Development of video cameras and recorders forlightweight television production

K.H. Barratt, B.Sc, C.Eng., M.I.E.R.E., M.I.E.E., and T.Morita, B.E.

Indexing term: Television

Abstract: The early development of broadcast television equipment for professional use was constrainedby the need' for the best possible technical performance for a market that was limited in its extent. Thusvideo cameras and recorders were expensive, technically complex, bulky and had high power consumption.During this period the use of such equipment was almost exclusively restricted to broadcasters. Gradually,however, the new video technology was increasingly used in institutional and consumer applications. Initiallythe technical performance was limited to obtain equipment that was low-cost, simple in operation, portableand of high reliability. The mass production of precision components was an essential ingredient in meetingthese objectives. As the technology improved so did the performance of the equipment until it was sufficientto meet the requirements of professional broadcasters in an important respect, which was in the obtainingof an immediacy in news gathering, which was impossible with 16 mm film. The rapid growth of ENG (elec-tronic news gathering) provided a strong impetus to the development of a new generation of professionallightweight video cameras and recorders. The experience gained with such products in turn was a majorinfluence on the ability to produce cameras and recorders which had all of the operational advantages of theearly lightweight equipment, but with little or no compromise in performance. Together with the ingenuityof the professional broadcaster the latest equipment is generating an apparent revolution in the techniquesof television field production.

1 Introduction

What may be seen historically as a natural technologicalevolution has usually been a mixture of accident and design.This is particularly true of the development of lightweighttelevision production equipment for broadcast use. Indeedonly very recently has a clear purpose emerged between bothmanufacturers and broadcast users to take advantage of thelatest equipment in the most logical way. In this paper thebackground to this phenomenon is explored from the positionof one manufacturer. It is hoped that the authors may beforgiven for a somewhat parochial overview, as they do notfeel qualified to give a totally balanced historical perspective.

It first seems necessary to define what is meant by light-weight television production equipment in the context ofbroadcasting. At the lowest level it may be a single portablevideo camera and associated portable VTR, used simply forthe obtaining of location material for subsequent editinginto a studio production. At the other extreme it couldcomprise a complete outside broadcast vehicle, with say fourcameras and associated vision and sound mixers, and withtwo VTRs having sufficient space for a complete productioncrew. In both cases the quality of performance, small sizeand low power consumption of the new cameras and VTRsenable a mobility and flexibility that is increasingly attractiveto the broadcast user.

2 Historical prelude

2.1 Invention of the practical VTRAny consideration of the development of television pro-duction equipment must include the invention of the quadru-plex VTR by Ampex in the mid 1950s. Although it was large,expensive and complex in operation in its first realisation,it nevertheless was the beginning of a revolution in televisionengineering operations, and all further developments havebeen strongly influenced by it. Out of the possible recordingformats considered, the principle of transverse recording on2 in wide tape was used as being the most technically feasibleat that time. This enabled the very high relative speed of thevideo heads to the tape, necessary for the recording of very

Paper 2057A, first received 5th April and in revised form 28th June1982The authors are with the Sony Broadcast Ltd., City Wall House,Basing View, Basingstoke, Hants. RG21 2LA, England

high frequencies, to be obtained, while at the same timeallowing a manageable tape speed through the recorder. Asis now well known this was achieved by mounting four videoheads on a head wheel rotating perpendicular to the tapemotion, each head being switched into operation as it beganto scan the tape. The resulting magnetised tape tracks werealmost transverse to the tape edge.

2.2 Development of helical VTR as institutional equipmentThe effect of the release of the quadruplex VTR on companieslike Sony, whose major concern then was with consumerequipment, was how to use the new video recording principlesfor nonprofessional applications. From 1958 a basic studywas started the objective of which was a recorder whichdid not require expert operation, and which was about onetenth of the size and cost of the Ampex VR1000. The keytechnologies identified as being relevant were the non-segmented helical scan principle and the use of semicon-ductors. In the nonsegmented helical recorder a completetelevision field is recorded for each scan of the video head.This is made possible by the wrapping of the tape round arotating head drum. At that time a narrow video bandwidthand a use in closed-circuit applications were further necessaryrestrictions. The resulting product, a PV-100, used an 8 cmdrum with 2 in tape in a table-top version to obtain a videobandwidth of 2.5 MHz, and had a playing time of 1 h for the525/60 standard. At 60 kg it was still hardly a lightweightrecorder. Nevertheless, between 1963 and 1967 some 1000units were sold, including in-flight entertainment systems,which gave valuable experience in tape duplication and inter-change.

