMediaStream broadcast server. Thisproduct’s technology offered a dra-matic improvement in storage andplayback capability for broadcaststations and post-production stu-dios, first for 1 or 2 video channelsand later for up to 6 channels. Itoffered 50 hours of video storagefor advertising or spot media con-tent. Through integration with pro-gramming computers, it made digi-tal video instantly available, andthe new medium began to replacevideo tape and cart machines forplayback functions.

Video servers were more than justmodified computer data servers,because the video data had to beconstantly “streamed” to its applica-

The MediaStream broadcast server dramatically improved storage and playback capability forbroadcast television stations.

Broadcast communications

23

tions, and not subjected to the databursts typical of computer servers.HP made real contributions to theindustry with the development ofRAID (redundant array of indepen-dent disks) technology, which in thecase of a disk-element failureallowed reconstruction of the lostvideo from redundant data on othersurviving disks. Broadcast stationsmoved quickly to exploit the newdisk technology. HP supplied similardigital video storage with a line ofMediaStream disk recorders. Thesecould scale up to 5 channels withstorage capacity up to 18 hours.

In the test world, as analog videogave way to digital video technology,the 11759D dynamic ghost simulator(ca. 1993) stressed TV receivers withreal-life signal impairments such asairplane flutter, tower sway, andmountain or building multi-paths.The 8594Q QAM analyzer (ca. 1995)targeted performance testing of digi-tal video signals, including the 16,64, and 256 QAM formats used forsatellite distribution.

Data compression played an impor-tant role in the new digital videobroadcast. One standard, developedby the Motion Picture Experts

Group and called MPEG, became themain compression technology forrecording and playback of digitalvideo. The MPEG standard allowedeconomical data storage yet permit-ted editing functions and other

important broadcast and post-pro-duction processes. Today Agilent’sMPEGscope family of test products(ca. 1997) are used in the industryfor MPEG-2 as well as DVB (digitalvideo broadcast) and ATSC(Advanced Television StandardsCommittee) system developmentand qualification. The MPEGscopesare used to verify and debug digitalTV network systems, includingencoders, multiplexers/demultiplex-ers, set-top boxes, and video servers.In 1999, the MPEGScope was award-ed an Emmy for technical contribu-tions to the television industry.

The 8594Q QAM analyzer targeted performance testing of digital video signals.

In 1999 the MPEGscope won an Emmy award for technical contribution to the television industry.


HP was an early contributor to thecable industry, even in cable’s firstincarnation as community antennatelevision (CATV) in the late 1940s.Often tiny local companies werebuilt on a shoestring to bring broad-cast TV “over the mountain” wheredirect line-of-sight signals didn’treach. Some general-purpose HPgear was used in designing thebroadband amplifiers and circuitcomponents such as signal splittersand combiners. Certain transmis-sion testers that were used for tele-phony cable maintenance could beapplied to cable TV installation andservice, as well.

Powerful yet versatile signal testingfor the cable industry came about in1991 when the innovative 8591Ccable TV analyzer was introduced.This full-featured spectrum analyzeroperated a measurement personality(loaded from a plug-in card) thatdisplayed test parameters for videoand carrier characterization in theunits of the application. In the early1990s HP

acquired CaLan, a manufacturer ofcable test equipment, which added anew array products including asweep/ingress analyzer and signallevel meters.

In recent years, the cable industryhas faced intense competition fromother service providers, includingdirect satellite system (DSS) televi-

sion and telecommunications. Inresponse, cable operators began

evolving their businesses tosupply more than just pack-

aged entertainment. Theybegan to upgrade coaxial-based facilities withfiber-optic technologyand introduce digitalcommunication ser-vices—including highspeed Internet access,

telephony, data, andinteractive television.

HP—today as Agilent—hasaddressed the growing com-

plexity of cable systems with awide range of instruments in addi-

tion to the traditional cable TV testproducts. To help cable operators

turn up two-way systems, the compa-ny introduced in 1998 a return pathmonitoring and analysis system. Fortelephony and converged servicetesting, Agilent supplies protocolanalyzers with voice over IP testcapability and a voice quality tester.

Fiber testing can be performed witha mini OTDR, WDM channel analyz-er, and optical spectrum analyzer.Digital broadcast test equipment(described above) is also used. Anadvanced, automated test suite forDOCSIS verification was introducedin 1999 to assist in standard certifi-cation of new and important tech-nologies critical to the deploymentof interactive cable services.

Cable television

The 8591C cable TV analyzer was given a flexible hardware and software architecture that couldbe upgraded to keep pace with changing regulations.

Portable cable TV test products include the3010 series sweep/ingress analyzer.

25

The confluence of solid-state laserlight sources invented in the 1960sand the low-loss glass fibers devel-oped by Corning Glass Co. around1970 fostered a communicationsrevolution unmatched in human his-tory. The amounts of digitized voiceand data now transmitted by lightacross continents and under theoceans are so massive that even thegreatest visionaries cannot predictwhere the growth will end. And theproduction and installation of fiber-optic technologies continue to accel-erate. All these advancements haverequired the services of new kindsof test and measurement equipment,and fortunately HP was there.

The parade of innovative measure-ment solutions started simplyenough. As the first fiber-optic linkswere being developed, the fibershad generally high loss and werebest suited for short distances.Fiber inventors were willing to tryanything that could improve theirmeasurements. One engineerderived a simple fiber-power-sens-ing thermistor mount for HP’s regu-lar line of microwave power meters.The resulting 84801A fiber opticpower sensor (ca. 1981) coupled thelight from the 0.004 inch fiber pig-tail into a fly-speck-sized black ther-mistor bead (about 0.010 inch diam-eter), heated the bead, and meteredit much like microwave power.

