PROCEEDINGS OF THE IRE

Section 5

BROADCAST AND TELEVISION RECEIVERSOrganized with the assistance of the IRE Professional Group on Broadcast and Television Receivers

The Development of the Art of Receiving from the Early 1920's to the Present by William 0. Swinyard

A Half Century of Television Reception by F. J. Bingley

Development of the Receiving Tube Art and Its Impact on the Receiver Art by E. W. Herold

The Development of the Art of Radio Receivingfrom the Early 1920's to the Present*

WILLIAM 0. SWINYARDt, FELLOW, IRE

Summary-A brief r6sume of important scientific discoveriesleading to radio broadcasting is given. There follows a discussion ofthe most important types of home broadcast radio-receiving circuitswhich came into use after the advent of entertainment broadcasting.These circuits include crystal receivers, regenerative receivers,neutrodynes and superheterodynes. Attention is also given to thedevelopment of automatic volume control, automobile radios andFM receivers.

An effort has been made to present the developments chrono-logically with attention primarily being given to the work of leadingpioneers.

In the final part of the paper some of the more important innova-tions in the radio-receiving art are mentioned and, in some cases,briefly discussed.

INTRODUCTIONT HE radio-receiving art owes a great debt to early

pioneers-Ampere, Henry, Faraday, and, morespecifically, Maxwell and Hertz. Credit is due

Maxwell for mathematical studies which led to his elec-tromagnetic theory of light and his prediction of theexistence of electromagnetic waves of relatively low fre-quency, and Hertz for being the first to produce them-in 1887, some 25 years later.The first crystal detector was designed in 1906 by

Pickard. It consisted of a silicoin crystal and a catwhisker. At about the same time Dunwoody developeda detector using a carborundum crystal clamped be-tween two brass holders. In 1883 Edison, in seeking thecause of blackening of lamps, discovered current flow in-

* Received by the IRE, October 20, 1961.t Hazeltine Research, Inc., Chicago, Ill.

side a vacuum tube. This led to the invention of thevacuum diode, the "valve," by Fleming in 1904 and tothe invention of the triode vacuum tube, the "audion,"by de Forest in 1907.

However, the triode remained a rather unsatisfactorydevice until 1912 when H. D. Arnold recognized that itsimperfections stemmed largely from its defectivevacuum and the use of a tantalum, instead of an oxide-coated filament. He improved the vacuum and Wehneltinvented the oxide-coated filamnent. With the removalof these shortcomings the triode became the corner-stone of modern radio communications.At the conclusion of World War I many former radio

amateurs, "hams," returned to civilian life with a keeininterest in radio. This interest was greatly sharpened bythe awareness of these men of the radio developments ofthe day. They, along with an ever-increasing number ofother hams, became an enthusiastic group of potentialradio listeners.

In 1920 F. Conrad of Westinghouse converted hisamateur wireless station, which he built in 1916, toradiotelephony and returned to the air. He announcedregular two-hour broadcasts on Wednesday and Satur-day nights and the response in the Pittsburgh area wasvery enthusiastic. A local department store bought asupply of crystal sets which were quickly sold to the"amateur" public. This response paved the way for a de-cision to put the station on a regular broadcasting basis,and on November 2, 1920, Westinghouse station KDKAin East Pittsburgh, Pa., was officially opened and the

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era of radio broadcasting began. The station's initialbroadcast of the Harding-Cox election returns was sen-sational.'

Since that time radio broadcasting has shown a spec-tacular growth. Many of the companies which had beenmanufacturing military equipment started to produce"amateur" sets. Newspapers, department stores andeducational institutions opened their own broadcastingstations. By 1922 there were 30 licensed broadcastingstations in the United States, and by 1924 there wereover 500.

CRYSTAL RECEIVERSBefore and during World War I crystal sets were in

wide usage by radio hams. It was only natural, there-fore, that this type of receiver should be the first em-ployed after the beginning of radio broadcasting. Tuningin crystal receivers was effected by varying either thetuning capacitance or the inductance.The most commonly used crystals were silicon, car-

borundum (silicon carbide) and galena (lead sulphide).The receiver was operated by tuning the circuit to thestation and then assuming the use of a silicon detector,probing the crystal surface with the cat whisker to find asensitive spot, retuning, reprobing, etc. The cat whiskerwas a sharp, firm metal wire and in the case of thewidely-used silicon detector was sometimes made ofantimony. With a good straight-wire outdoor antenna,the range of a crystal set for satisfactory response froma broadcasting station was limited to a radius of 5 to 50miles. All crystal sets suffered from a lack of sensitivityand crystal instability. However, they were availableand were relatively inexpensive and easy to produce.