The next step, starting in 1962, was seen to be the develop-ment of a video recorder which could be hand carried; theaim being a much less expensive VTR for the home. Herea simpler mechanism was required using a single-motor trans-port, and among ideas experimented with for the homeVTR development was the use of skip-field recording — i.e.only one field out of the two that make up a frame was tobe recorded. The resulting CV models had an 11 cm drumdiameter for 525/60 systems (13 cm for 625/50) and twoheads scanning \ in wide tape, again with a playing time of 1 h.From 1965 to 1972 the main area of application was in theinstitutional market — education, medical, business andindustrial use — rather than for home entertainment.

From 1969 an AV series of models were introduced which

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were similar to the previous CV type, the raison d'etre beingthe collaboration with other manufacturers to obtain the firstnational VTR standard obtained by compromise: the EIAJ-1Japanese standard format which confirmed the position ofinstitutional video. Subsequently portable and editing versionswere developed which greatly contributed to the expansionof VTR applications. The experience with the \ in VTRsuggested an enormous potential demand for the video taperecorder in various fields, in which ease of operation was akey factor in turning this potential into reality. Coincidentallyat that period colour television was just becoming popular.Therefore a development programme was initiated for whichthe target was a cassette recorder having good quality colourpicture and bilingual or stereophonic sound capability. Toachieve this demanded the development of improved tapes(chromium dioxide), recording heads (single-crystal ferrite)and extensive development and use of integrated circuits.Equally important was the major improvement made in theaccuracy of machining mechanical components, in particularthe video head drum. From the beginning reliability wasperceived as being of prime importance because of the aimfor nonexpert operation in a wide range of environmentalconditions. The outcome was the well known U-matic, firstreleased in 1971, and still being sold today. In this producta video recorder was achieved which could be operated byanybody, effectively becoming part of the office furniture.This was made possible by excellent tape interchangeability,very high reliability, reasonable cost and the ease of tapeduplication. On the manufacturing side this was only accom-modated by developing the means of mass producing such acomplicated machine. There the position may have remained,apart from a yet unfulfilled ambition to create a genuineVTR for home use. However a development was to occur,which was totally unforeseen, when CBS News in the USAbegan to use U-matic recorders and video cameras to obtainan immediacy in news coverage impossible with the mediumof film.

2.3 Transition of U-matic into professional ENGIn the colour-under recording method adopted for the U-matica stable colour picture could be obtained on a picture monitorwithout requiring a reduction in the basic timebase error,but such an output would not meet broadcast signal timingstandards. However, the newly invented digital timebasecorrector removed this problem, and the U-matic became acentral part of the new electronic news gathering operations(ENG). Forthwith, new versions were produced which weremore suitable for broadcast applications, but which didnot have any fundamental technical differences.

However, although there was great interest in the appli-cation of ENG in countries whose television was based on 625lines per picture and 50 fields per second the performanceof the multistandard U-matic was inferior in this system tothat in the 525/60 standard, such that it was widely regardedas unacceptable for broadcast purposes. The study of thesolution of this problem requires some analysis of the U-maticprinciple [1].

The colour video signal is recorded on the tape havingbeen separated into two components: frequency-modulatedluminance and amplitude-modulated chrominance, the latterhaving been down converted to lie below the luminance FMspectrum. In this way the luminance also acts as a high-frequency bias signal for the chrominance. The respectivecarrier frequencies and band shapings are so determinedthat luminance and chrominance may share the passband ofthe head-tape system, without being distorted or interferingwith each other. The passband of the head-to-tape systemoriginally deemed to be achievable, although sufficient for

the 525-line NTSC signal (bandwidth 4.2 MHz) is less satisfac-tory for the 625-line Pal (bandwidth 5-5.5MHz). Further-more, because in the U-matic a complete television field isrecorded for a single video-head scan, the video head to tapespeed is slower for the 50 fields per second system comparedwith the 60 fields per second system. This further mitigatedagainst the recording of high video frequencies.