Soon came more sophisticated opti-cal power meters, directly suited forhigh-performance characterizationof sources and fibers. The 8151Aoptical pulse power meter (ca. 1985)offered several interfaces to fibersand sources and featured a well-thought-out design with two powerheads covering the 550 to 950 nmand 950 to 1750 nm ranges pre-ferred for optical fiber applications.

At about the same time, HP intro-duced the 8150A optical signal source,which provided a calibrated opticalpower source for the short-wavelengthwindow of 850 nm. Combined withthe 81519A optical receiver and theoptical power meter, these completed

a test-bench layout for parametrictesting of fiber technology.

Several innovations in optical-pathmanipulation produced continuousattenuation control and interfacing tovarious fiber standards of the time. By1987, HP had introduced a new familyof stimulus-and-response equipment.The 8154B LED source, 8152A opticalaverage power meter, an optical atten-uator, and an optical switch addedgreater versatility to the toolsrequired by optical design engineers.

As more fiber was manufacturedand installed, the 8145A opticaltime-domain reflectometer (ca.1988) helped engineers characterizetransmission characteristics of longlines of fiber. Since only limitedpeak-pulse power was achievable atthat time, the OTDR exploited a veryclever, correlation-based, long-pulsetechnique to extract reflected sig-nals from noise and to look fartherdown the length of fiber.

The 8702A lightwave componentanalyzer (ca. 1989) was basically anoptical modulation analyzer forbandwidths up to 6 GHz at 1300 nm,and 3 GHz at 1500 nm. It showed ingreat detail how lightwave transduc-ers (sources and receivers) modifiedthe information-carrying signal. Italso boasted a new technique called

Lightwave communications

For field testing, today’s E6000A mini-OTDR combines powerful measurement tools in a rugged, portable package.

The 8541A OTDR helped engineers characterize lon glines of fiber.


OFDR (optical frequen-cy-domain reflectome-try). By processing thefrequency-responsedata on a computer, thedesigner could deter-mine time- or distance-related imperfections.

The 71400C lightwavesignal analyzer (ca.1988) was the firstpiece of test equipmentthat could characterizethe modulation of optical signals up to 22 GHz. Measurements of RIN and optical distortion were provided in a calibrated system.This innovation was followed in1991 by the 20-GHz 8703A lightwavecomponent analyzer, which was thefirst commercial product incorpo-rating a high-speed, Lithium-NiobateMach-Zehnder modulator, used to create the 20 GHz modulatedoptical signal.

The 8153A lightwave multimeter (ca.1991) used plug-in modules to pre-cisely measure fundamental quanti-ties such as optical power and loss.Available plug-ins included opticalpower meters, fixed-wavelength lasersources, and an optical return lossmodule. The optical power metersbecame industry standards in the 90s.

In 1993 came other families of opti-cal instruments. The 71450A opticalspectrum analyzer and the 8168A

tunable source(one of the firstcommercial tun-able lasers onthe market)offered design-ers powerfulnew ways tocharacterizetheir compo-nents andsources.

The mid-1990ssaw some of themost dramaticand rapid instal-lation ever of anew technology.Development ofthe ingeniousErbium-dopedfiber amplifiermade possiblethe distributed,broadbandamplification of signals.Wavelength mul-tiplexing offered

up to 120 channelcapacity in the samefiber. Huge capacity fordigital communicationswas in sight—none toosoon, since the Internetphenomenon was justgetting underway.

As the world’s trans-mission capacity dou-bled, re-doubled, andthen went up by factorsof 100, the Internet and

the digital communications revolutiongobbled up capacity. No one knowswhen or if the demand for high band-width will end, but most people recog-nize that without test and measure-ment, this communications revolutionwouldn’t have been possible.

Today Agilent’s optical test equip-ment blankets the industry. For optical component testing there aresources, analysis equipment, andautomatic test systems for high vol-ume manufacturing. For field instal-lation and maintenance there areoptical TDRs (OTDRs), optical multi-meters, and wavelength meters.Agilent systems test chromatic dis-persion, polarization, and the uniqueErbium-doped fiber amplifiers. Fiber modulation testers can analyzethe digital intelligence transmitteddown the lines. A family of grating-based spectrum analyzers attacksthe wave-division multiplex technol-ogy that enables the remarkable120+ channels per fiber.

Agilent’s OmniBER family of commu-nications performance analyzers arethe market-leading SONET/SDHtesters, testing telecommunicationstransport networks at optical rates to 2.5 Gb/s. The 71612A 12 Gb/s pat-tern generator and error detector hasbecome the industry standard testerin labs and production lines for testof optoelectronic components andsystems in the new, high-speed opti-cal Internet operating at 10 Gb/s.

The 86140 series optical spectrum analyzers have the high sensitivity, widedynamic range, and exceptional sweep time need to test the current generation ofWDM components and systems.

Portable SONET/SDH test sets measure optical rates to 2.5 Gb/s.

27

There is a broad category of test andmeasurement instrumentation thatserves the R&D engineers designingRF and microwave components, allcrucial for high performance commu-nications systems. These componentsinclude amplifiers, mixers, filters,combiners, antennas, couplers, oscil-lators, attenuators, and terminations.With many real breakthroughs, HPand Agilent have been primary con-tributors of R&D bench instrumentsfor component design and test.