REGENERATIVE RECEIVERS

Crystal sets were soon replaced by regenerative re-ceivers.2'3 The regenerative circuit (Fig. 1) was inventedin 1912 by de Forest, Armstrong and Langmuir in theUnited States, and by Meissner in Germany. After 20years of litigation, the United States Supreme Courtfinally decided in de Forest's favor. Meanwhile, in 1917Armstrong received the first IRE Medal of Honor forhis work on regeneration and the production of oscilla-tions. After the Supreme Court decision, Armstrong re-turned the Medal of Honor to IRE, but the Board ofDirectors unanimously declined to accept it and re-affirmed the original award.

In the regenerative detector circuit RF energy is fedback from the anode circuit to the grid circuit to givepositive feedback at the carrier frequency, thereby in-creasing the sensitivity of the circuit.

Regenerative receivers marked a big step forward in

' W. R. MacLaurin, "Invention and Innovation in the RadioIndustry," The MacMillan Company, New York, N. Y., p. 112;1949.

2 E. H. Armstrong, "Some recent developments of regenerativecircuits," PROC. IRE, vol. 10, pp. 244-260; August, 1922.

3 E. H. Armstrong, "The regenerative circuit," Proc. Radio Clubof America, April, 1915.

providing greatly increased sensitivity. Inherently theyprovided large amplification of small signals and smallamplification of large signals. By 1922 they had reachedthe high point in their development and had almost en-tirely superseded crystal sets.Three sets captured a large share of the market: 1)

Westinghouse (RC) Radiola, 2) Clapp-Easthan, and3) Grebe. Each of these receivers included a detectorand two stages of audio amplification. In some cases theaudio amplifier was sold separately. At that time onlytwo frequencies were allocated to broadcasting: 300 and360 meters. However, everyone wanted to receive shipsignals on 600 meters (500 kc), and hams on the "short-wave" band, 200-250 meters (1200 to 1500 kc) and thisdemand determined the frequency coverage providedby these early sets.

Fig. 1-Armstrong regenerative receiver.

Regenerative receivers, however, were subject toserious difficulties since they could easily be made tooscillate if the regeneration control were turned up toofar. When the receiver was in an oscillating condition itproduced heterodyne whistles in nearby receivers whenit was tuned to, or through, stations to which they weretuned. This device soon became a public nuisance andthreatened the development of the radio art. Regenera-tive receivers were also hard to adjust, and it was almostan impossibility to operate them so that they would al-ways receive the same station at the same point on thedial. Logging stations was, therefore, impracticable.

NEUTRODYNE RECEIVERSThe neutrodyne circuit was invented in 1918 by

Hazeltine.46 Basically this was a tuned radio-frequency(TRF) amplifier which employed a specific type ofneutralization. A current obtained from the plate cir-cuit was fed back into the grid circuit in the propermagnitude and phase to balance out, or neutralize, theeffect of grid-to-plate capacitance inside the tube, andthus it achieved stability and prevented oscillation. Thegrid-to-plate capacitance of the tubes used in the early

4 F. E. Terman, "Radio Engineers Handbook," McGraw-HillBook Co., Inc., New York, N. Y., pp. 468-469; 1943.

5 MacLaurin, op. cit., pp. 127-129.6 Louis A. Hazeltine, "Tuned radio frequency amplification with

neutralization of capacity coupling," Proc. Radio Club of America,vol. 2; March, 1923.

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sets was high, and in the case of the type 201A was be-tween 8 and 12 pf. Hazeltine originally proposed thiscircuit to stop squealing in audio amplifiers, stating thatit was no doubt also applicable to radio-frequency cir-cuits. In 1922 Hazeltine designed a radio receiver onpaper incorporating his neutralizing circuit. This re-ceiver was a reflex neutrodyne employing three tubesand three tuned circuits, each tuned by a separate tun-ing dial. Magnetic coupling between the unshieldedtuned RF transformers was eliminated by mountingthem in line with their axes inclined 54.7° with respect tothe line of centers. The circuit diagram is shown in Fig.2. A modified version in which a separate audio amplifierwas used was placed on the market by Freed-Eisemannin 1923. This was a five-tube set and was the first sethaving high RF amplification and high RF selectivity.By 1924 neutrodyne receivers were selling by the hun-dreds of thousands.