The advantage of choosing common carrier frequenciesfor both 525/60 and 625/50 systems, although permittingmultistandard operation, was seen to be less important thanobtaining better quality for the latter system in broadcastENG use. Furthermore, subsequent progress in video recordingtechnology had enabled higher frequencies to be recorded.In fact using higher recorded frequencies was the most effec-tive way to improve the picture quality. Figs. 1 and 2 show theoriginal U-matic frequency allocation and the modificationsto the 625/50 system. To achieve the latter, however, requiredseveral new developments. First, to expand the high-frequencyrecording capability a narrower head gap was needed, butthis usually not only means lower sensitivity, but also is moredifficult to make. From accumulated manufacturing experi-ence heads with gaps as low as 0.5 jum could be made, whichenabled higher frequency recording to be obtained. Oncethe decision was made not to use the U-matic multistandardformat for 625/50 broadcast ENG use it was possible toobtain other improvements. For example the lower videohead drum rotating speed of five sixths of that of 525/60standard when combined with a fixed tape speed, meantthat if the guardband for 60 Hz systems was satisfactory atabout 40jum, it would be excessively large for 50 Hz systemsat about 80/um, i.e. almost as large as the track width.Increasing the track width from 85/im to 125jum for 625/50systems allowed a 3 dB improvement in signal-to-noise ratioto be obtained.

0 1 2 3 u 5MHz

Fig. 1 Frequency allocation of original multistandard U-maticsystem

0 1 2 3 4 5 6 7 8

Fig. 2 Frequency allocation for U-matic H system for use in broad-cast ENG in 625-line 50 fields per second systems

IEEPROC, Vol. 129, Pt. A, No. 7, SEPTEMBER 1982 437

A number of other improvements were incorporated, theoverall result being a substantial improvement in performanceto the point where the quality was satisfactory for broadcastENG purposes in countries using 625/50 systems. The new,sometimes called 'highband', U-matic fomat was adoptedby the EBU as the recommended VTR format for ENG [2].

2.4 Move towards full professional helical VTRIn the early to mid-1970s, then, there was increasing recog-nition that developments in technology were likely to makethe quadruplex recorder obsolescent, and there was increasingpenetration of the 3/4 in U-matic format, albeit in a lower-quality form for ENG. There began to appear rumours, ideasand some models of helical machines based on 1 in widetape. In some cases it was clear that the intention was toproduce a lower grade of performance than for full broadcastuse, but for others, the goal was a broadcast recorder. Inparticular, it was recognised that the techniques of minia-turisation and mass production, which enabled high-precisionproducts to be made with high reliability and low cost, werenot only valuable for the consumer and institutional markets,but also for the professional models. Hence the supposedproblems of the helical-scan recorder were no longer insur-mountable: timebase errors could be made negligible byadvanced tension control and digital timebase correction,accurate tracking could be guaranteed by production tech-niques acquired through experience with nonprofessionalVTRs, and finally the size of the video head drum could bekept within manageable proportions by advanced head andtape designs. It was perceived that strong advantages werenecessary to convince broadcasters to change formats, particu-larly from such a well established one as that of the quadru-plex recorder. With a nonsegmented format these were seento be low operating costs, and the availability of more oper-ational features. The former accrued from smaller machinesrequiring less floor space, the use of narrower tape givingreduced tape and storage costs, and lower power consumption.The latter included the availability of pictures for editingpurposes at all speeds, including still, from fast forward torewind, the possibility of broadcast slow-motion effects bydistorting the video head scan to keep the head on track attape speeds other than normal, and the more readily achiev-able genuinely portable recorder for location purposes.

The broadcast fraternity in the late 1970s, becameincreasingly alarmed at the growing number of possible 1 informats, causing them, through the SMPTE [3,4] in theUSA, and subsequently the EBU in Europe [5], to attempta rationalisation in collaboration with the manufacturers.This resulted in the Type C 1 in nonsegmented format bya merging of the similar Ampex and Sony proposals, and thetype B 1 in segmented format derived by Bosch Fernseh.Now such recorders are a part of everyday broadcast operationin almost all major broadcast countries, and provide the foun-dation for lightweight television production.

2.5 Portable camera developmentThe development of portable video cameras during this periodwas noticeably less dramatic, but hardly less important.The Plumbicon three-tube camera was well established, anddid not have the interchange problem of the VTR. Hence thepace of development was dictated by the manufacturers'capability to meet the requirements of ENG, and a stronglycompetitive industry. The 30 mm and 25 mm Plumbicontubes used in the studio cameras were too large for portableuse, and so 17 mm tubes were introduced.

However, the stringent demands of registration, cornerresolution and sensitivity were only met by continuous steadydevelopment. The camera portability, power consumption

and reliability were improved by the extensive use of inte-grated circuits. Now the performance of these cameras isvery close to, and it is considered in some cases to surpass,that of its bigger studio brethren. It too is a vital part of thelightweight television production armoury.

This brief historical summary more or less brings thepicture up to the present day, and in the following Sectionswe shall seek to deal in more detail with some of the conceptsbriefly introduced, and to outline some of the newer develop-ments.