Vector network analyzers are impor-tant tools. As described earlier, the8410A network analyzer of 1968 ush-ered in a revolution in componentdesign and test. Multi-band sweepsof Smith Chart characterizations ofcomponents and systems arrived atjust the right time for exploitinghybrid microcircuit technology forcommunications systems.

HP continued to dominate the vectornetwork analyzer category fordecades, with lower-frequency rangeas well as higher-capability prod-ucts. The 8753A vector analyzer (ca.1987) covered 3 GHz. Sometimescalled the 8510’s little brother, itwas the first low-cost VNA operatingbelow 3 GHz. This positioned it per-fectly for cellular design and testengineers working in the 800 to 900MHz frequency range, and later 2400MHz range. The 8753 was also thefirst RF analyzer to have completeerror-correction.

Along with the flashy vector networkanalyzers, another important (andmore numerous) type of componentdesign tool were scalar network ana-lyzers. Scalar parameters were con-sidered entirely adequate for pro-duction line test assurance, andthese analyzers measured SWR(standing-wave-ratio) and reflectioncoefficient, as well as transmissionparameters.

The first implementation of scalaranalyzers was the reflectometer tech-nique that HP pioneered in 1954.This technique used back-to-backwaveguide directional couplers, amotor-swept klystron 670A signalsource, and a 416A ratio meter totest waveguide components at all fre-quencies across their band. Systemswere developed for waveguide bandsfrom 2.6 to 40 GHz, and for mostcoaxial bands.

Next came the 890-series sweep oscilla-tors, which exploited backward-wave-oscillators (BWOs) for signal genera-tion, making the sweep electronic. Thisled to oscilloscope displays with cali-brations grease-pencilled onto the CRTscreen—not a very aesthetic solution.The 1416A SWR display (ca. 1966)solved that with a scope plug-in thatprovided calibrated reflection andtransmission data.

Other families of sweep oscillatorsfollowed, with the 8690-series andeventually the 8620A-series (ca.1970), which featured solid-state YIGoscillator sources for the first time.HP’s microwave-component researchlabs contributed exceptional resultscoupling microwave transistors withYttrium-iron-garnet technology toyield exceptionally stable and high-power sources.

Later came the 8350 and 8340-seriessignal sources. While early sweepingsources were free-running, sophisti-cated vector network analyzersrequired phase-locked stability forproper error correction. The 8340-series sweeping synthesizers werefar more than just sweepers.

RF and microwave component design

In the late 1960s, the 8410A network analyzer ushered in a new era in component design and test.


HP offered a continuing family ofRF/microwave scalar analyzers,starting with the 8755 frequencyresponse measuring system of 1972.This was a plug-in for the 180 oscil-loscope family, which was specifical-ly designed as a system for scalarparameter testing. The complete sys-tem included dual directional cou-plers for forward and reverse signalseparation, RF/microwave multi-band directional bridges, and a newfamily of wide-dynamic rangeSchottky diode detectors. It used 30kHz microwave modulation toextend stability and range.

The 8756A and 8757A scalar net-work analyzers followed in turn,each with more measuring capabili-ty and higher frequency ranges, withthe 1985 capability at 60 GHz.

HP’s 8970A noise figure meter (ca.1983) pleased circuit designersbecause they could measure and dis-play the gain and noise figure para-meters of amplifiers, mixers, andconverters at the same time. Sincecircuit designers will gladly trade offa little gain to improve the noise fig-ure of an input amplifier, this capa-bility proved highly popular for crit-ical applications such as satellitereceiver front end design. An earlier340A noise figure meter (ca. 1958)measured only noise figure and notgain, so it had only limited useful-ness for component work.

Design engineers of RF andmicrowave oscillators destined forlocal oscillator applications in mostcommunications systems have par-ticularly difficult tasks, becausewhile their VCO (voltage-controlled-oscillator) usually must be agile toachieve channel tuning, it must atthe same time have the lowest phasenoise characteristic to minimize out-of-channel interference.

HP’s first product to characterizemicrowave phase noise was the11729A carrier noise test set (circa.1983). By downconverting the sig-nal under test using an exceptional-ly “spectrally clean” signal, theclose-in noise spectra could be mea-sured and displayed for analysis. In

1985, the 11740A phase noise mea-suring set combined the 3047Aspectrum analyzer and the 11729Bfor a complete solution. The laterE5500A-series phase noise mea-surement solutions covered oscilla-tors to 26.5 GHz.

A complete test solution for voltage-controlled-oscillators (VCOs)became available in 1996 with the4352S VCO/PLL signal test system.This unit characterized 12 differentparameters of the VCOs with clevertechniques to speed the tests, andthey can be installed as productiontest equipment in high volumeassembly applications.

The first simple impedance metersarrived with the acquisition of theBoonton Radio Company in 1960.The 250A (Boonton) RX meter mea-sured reactance to 250 MHz and theunique 260A (Boonton) Q-meter (50MHz) were industry standards ontheir own merits.

At about the same time (1962), HP’s4800A impedance meter (500 kHz)and 4815A impedance meter (500MHz) were introduced. The 4815Aused the brand new HP samplingtechnology, which downconvertedthe two channels and measured anddisplayed impedance and phase andgain characteristics. Each meter wassupplied with a variety of imped-

ance bridges (components that sepa-rated forward and reverse signals)and probing accessories. For designengineers, the insight gained aboutamplifiers and a wealth of circuitcomponents speeded RF work considerably.