Fig. 2--Hazeltine reflex neutrodyne receiver.

Hazeltine developed the neutrodyne circuit to a com-

plete solution from a mathematical point of view. Forthis work, along with his conception of vacuum-tubeparameters, specifically mutual conductance,7 he was

awarded the Armstrong Medal by the Radio Club ofAmerica in 1937.

Neutrodyne receivers had stable characteristics;tuning dials could be logged when stations were tuned inand they were easy to operate.

In 1926 a neutrodyne receiver was designed whichemployed shielding between the coils, the shieldedneutrodyne.5 This receiver marked the first attempt atunicontrol. It had two dials (in addition to the volumecontrol); one tuned the antenna circuit and the othertuned three stages of RF amplification. It was offered byStromberg-Carlson and others.

For a number of years any set carrying the name

neutrodyne was certain to sell. However, with the de-velopment of the screen-grid tube in 1928 with its low

7 L. A. Hazeltine, "Oscillating audion circuits," PROC. IRE, vol.6, pp. 63-98; April, 1918.

8 J. F. Dreyer, Jr., and R. H. Manson, "The shielded neutrodynereceiver, ' PROC. IRE, vol. 14, pp. 217--247; April, 1926. "Discussion,"L. A. Hazeltine, pp. 395-412; JunIle, 1926.

grid-to-plate capacitance, the necessity for neutraliza-tionl disappeared and the demand for this reeciver de-clined rapidly.Many sets, neutrodynes and other types, having

tuning capacitors ganged together so that they could betuned by means of a single dial, were manufactured andsold in the late twenties. However, all fell short of trueunicontrol operation since the volume control, or RFgain control, or both, had to be continuously read-justed as the set was tuned over the band in order toavoid inadequate volume or overload (blasting).

AUTOMATIC VOLUME CONTROLIn 1925 the stage was set for the invention of a prac-

tical automatic volume-control circuit, and on January2, 1926, Wheeler invented his diode AVC and lineardiode-detector circuit.91 0 This circuit was first in-corporated in the Philco Model 95 receiver which he de-signed at the Hazeltine laboratory and which wasannounced about September, 1929.11

This receiver employed 9 tubes, two type-224 tunedRF amplifiers, one type-224 untuned RF amplifier, atype-227 connected as a diode detector, a type-227 re-sistance-coupled first AF stage, a type-227 transformer-coupled AF driver, and a push-pull audio output stageusing type-245 tubes. The rectifier was a type 80.Two coupled tuned circuits were employed preceding

the first tube to prevent cross-talk from nearby localstations. The antenna circuit employed a high-in-ductance primary and was designed to provide tuningwhich was independent of antenna size, and uniform gainand selectivity over the band.A type-227 tube with its grid and plate tied together

served as a two-element (diode) detector which suppliedboth an AF signal to the audio amplifier and a dc biasvoltage to the RF amplifiers. Since a two-element de-tector is linear over practically its entire rectificatioiicurve when a high dc impedance is used in its return cir-cuit, as was the case here, it provided the greatly de-sired linear detection characteristic. In this receiver theuseful range of linearity of the detector was from 1 to 10volts, approximately.

Full AVC bias voltage was applied to the first two RFtubes, and, to prevent distortion in the third RF stage,half AVC bias voltage was applied to that stage. Theautomatic volume-control action was sufficientlygradual to permit accurate tuning by ear, and it was un-necessary to touch the volume control once it was ad-justed. With all four tuning capacitors ganiged to acommon tuning dial, true single-knob operation wasprovided for the first time in any receiver. The sensitiv-ity of the receiver was about 5 ,v/m across the band,

HH. A. Wheeler, "Automatic volume control for radio receivingsets," PROC. IRE, vol. 16, pp. 30-39; January, 1928.

10 H. A. Wheeler, 4Design formulas for diode detectors," PROC.IRE, vol. 26, pp. 745-780; June, 1938.

11 XW. E. Holland and W. A. MacDonald, "The Philco '95' screen-grid plus," Radio Broadcast, vol. 16, pp. 111-112; December, 1929.

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and the signal input ratio over which the automaticvolume control was effective was 300 to 1. With a local-distance switch this was increased to 10,000 to 1.By 1932 practically every receiver on the market

used a diode AVC circuit employing a single-diode de-tector to supply both the audio signal and the AVCvoltage. This situation remains unchanged today, in-sofar as electron-tube receivers are concerned.