3 1 in nonsegmented Type C VTR

3.1 Outline design requirementsThe availability of pictures at tape speeds greatly differentfrom normal play speed demands that a complete televisionfield be recorded in one scan or swipe of the video headsacross the tape. If a transverse scan such as that of the quadru-plex recorder were used the tape would have to be nearly40in wide, which is obviously impracticable. If 1 in tape isused then the video track, of necessity much longer than fora segmented recorder, will have to be inclined to be at asmall angle, of the order of 2—3°, to the tape edge.

For a reasonable size of head drum to be used the tapewill then have to be wrapped round a major part of the drumperiphery. If a single video head is to record all of theactive picture part of the field, and some of the verticalblanking interval, this wrap will approach quite close to360° (in fact about 346°). This leads to the concept of theso-called Q, wrap from the shape of the Greek capital letter.

upper drum

tape exitguide

lower drum

tape entranceguide

video tip

tape reference edge(guided edge)

Fig. 3 Tape wrap in nonsegmented helical type C machine formsshape similar to Greek letter Omega

Now, the actual physical length of the track is determinedby the ability to record high frequencies, which in turn iscontrolled by the head and tape efficiencies in recording andreplaying short recorded wavelengths. It is developmentsin these subjects which have had such a great bearing on thepracticability of the 1 in VTR. For analogue video the useof narrowband FM recording, introduced by Ampex, haslong been recognised as an effective method for simul-taneously reducing the enormous octave bandwidth of thetelevision signal, and the non-linearities associated with ampli-tude modulation. In narrowband FM the first sideband of thecarrier is paramount and the second and higher may beignored. The concept of a carrier frequency is not readilyapplied to television signal modulation, and it is usual to referto rest frequencies representing peak white, black level andsync tips. If the highest modulation frequency to be recordedis added to the peak white rest frequency, and subtractedfrom the black rest frequency, the frequencies obtainedbound the necessary recorded bandwidth for narrowband FM.This leads to a bandwidth, and hence highest frequency, ofsomething in excess of 14 MHz. A video head output willbecome zero at a recorded wavelength equal to the head gap,and so the recorded wavelength at 14 MHz should be longerthan the head gap, which if about 1 jum represents a minimumrecorded wavelength of at least 1.4/um. The required head

438 IEEPROC, Vol. 129, Pt. A, No. 7, SEPTEMBER 1982

to tape velocity is the product of head gap and highestrecorded frequency, giving in this case close to 20m/s. Infact the head to tape velocity for 625/50 systems is of theorder of 21.5 m/s.

To record nearly 301 lines out of a complete field of312.5, leaving 12 lines of the vertical blanking periodunrecorded, requires a track length of about 411 mm (orabout 16 in). With a wrap angle of 346° a drum diameter of134mm (or about 5.3 in) is required.

In terms of tape speed something less than 397mm/sof the quadruplex recorder was sought, and 240mm/s waschosen. With the dimensions given above this fixes the trackpitch to be 214jum, and with the reserving of an adequateguardband of 54 /um this leaves a track width of 160jum.

The preceding summary leads to the major design problemsfor the 1 in helical nonsegmented Type C video recorder,i.e. how to obtain a satisfactory signal-to-noise ratio fromtracks of 160jum in width, while adequately tracing suchnarrow tracks over a length of 411 mm. In addition thetracking needs to be compatible with tape interchangebetween, not only machines of the same make, but alsobetween those from different manufacturers. This interchangeconsideration was of fundamental importance for broadcastusers, and for some time was held to be impossible by theopponents of the Type C recorder. That it was to becomeeminently satisfactory is now also a matter of history. Thetape guiding and tracking accuracy are particularly demandingin a portable VTR, and some of the more detailed designconsiderations in one Type C portable realisation will begiven later, but first a few of the more incidental Type Cdesign considerations will be discussed.

3.2 Editing and slow-motion facilitiesOne of the more powerful and effective operational featuresof the nonsegmented recorder is the ability to produce pic-tures, albeit impaired, in speeds other than that of normalplay. This enables a film moviola approach to editing, withfast shuttling to find a required sequence, and a frame byframe jog facility to find a precise edit point. This last require-ment demands that the best possible picture is obtained whenthe tape is stationary.

normal tape motion

— track on tapehead travel

Fig. 4 Magnetised video track on tape is vector sum of video headand normal tape motions

line sync

The track produced on tape is the result of the vectoraddition of head and normal tape motions. When the tapeis stationary the head traces out a path which traverses twotracks, as shown in Fig. 4. When the head is crossing theguardband, noise is produced, but the picture disturbancemay be minimised by ensuring that the recorded line syncpulses are aligned (i.e. the video head picks up a line syncpulse from the adjacent track at exactly the same positionas it would have done from the original track).