Component measurement technolo-gy grew to encompass many otherhighly important functional parame-ters. For example, EMC (electromag-netic compatibility) became a legalrequirement just about the time digi-tal integrated circuits came intotheir own. Signal leakage, whichsome referred to as electronic smog,could interfere with adjacent equip-ment or test instruments in twoways. If a piece of test equipmentwas operating in an environmentwith a high power transmitter, andthe equipment’s susceptibility washigh, it could be jammed by the high-level signal. If its own EMC outputwas not designed to be low, its digi-tal circuits and RF oscillators couldleak enough level to disturb othermeasurements in the area.

RFI (radio frequency interference)measuring receivers of the 1970swere generally mechanically tunedand cumbersome to use. By appro-priately modifying some early spec-trum analyzers, HP was able to inno-vate the measurement technologywith the addition of common anten-

The 8757A scalar network analyzer measured scalar parameters of components to 60 GHz.

nas and probes. The 85650A quasi-peak adapter (ca. 1982) was an earlyexample of an instrument which,when added to spectrum analyzers,gave broad electronic sweep capabil-ity and thereby offered the designera wide bandwidth to search for leak-age signals. It also provided precise,calibrated data.

With the advent of the 8540A auto-matic network analyzer in 1968, HP had a measuring tool whichcould measure the complex ampli-tude and phase characteristics of RFand microwave antennas. In fact,the technology led to the develop-ment of near-field antenna measur-ing ranges. By manipulating thenear-field data of an antenna pat-tern, computer models could predictthe far-field performance withoutdepending on a large outside mea-suring range. For military communi-cations, the ability to use a small,inside closed range offers obviousadvantages.

Other developments focused on the job of totally characterizingantennas. Today the product lineincludes antenna measurement systems as well as a wide variety of accessories such as computer-controlled pedestals.

In the 1970’s, engineering responsi-bility for RF impedance measuringinstruments transferred to HP’s division in Hachiogi, Japan. Soonpowerful, multi-function metersrolled out, featuring many highlyinnovative probing stations andholding fixtures. This was not sur-prising, given the large amount ofindustrial engineering that involvedprinted and integrated circuit tech-nologies being done at this time forconsumer electronics.

Typical instrumentation now offeredsuch capabilities as LCR characteri-zation (with the 4263B LCR meter),crystal resonator measurements(with the E4915A crystal impedancemeter), and dielectric and magnetictest (with the 4291B impedancemeter/material analyzer). Solutionsincluded software routines to pro-vide design engineers with the latestmeasurement routines, so theywould not have to spend timeresearching the field for new mea-surement techniques. For Agilenttoday, selling the measurement tech-niques has become as critical as sell-ing the hardware.

One final type of instrumentationwas the combination spectrum/net-work analyzer. Consider that spec-trum analyzers are single-channelsweeping superheterodyne receiversand vector network analyzers aretwo-channel versions. By cleverlyconfiguring a single-channel circuitso that it could also switch its mea-surement between two networkinputs, and by exploiting micro-processor signal processing, HP gavebirth to the combination 4395A net-work/spectrum/impedance analyzer(ca. 1997). It is especially useful fortesting communications componentssuch as amplifiers and mixers inwhich both network and signal char-acterization is required.

29


Some instrument types are so widelyused that they could logically fit inany communication test sector. Twoobvious examples are the oscillo-scope and the spectrum analyzer.When HP began manufacturingscopes in 1958, the company becameknown for several innovations: qual-ity, low frequency scopes (below1000 MHz) suitable for many produc-tion applications; sampling scopes;and TDRs. HP’s designs also includ-ed many convenience features,including beam finders and internalgraticules on the CRTs that eliminat-ed parallax errors in readout.

On the benches of communicationengineers, spectrum analyzers are asubiquitous as oscilloscopes. Theyanalyze the frequency domain of sig-nals with indispensable diagnosticpower. From the first 8551/851 ana-lyzer of 1964, HP never stopped inno-vating. Many spectrum analyzersbecame the starting point for othermeasuring instruments such as elec-tromagnetic compatibility analyzers,antenna testing systems, and others.

Modern spectrum analyzers, such asthe ESA series, feature digital filter-ing and all the advantages of thedigital age. Still others have fre-quency ranges to 110 GHz, and mea-sure phase noise and even noise fig-ure. Used with tracking generators,some spectrum analyzers can incor-porate measurement of scalar net-work parameters.

The 8590-family portable spectrumanalyzer (ca. 1988) became a fruitfulprogenitor. By downloading a mea-surement “personality” from a card,users could configure the hardwareand firmware of this highly compactsignal analyzer to perform specialapplications. Cable TV, mobile radiotesting of many types, noise figuretests, EMC, and a dozen more appli-cation personalities featured customCRT display calibrations, and theanalyzer had an internal card cage toaccept hardware circuits for uniquesignal handling.

HP and Agilent have dominatedmicrowave power measurementssince the first 430A power meter andassociated 475A bolometer wereintroduced in 1950.

Microwave sensors absorb powerfrom a transmission line and heatup. By detecting the heat-causedchange in resistance of metallic orthermistor elements, the first powermeters could measure and displaypower. The technology was useful,but frustrating for engineers whohad to detect very low power, sincethey found that just holding a sensorin their hands was enough to makethe meter drift off scale.