THE SUPERHETERODYNE

A number of engineers worked on the problem of theproduction of superaudible frequencies by means ofheterodyning. Pioneers in this work were Levy inFrance, Round in England, and Armstrong in America."2The direct outcome of Armstrong's work was the de-velopment of the superheterodyne receiver.'3

In the superheterodyne receiver the signal frequencyis mixed with the locally-generated oscillator frequencyin a nonlinear device to produce two new frequenciescorresponding, respectively, to the sum of, and thedifference between, the two frequencies. The differencefrequency is fed to the IF amplifier where it is amplifiedand then rectified in the detector where the audio-fre-quency component is taken off and fed to the audioamplifier. In early receivers of this type the tube inwhich the signal and oscillator frequencies were com-bined was called the first detector, and the tube whichseparated the audio signal from the modulated IF signalwas called the second detector. Later these terms werechanged to converter, or mixer, and detector, respectively.More precisely, the term converter applies to the com-bined oscillator and mixer functions, which may be per-formed in the same tube.The superheterodyne obtains only a relatively small

part of its gain and selectivity in the antenna and RFamplifier circuits; by far the larger part is obtained at alower frequency in the IF amplifier where gain is moremanageable. Since tuning of the IF amplifier is fixed, amore desirable band-pass selectivity characteristic canreadily be achieved. These factors combine to make itrelatively easy to secure uniform gain, selectivity andfidelity over the band.The first publicly sold superheterodyne receivers were

made by the General Electric Company and placed onthe market in March, 1924, by RCA.14 These receiverswere known as the Radiola Superheterodyne SecondHarmonic, a table model, and the Radiola Super VIII, aconsole model. The table model employed a fixed built-in loop antenna, but did not include a loudspeaker.Batteries were located in side compartments of thecabinet. The console model included a built-in rotatable

12 D. McNicol, "Radio's Conquest of Space," Murray Hill Books,Inc., New York, N. Y., p. 272; 1946.

13 E. H. Armstrong, "The superheterodyne-its origin, develop-ment, and some recent improvements," PROC. IRE, vol. 12, pp.549-552; October, 1924.

14 Prior to 1929, RCA was not a manufacturer. It was a patentlicensing and sales organization owned by General Electric, Westing-house and AT&T. See McLaurin, op. cit., p. 147.

loop antenna and a horn loudspeaker. Both models em-ployed the same chassis which utilized a circuit devel-oped by H. Houck. This circuit employed six UV-199tubes and included an untuned RF stage, second-har-monic converter stage, two IF stages, one of which wasreflexed with the RF stage, an audio detector and twoAF stages. Second-harmonic operation of the oscillatorwas employed to prevent tuning interaction betweensignal frequency and oscillator circuits. The circuitdiagram is shown in Fig. 3.

Fig. 3-Basic superheterodyne second harmonic circuit.

The chassis featured a component assembly called thecatacomb which included the IF, RF and AF componentsand was potted in wax. The RF and IF transformersemployed 3-mil silicon steel laminations, and two of theIF transformers had both primary and secondary tunedto 42 kc and were critically coupled to provide a band-pass selectivity characteristic. Regeneration was re-duced by capacitive neutralization and by magneticneutralization through the common silicon steel core.

Later superheterodynes were designed to operate onthe fundamental of the oscillator, and the IF was raisedto about 175 kc. By 1930 they began to take over, andby 1932 they were in universal use, as they are today.In 1938 the IF was set at 455 kc by the RMA StandardsCommittee.

AUTOMOBILE RADIOS

Transitone began to produce automobile radios inabout 1927 on a custom-made or low-production basis.In 1931 this company was bought by Philco, and theproduct was designated Philco-Transitone. However,Motorola claims to have turned out the first mass-pro-duced commercial auto radio in 1929. This set employeda tuned RF circuit consisting of three gang-tuned stages,an antenna and two RF stages employing type-224tubes, a type-224 detector, a type-201A audio driver,and push-pull type-112A's in the output stage. The 6-volt car battery supplied the filament current and "B"voltage was supplied by three 45-volt batteries. The re-ceiver included a dynamic loudspeaker with a 6-voltfield coil. Signal pickup was effected by means of a

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screen-type antenna mounted in the roof of the car. Thethree-section gang capacitor and the volume controlwere remotely operated by means of flexible shafts run-ning from the metal box housing the receiver to a controlbox mounted on the steering column.The superheterodyne circuit was first used in an auto

set in 1931. This set also employed batteries to supplyfilament, plate and screen potentials. The intermediatefrequency was 175 kc. It was replaced the same year bya set which utilized a wired-in vibrator power pack.