A major contribution was made in1961, when the 431A power meterwas introduced to take advantage of adual-thermistor design. This designreduced drift 100-fold and also couldmeasure down to 1 microwatt. Awhole line of 478/86A sensors cov-ered a frequency range from 100 kHzto 40 GHz and later to 110 GHz. Olderengineers still fondly remember theintroduction of this useful concept.

The next big step in microwavepower measurement came in 1974,with the introduction of the 435Apower meter and its associated8481A power sensor family. This

sensor family was a clever exploita-tion of a special silicon chip fabrica-tion process that placed a broadbandmicrowave termination on one sideof a thin silicon web, and a sensitivemetallic thermopile on the opposingside. The meter measured theabsorbed heat down to 3 mW and upto 20 mW. Since the sensor was atrue power sensing device, it was“square-law” over its entire range.

The 436A digital power meter (ca.1975) provided important program-mability for the popular HP InterfaceBus and also featured a new 8484Apower sensor, which used thesquare-law detection characteristicof a temperature-isolated diode tomeasure down to an amazing 100pW. The 437A power meter and the438A dual power meter appliedmicroprocessors to provide moreconvenience and functional power tomeasurements.

In 1997 a new family of powermeters and sensors was introduced.The EPM-series power meters tookadvantage of new ultra-wide-dynamic range sensors, the E-seriespower sensors, to measure from -70to +20 dBm in a single sensor. Suchrange permitted measurementsright at the receive antenna ofmicrowave radio systems.

General communications applications

The 8590 series portable spectrum analyzers could be customized for cable TV, mobile radio, noisefigure, EMC, and other applications using software measurement personalities.

31

There are a few measurement con-tributions that do not involve instru-ments, yet cross all lines of commu-nications and are worthy of recogni-tion. This section will list a few.

The step-recover-diode is one ofthese contributions. In the early1960s, engineer Frank Boff wasworking on harmonic-comb genera-tors to extend the frequency rangeof counter frequency converters.One circuit showed non-intuitiveresults, with high frequency har-monics that were more powerfulthan theoretically possible from anon-linear resistive device such as adiode. To investigate further, he bor-rowed an early lab prototype of theHP sampling scope to display a time-domain picture of what was produc-ing such rich signals in the frequen-cy-domain. When he finally got thefuzzy picture focused, he didn't seethe expected chopped-off top of asine wave produced by a diode, but instead saw a sine wave thatrose smoothly to almost full ampli-tude, then suddenly crashed to nearzero amplitude.

At that point, serendipity entered.Frank remembered seeing a paper inthe IEEE proceedings that theorizedthat such a waveform might exist ifa device exhibited a non-linearcharge-versus-voltage curve insteadof the non-linear current-versus-voltage curve that defined a diode.Frank reviewed the article, lookedagain at the strange wave-shape,and proclaimed that what he hadtaken to be a non-linear resistor, ordiode, was actually a non-linearcapacitor under certain conditions.

What he had developed was a varia-tion of the well-known P-N diodethat enhanced the stored carrierphenomenon and achieved anabrupt transition from reverse-stor-age conduction to cutoff. The devicewas able to switch tens of volts orhundreds of milliamperes in lessthan a nanosecond. The result wasthe ability to generate milliwatts ofharmonic power at 10 GHz from sta-

ble oscillators running at 200 MHz.Discovered by an extraordinaryengineer, the device was called the“Boff diode” for a number of years.The name was later changed to themore generic “step-recovery-diode.”

HP exploited this new capability in avariety of ways. HP counters used theharmonic-comb signals to downcon-vert test signals for counter coverageto 18 GHz. The 8410 network analyzerused a two-channel version to down-convert microwave signals for charac-terizing scattering parameters to 18GHz. Sampling oscilloscopes, afterprototypes were used to discover theeffect, in turn used the diode to gen-erate large sampling impulses formeasurement of fast-transition testsignals. A whole generation of HP sig-nal generators and sweepers used therich harmonics to stabilize microwavesignals using the technique of indirectfrequency synthesis.

HP also became the world leader inexploiting phase-lock loops for fre-quency control and programmableswitching of microwave oscillators.Using step-recovery diodes to pro-vide rich harmonics from stable low-frequency oscillators and using syn-thesis techniques such as “divide-by-n,” sophisticated phase-lock loopswere created to disciplinemicrowave oscillators and reducetheir phase noise. In fact, using the312A selective voltmeter and anassociated tracking generator, HPdesigned a new phase-loop measur-ing technique that produced a signalequal to and tracking with the tunedfrequency of the 312A. This combi-nation characterized the closed loopperformance of feedback loops, vali-dating the fast switching responseand loop stability under wide envi-ronmental performance.

The HP Interface Bus (ca. 1972) wasa solution pioneered by HP to pro-vide a practical system for program-ming electronic instruments undercomputer control. By developing thesystem in conjunction with anIEEE/industry committee, this

“open system” created a powerfuldesign capability for applicationsranging from research and design toproduction and support.Instruments from many manufactur-ers designed with the HP-IB func-tionality could be “daisy-chained”together to furnish stimulus test sig-nals, and measurement data couldbe taken from a multitude of volt-meters, analyzers, and other mea-suring instruments. The resultingdata could be conditioned, manipu-lated, and stored.

The IEEE standard became bestknown as the GPIB, or GeneralPurpose Interface Bus. It was accept-ed by test engineers for its powerfulability to configure large or smalltest systems. And as an open stan-dard, it was acceptable to all.