In 1932 Motorola marketed what is claimed to be thefirst auto set which employed a power supply with aplug-in vibrator to furnish plate and screen voltages.This receiver utilized a superheterodyne circuit and em-ployed 8 tubes. The intermediate frequency was 175 kc.It incorporated circuits to filter the battery and plate-supply voltages to reduce ignition noise and vibratorhash.

After World War II, ganged capacitors were scarce,and permeability tuning came into wide usage in homereceivers and in auto sets. Because of the improvementin SNR and freedom from microphonism provided bythis type of tuning-in auto sets, the industry stayedwith "perm" tuning in receivers of this type. The im-provement in SNR came about because the "perm-tuned" antenna circuit could be more efficiently coupledto a low-capacitalnce automobile antenna, thus provid-ing higher antenna gain.The transistor, first publicly announced in 1948, is

said to have been first applied in entertainment-typeautomobile receivers in a set made by Motorola andmarketed in about 1956. In the audio-output stage thisset incorporated a power transistor mounted on a heatsink outside the metal cabinet. All other functions re-quiring electron devices utilized tubes designed tooperate with 12-volt plate, screeni and filament poten-tials which were supplied directly by the car battery.Sets of this type are called hybrid sets because of the useof both tubes and transistors.The main reason for the existence of the hybrid set is

based on economic considerations, transistors being toohigh priced to make completely transistorized auto setscompetitive for the commercial market. Additionally, atransistor was used in the power output stage because itdelivered greater power output than could be securedwith a 12-volt audio-output tube.Some manufacturers made hybrid auto sets which em-

ployed conventional tubes whose plate and screen volt-ages were supplied by a transistorized power oscillator.15

Hybrid auto sets have been very popular from 1956to the presenit. However, they are gradually giving wayto all-transistor receivers as the price of transistorscomes down. It is estimated that by 1963 almost allautomobile sets will be fully transistorized.

15 C. C. Hsu, "Development of the 12 volt plate-voltage hybridautomobile radio receivers-AM, signal seeker and FM," IRETRANS. ON BROADCAST AND TELEVISION RECEIVERS, vol. BTR-4, pp.1-31; March, 1958.

The first all-transistor auto set is said to have beenplaced on the market by Philco in about 1956. It em-ployed a conventional superheterodyne circuit and 12transistors. The intermediate frequency was 262.5 kc,the power output 3.5 watts and the nominal battery cur-rent drain 0.4 ampere at 13.8 volts.

In connection with hybrid and fully-transistorizedauto sets, it should be pointed out that the usual prob-lems of vibrator hum and "hash" no longer exist.

Most early auto sets used antennias which weremounted in the car roof or under the car or runningboard. After "touring" cars were replaced by sedanshaving metal tops, present day whip-type antennascame into general use.

FREQUENCY-MODULATION RECEIVERSThe credit for promoting FM as a broadcast service

goes to E. H. Armstrong. For years he had been seekinga way to reduce static, and finally he turned his atten-tion to FM. Toward the end of 1933 he had perfected asystem of wide-band frequency modulation whichseemed to overcome natural and many forms of man-made static."6 In this system the carrier was frequencymodulated + 75 kc by audio componients up to 15 kc.

In 1938 General Electric placed the first FM receiveron the market their Model GM 125, a superheterodyneemploying 11 tubes plus a rectifier.'7 It was tunable overa range of 41-44 Mc; the IF was about 3 Mc, and thebandwidth was sufficient to handle a frequency devia-tion of ± 100 kc. It employed a type-6SJ7, as a grid-cur-rent limiter to remove amplitude modulation, followedby a type-6H6 double diode in a Foster-Seeley dis-criminator circuit to provide FM detection. It is inter-esting to note that this discriminator circuit wasoriginally proposed in 1936 for use as an automatic-frequency-control detector and came into rather wideusage in this application.'8

In 1945 the ratio detector invented by Seeley cameinto use as an FM detector and was widely adopted,particularly in medium- and low-priced FM receivers,because it did not need to be preceded by a limiterstage."'On January 1, 1941, the FM band of 42-50 Mc came

into general use in accordance with the FCC decision ofMay, 1940, and in August, 1945, the FCC allocated thepresent band-88-108 Mc. In 1946 the Radio Manu-facturers Association (now Electronic Industries Asso-ciation, EIA) proposed 10.7 Mc as the standard FMintermediate frequency and proposed an antenna-to-settransmission-line impedance of 300 ohms.

If S. W. Seeley, "Frequency modulation," RCA Rev., vol. 5, pp.468-480; April, 1941.

17 G. W. Fyler and J. A. Worcester, "Frequency modulation inradio broadcasting-a new Armstrong frequency-modulated wavereceiver," Proc. Radio Club of America, vol. 16; July, 1939.

18 D. E. Foster and S. W. Seelev, 'Automatic tuning, simplifiedcircuits, and design practices," PROC. IRE, vol. 25, pp. 289-313;March, 1937.

"9 S. W. Seeley and J. Avins, "The ratio detector," RCA Rev.,vol. 8, pp. 201-236; June, 1947.

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INNOVATIONS

There have been many innovations introduced sinceradio-broadcast-receiver manufacturing began. Somewere worthwhile and contributed to the development ofthe art, but many were only short-lived gimmicks.

All early radio receivers employed headphones. How-ever, the need for greater sound output soon resulted inattaching horns to telephone-type receivers. These werefollowed in 1922-1924 by cone-type speakers such asthose made by Western Electric and Farrand, which em-ployed cones attached to movirug armatures. In 1924Magnavox designed and marketed a balanced armaturemagnetic-type horn loudspeaker.

In 1925 C. W. Rice and E. W. Kellogg of GeneralElectric developed the electrodynamic loudspeaker,marketed by RCA, and in 1931 Jensen put on themarket a dynamic loudspeaker with a permanent mag-net made of chrome steel, the forerunner of the presentAlnico V and ceramic magnets.Some of the early radio receivers employed loop

antennas. Later, in an effort to receive signals fromgreater distances, outdoor antennas of many typescame into general use. As advances were made in tubes,circuit design and loop-antenna design, it became feasi-ble to use loop antennas without too much loss of sensi-tivity. In 1939 loops came into general use, and some re-ceivers appeared on the market with permeability-tuned loops. In 1950 the use of ferrite-rod antennas in-stead of loops was proposed, and gradually this type ofantenna, the loop-stick, replaced conventional loops.

Early receivers all employed battery operation sincetubes with ac-operated filaments were not available.Then, in 1924 the Philadelphia Storage Battery Com-pany marketed "B" battery eliminators which came intowide usage. Shortly thereafter "A" battery eliminatorswere developed; these also gained wide public accept-ance. In 1926 Zenith built a receiver with both "A" and'B" battery eliminators built in as an integral part of thereceiver. The wide usage of the ac receiver followed themanufacture in 1926 of tubes with filaments which

could be operated on alternating current. Since therewere many areas in the country where only dc power wasavailable, the present day ac-dc circuit was developedby R. Weurfel of International Radio to meet this need.This was first marketed by International Radio in 1931,aind by 1935 about 20 per cent of the total sets madewere ac-dc.

In 1939 portable receivers using battery tubes with1.4-volt filaments became popular and ac-dc-batterysets appeared on the market. One of the outstanding de-velopments of 1940 was the miniature receiver whichweighed less than five pounds and which was poweredby readily-replaceable batteries. Further attempts atminiaturization resulted in a pocket radio employingsubminiature tubes and especially developed conikponents. One of the first of such sets was produced byBelmont late in 1946.

In 1952 the use of printed circuits employing a dip-soldering process was extended to small radio receivers.These steps along with the use in the laboratory of tran-sistors in radio receivers for the first time high-lighteddevelopments in that year. In 1954 Regency marketedthe first transistorized radio.Over the years since the early twenties there have

been many other innovations-all-wave receivers, in-cluding the "weather" band, "spread-band" receivers,AM-FM receivers and "Fremodynes."20 Some of thesereceivers employed IF amplifiers with adjustable selec-tivity, automatic bass boost, noise limiters, tuning eyesand inverse feedback. There have been big tuning dials,little tuning dials, round dials, long dials, short dials, nodials, push buttons and automatic tuning.

These and many other innovations, together with thecircuit developments previously described, have resultedin the sale of over 300,000,000 broadcast receivers at afactory price of about $8,000,000,000, in the UnitedStates to the end of 1960.21

20 "Hazeltine Fremodyne FM circuit," Tele-Teck., vol. 6, pp. 41J85-86; December, 1947.

21 Paul Stone, Ed., "Television Factbook," Triangle Publications,Inc., Radnor, Pa., Spring/Summer ed., p. 28; 1961.

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