Fast signal sampling technology ofthe late 1960s enabled another pow-erful analysis tool to be invented.Recognition that a single electricalevent, such as a pulse, contains allthe mathematical information need-ed to define its frequency spectrumgave birth to the Fast-Fourier analyz-er. The 5451A Fourier analyzer (ca. 1972) made it possible to

General technology contributions

The HP 35 pocket calculator changed the waywe all do math.


achieve real-time spectrum analysisto 300 Hz. That made possible appli-cations in underwater acoustics,medical instrumentation, and vibra-tion analysis. The technology wasused in later products with evenmore amazing results because offaster and more powerful digitalcomputation. The FFT technique wasexploited in HP's 89410-series vectorspectrum analyzers, described earli-er, and used for highly sophisticatedcommunication modulations.

No listing of the company’s technicalcontributions could be complete with-out mention of the design engineer’spersonal companion, the HP 35 pocketcalculator. Introduced in 1972, this(mostly) electronic engineer’s tool rev-olutionized calculation, replacing sliderules and desktop computers for manyof the engineer's daily computations. Itprovided unparalleled accuracy fortranscendental functions and offeredmany other engineering parameters—all in a package that fit into a shirtpocket. With four computing registers,reverse Polish notation format, aremarkable 200-decade computingrange, and 15 digits, it was an immedi-ate hit even at the $395 selling price.

The 2116A instrumentation comput-er (ca. 1967) brought measurementand control right to the engineer’stest bench. The strategy of the com-puter’s design was to provide anaccessible card cage on the bottomlayer of the product, which allowedprogrammable instruments to beconnected to the computer. Eachinterface card controlled one instru-ment, either a stimulus instrumentsuch as a signal generator or dcpower supply, or a measurementinstrument such as fast a DVM,counter, or spectrum analyzer.

From today’s perspective, theseautomatic systems seem primitiveindeed, having the interface of aclacking teletype with punchedpaper tape. The original 2116A con-troller had a memory based on fer-rite core technology; basic memorysize was 4096 16-bit words (expand-

able to 8K, at $1 dollar per byte.)Storage disks arrived later, as didterminals with CRTs. The real con-tribution of the 2116A was thatunlike business computers of theday, it didn’t need to be coddled.The 2116A was designed specificallyfor the hostile environment of thefactory floor.

The HP 9100A calculator (ca. 1968)was the first desktop computer forHP. Conceived before the availabilityof integrated circuits, its 32-KbitROM consisted of a 16-layer printedcircuit board loaded with thousandsof discrete diodes. It featured a CRTdisplay with 3-display registers andReverse Polish Notation, and it revo-lutionized the expectations of designengineers. It led directly to the 1972family of 9810/20/30A programma-ble calculators (which would now becalled desktop computers), whichhad HP-IB automation capability.

In addition to integrating instru-ments with the HP-IB, in 1987 HPled a consortium of major instru-ment manufacturers to devise amodular architecture, the VXI. Thisarchitecture relied on the previouspopularity of the computer-indus-try-standard VME technology, and itinitially focused on low frequencyand RF. Conceived for portableapplications, including military,custom measuring applicationswere configured into standardizedmodular cages. Dozens of availablecompatible instrument solutions

from multiple suppliers are nowavailable, and software routines canbe devised to control the measure-ment process, many now using themodern plug-&-play concepts ofhardware and software.

A similar open standard was intro-duced for microwave applications,the modular measurement system(MMS). It was built for higher-fre-quency signal performance withmuch more attention given to elec-tromagnetic compatibility andRF/microwave signal routing.

The modular architecture of VXI enabled development of “instruments on a card.”

33

Over the decades Agilent has intro-duced many groundbreaking prod-ucts. Picking the superstars of com-munications test is personal, buthere are some of our favorites.

The 5060A cesium beam standardcould arguably be credited with stan-dardizing the technology clocks ofthe world. HP engineers undertookthe first “Flying Clock” project in1964, flying two atomic clocks toEurope to precisely compare the U.S.Naval Observatory time with officialclocks in Switzerland. Atomic fre-quency standards had been devel-oped in many countries to serve asthe basic reference based on theatomic resonance principle, unvary-ing and fundamental. The 5060A,designed for rugged performance andlong term reliability, became the firstcommercial product-of-choice inindustrial primary-standards labs. Itand a long line of progeny came todominate the time and frequencystandards labs of the world. Sincetoday’s communication technologyrelies heavily on synchronized trans-mission frequencies, everything fromcellular base stations and broadcasttelevision stations to satellite flyingoscillators must incorporate suchprecise and stable standards.

The 185A/187A sampling oscillo-scope (ca. 1960) was a giant leapahead in RF and digital measure-

ments. Using sampling technology,this scope permitted engineers tomeasure exceedingly fast transitiontimes for repetitive, pulsed wave-forms. It featured a sophisticatedtriggering circuitry for viewing actu-al RF waveforms to 1000 MHz. Thesame sampling scope technology leddirectly to the 1415A time domainreflectometer plug-in. The ability toview the time separation of reflec-tions from a coaxial transmissionstructure enabled engineers to diag-nose reflections from individual ele-ments. For example, the individualattenuation elements of the 355AVHF attenuator could be seen andeach tweaked for exact 50-ohm per-formance, whereas if all werelumped together in an SWR mea-surement, no corrective adjustmentscould be made. This translated intogreat design power for circuit engi-

neers working on components forcommunication projects, whichrelied heavily on coaxial and strip-line transmission structures.

Although microwave spectrum ana-lyzers had served the communica-tions industry since the days ofWWII, they were cumbersome to useand had narrow dispersions and onlymodest dynamic range. In 1964, HPintroduced its first spectrum analyz-er and revolutionized the conceptand functionality of the instrument.The 8551A/851A spectrum analyzer,with its 2000 MHz sweep width andits 10 MHz to 12 GHz (or 40 GHz withexternal mixers) tuning coverage wasa marvel of the time. It featured aswept first local oscillator, which wasa backward-wave-oscillator, toachieve a wide sweep width. For highstability in narrow sweeps, it used anew technique for phase-locking to asweeping VHF source.

For the first time, engineers couldlook at a huge baseband range andcharacterize the performance of com-ponent and system signals for ampli-tude and harmonic performance. Forexample, an amplifier could beshown with the fundamental signalsand all the signal harmonics. Theinstrument featured an amplitudedynamic range of 60 dB, and therebybecame accepted as a “frequency-domain-oscilloscope.” Spectrum ana-lyzers soon became as ubiquitous onmicrowave design benches as time-domain scopes were on the benchesof low-frequency engineers.

An evolution of spectrum analysisinstruments ensued. Smaller size,absolute amplitude calibration, andinnovative features such as trackinggenerators made frequency-responsemeasurements simpler. Solid-statelocal oscillators made the productsmore stable and reliable. Plug-indesigns allowed selection of differ-ent frequency bands and conversioncircuits. Eventually spectrum ana-lyzers were integrated into automat-ic systems using modular construc-tion that mimicked the versatileplug-in design of laboratory scopes.

Superstars

The 185A oscilloscope was a giant leap aheadin RF and digital measurement.

The 5060A cesium beam standard was used to set the world's clocks.


In 1978, a new generation of spec-trum analyzers took full advantageof microprocessors. In fact, theseanalyzers used three processorseach. The HP 8568A and 8566A spec-trum analyzers—affectionatelyknown around HP as the “dooms-day” machines—had better frequen-cy-tuning accuracy, narrower resolu-tion, lower phase noise, and betterphase-lock stability. But the biggestfeature was the human interface.These were among the first instru-ments with a lower panel that lookedlike a calculator keyboard. A singlerotary knob gave selectable analogfeel for tuning, but the keyboardoffered digital precision. Powerfulmarker functions allowed markingand measuring of differencesbetween traces. And powerful com-putation routines stored traces sothat one trace could be subtractedfrom another. Maximum signalscould be monitored and stored. Mostengineers operating this machine forthe first time were dazzled by theperformance. The spectrum analyzerhad now truly become the “frequen-cy domain oscilloscope.” And withthe HP-Interface Bus (which becamethe IEEE-388 or GPIB), it formed acentral measurement instrument foreven more powerful, automatic spec-trum monitoring systems.

Following 1968’s two-channel 8405Avector voltmeter, the 8410A vectornetwork analyzer (VNA) of 1968 rev-olutionized the characterization ofmicrowave components from 10 MHzto 12 (soon 18) GHz. With itsmicrowave sweeping source and theassociated signal-separation test set,the network analyzer met its originalobjective: to “stamp out slottedlines.” Before this, engineers had touse tedious slotted-line measure-ments to compute a Smith-Chartplot, frequency by frequency.

The VNA’s intro-duction came at apropitious time,since themicrowave semi-conductor revolu-tion was just gain-ing headway indesign labs aroundthe world.Microwave micro-circuit technologyshrunk the size ofamplifiers andintregrated circuit-ry, and demandedtotal knowledge ofthe compleximpedance of allthe semiconductorchips and on-sub-strate componentssuch as filters, cou-plers, and mixers.

The availability of the VNA popular-ized the design concept of scatteringparameters, which are characteriza-tion data in complex impedance for-mat, for two-port and N-portmicrowave components. Providedwith actual Smith-Chart oscilloscopedisplays or phase-gain plots versusfrequency, communications design-ers gained powerful insights intotheir circuitry. In the microwavesemiconductor revolution of the1970s, designers raced to developthin-film-on-sapphire integrated-cir-cuit technology to combine thepower of microwave transistors witha variety of circuit elements, includ-ing directional couplers, filters, mix-ers, converters, terminations, andlumped-circuit components such asinductors and capacitors. The broad-band network analyzer becameindispensable for that role.

The 8510A network analyzer of 1985brought full circle the tremendousinsight that component design engi-neers first realized with the 8410A.Combining the new power of themicroprocessor with the earlier ana-lyzer’s extensive capability for char-acterizing components and systems,the 8510A launched a revolution. Full of user operating features anderror-correction routines, this 26.5GHz component analyzer pushed intonew application areas. For example,it was able to process frequency-domain data and render a time-domain characteristic of the signalpassing through a complex sub-sys-tem on a chip.

The power of the 8510A resulted innumerous, unexpected applications.With special probing antennas andinnovative software routines, dielec-tric characteristics of microwavematerials could be measured. Micro-miniature probing stations andfixturing were developed for wafertesting. Special detection equipmentand routines could measure pulsedcomponents that could not surviveCW signals.

Importantly, the powerful measuringcapability provided by the 8510T net-work analyzer system (ca. 1987) wascombined with RF and microwave

The 851A spectrum analyzer, with its wide sweepand tuning range, was a marvel of the early 1960s.

The 8510A network analyzer combined the power of microprocessors withextensive measurement capability to launch a revolution in component test.

35

circuit-design modelingsoftware. This processprovided the verificationfeedback needed to con-firm that circuits and fab-rications worked accord-ing to the design model.HP’s EEsof Division andother companies such asCompact invented sophis-ticated microwave circuit-design models in theirAdvanced Design Systemsoftware. Now the entirecommunications signalpath could be simulated,from the data stagethrough microwave cir-cuits and antennas backto the data stage.

The acceSS7 signalingmonitoring system took onthe world’s networks, literally, whenit was introduced in 1996. Designedto provide network operational mon-itoring on a vast scale, it specificallytargeted the world-standard CCITTSS7 common channel signaling pro-tocol. The design grew out of the ear-lier 37900A/C/D signaling test sets.

Scalable and non-intrusive, theacceSS7 measures and displays real-time information on SS7 switchingdata activity, and provides the plat-form for a host of network monitoringand management and business intelli-gence applications. For example, itprovides security and fraud operatorswith automatic real-time messagingstatus for detecting and reporting sus-picious telephone activity. TheacceSS7 databases gather key market-ing information, such as usage vs.capacity, call duration, and unan-swered calls. Such data can be used byservice providers to optimize benefitsand services. By keeping a constantwatch over revenue-critical opera-tions, the acceSS7 system can generateinformation vital to management deci-sions on network operations, bothhardware and software. The globalmeasurement reach it provides givessystem operators advance noticebefore network performance deterio-rates, even by small increments.

Other candidates for the communi-cations superstar category are many:

• The 3710A microwave link analyz-er family, introduced in 1967,became the industry standard forinstalling microwave radio links inNorth America and Europe.

• The 3760/61 pattern and errordetector of 1973 was the world’sfirst commercial 150 Mb/s error ratetester. It helped engineers developthe first generation of digital trans-mission systems. Through severalgenerations it has led to Agilent’sOmniBER family of testers, the mar-ket-leading SONET/SDH testersworking to 2.5 Gb/s. In 1994, the71612A 12 Gb/s pattern generatorand error detector was introduced,and it has become the industry stan-dard tester in labs and productionlines for test of optoelectronic com-ponents and systems in the new,high-speed optical internet operat-ing at 10 Gb/s.

• Launched in 1975, the 3745Aselective level measuring set wasHP’s first microprocessor-controlledinstrument that accelerated the test-ing and troubleshooting of frequencydivision multiplex (FDM) telephonesystems by automatically tuning thereceiver to the FDM frequency plan.

• A family of compact,portable cellular testsets, launched in 1992,combined measurementsof many instruments fortransceiver testing ofland-mobile and cellularapplications. Variationswere developed to meetnew system formats suchas North AmericanDigital Cellular (NADC),GSM, TDMA, CDMA; forDECT (Digital EuropeanCordlessTelecommunications);and even for pagers.Today Agilent’s test setsfor mobile phone manu-facturing dominate theindustry.

• In the early 1990s, HPextended its range of test for ATM(asynchronous transfer mode) andbroadband applications by introduc-ing the Broadband Series TestSystem. The BSTS has been on theleading edge of ATM technology forswitches, routers, and network ser-vices, and it continues to support agrowing number of protocols thatcarry voice, data and video services.These include ATM, frame relay,LAN, LAN internetworking, MPEG-2,UNI signaling, NNI signaling, W-CDMA, and more.

The legacy of innovation continuesas Agilent provides the communica-tions industry with innovative testand measurement products such asoptical spectrum analyzers, a voice-controlled oscilloscope, voice overIP testers, the industry’s first gigabitand terabit router testers, 3G wire-less solutions, and many more prod-ucts. On the frontier of new technol-ogy, Agilent has launched a family ofoptical switches that may lead to therealization of the much-anticipatedall-optical communications network.

The acceSS7 signaling network monitoring system provides network opera-tional monitoring on a vast scale.

By Internet, phone, or fax, get assistancewith all your test and measurement needs.

Online assistance:www.agilent.com/find/assist

Phone or fax

United States:Agilent Technologies(tel) 1 800 452-4844

Canada:Agilent Technologies Canada Inc.(tel) 1 877 894-4414

Europe:Agilent TechnologiesTest & MeasurementEuropean Marketing Organization(tel) (31 20) 547 2000

Japan:Agilent Technologies Japan Ltd.(tel) (81) 426 56 7832(fax) (81) 426 56 7840

Latin America:Agilent TechnologiesLatin American Region Headquarters, U.S.A.

Australia/New ZealandAgilent Technologies Australia Pty Ltd(tel) 1 800 629 485 (Australia)(fax) (61 3) 9272 0749(tel) 0 800 738 378 (New Zealand)(fax) (64 4) 802 6881

Asia Pacific:Agilent Technologies, Hong Kong(tel) (852) 3197 7777(fax) (852) 2506 9284

Product specifications and descriptions in this

document subject to change without notice.

Copyright © 2000 Agilent Technologies

5980-2090E

For more than 60 years, AgilentTechnologies has contributed to thesuccess of communications compa-nies, and our innovations continueto influence the industry in manyareas. Today communications com-panies face waves of new techno-logy, new business models, andincreasing customer demand. Only

those who can take advantage of the change will thrive. AgilentTechnologies plays a continuing rolein the success of these companies,providing the people, technology,components, and tools they need to design, deliver, and manage the next generation of communicationsnetworks and services.

Agilent’s products today

Agilent's wide range of communications offerings today includes breakthrough technology for optical switching, handheld instruments for field-service testing, and drive test systems for optimizing wireless networks.

To read about the latest contributions, please visit us on the Web at www.agilent.com.

Documents

5980-2090E