This is achieved as shown in Fig. 5, but, as is seen, resultsin an offset between adjacent tracks of an odd number of half-line intervals. The odd number occurs because there are anodd number of lines in a frame, and in 625/50 systems theoffset is 3.5 lines. At fast shuttle speeds many more trackswill be crossed for each head swipe, but the principle of syncalignment still applies allowing recognisable pictures to beobtained at speeds up to 40-50 times normal play speed.

Having acquired the operational convenience of beingable to recover a picture at all speeds it is desirable thatthe maximum benefit be obtained from it in editing.Increasingly, computer-aided editors are being used whichobtain their reference to the position on tape from a longitudi-nal time code track, containing a digital code conveyinghours, minutes, seconds and the number of frames [6].However, the recovery of this information fails at very lowspeeds (at about 3.3—5% normal play speed). Having foundthe precise frame required visually by jogging, it is thenimpossible to 'mark' this frame time code into the computer-aided editor. To overcome this deficiency vertical intervaltime code (VITC) was developed in which the time code isalso inserted into that part of the vertical interval which isrecorded with the video [6]. This may be recovered by thevideo head at speeds from still up to greater than normalplay speed, giving a more than satisfactory overlap withlongitudinal time code.

Having pictures available at slow tape speeds giving a slowmotion effect, albeit with the noiseband associated with thetrack crossing, it seemed to be a natural extension to attemptto obtain such pictures without the noise. With analoguesignals this can only be done if the guardband is not traversed,which in turn means that the video head must be constrainedto travel along a different path from normal (see, for example,Fig. 4). In outline this is performed by mounting a videohead onto a piezoelectric bimorph which, under the appli-cation of a polarising voltage, causes a transverse movementof the head. To obtain the necessary track-following infor-mation the head is 'dithered' at several hundred hertz, thevariation in RF recovered giving a feedback signal. Suchdithering can introduce low-frequency components into the

bimorphhead tip

tape

Fig. 5 Principle of sync alignment allows minimum picture disturb-ance when video replay head traverses two or more tracks

a b

Fig. 6 Piezoelectric bimorph head arrangements

a Video head mounted on a single bimorph causes the head to tapecontact to be non-perpendicular when the head is displaced in dynamictracking.b With double bimorph and video head carrier the perpendicularcondition may be maintained when the head is displaced.

IEEPROC, Vol. 129, Pt. A, No. 7, SEPTEMBER 1982 439

video output, and more refined systems use a first-orderprediction method, with a smaller amplitude dither beingused to find the final position precisely. Keeping the videohead on one track recovers only one field, and it is thereforenecessary to produce from it the other interlaced field, andalso the necessary subcarrier variation from field to field.This processing is done in the timebase corrector, and pro-duces some impairment, but on balance the performanceis remarkably good, and is regularly used for broadcast pur-poses. Another factor which can cause impairment is thevariation in head to tape contact when the head is movedtransversely.

In Fig. 6a the head is now not perpendicular to the tapewhen deviated, which may result in poor signal recovery.By mounting the head on two bimorphs, as in Fig. 6b, theperpendicular condition may be maintained.

This brief overview has discussed some of the more salientfeatures of the design of a 1 in Type C VTR, and, as earlierindicated, the mechanical realisation of it in the portableform will now be discussed. As the studio machine is becomingthe standard broadcast production tool the portable versionis not allowed any reduction in quality, and yet by definitionit must be light, small in size, rugged and consume the mini-mum power. In the portable therefore, the 1 in Type C formatfaces a tremendous challenge.

3.3 Portable 1 in Type C VTRIn Fig. 7 is shown a schematic of the tape path for a portableType C VTR [7], illustrating the ingenuity required to obtainthe necessary complex functions in a small space.

Particularly vital in a portable VTR is the reduction offriction in the tape transport as, not only does this affectacceleration, shuttle speed and tape life, but it also reducesthe power needed by the take-up motor, which in turn reducesthe size and weight of the battery required. In this machinethe wrap angles and the number of fixed guides are keptto a minimum, and rollers are used where feasible.

To conserve space the guide rollers are positioned in sucha way as to provide the necessary variation in pitch angleas well as the directional changes. The timer roller whichrequires the greatest wrap is placed at the position wherethe largest change of direction is needed.

In these examples we see a fundamental philosophyrequired in a portable design, which is to satisfy as manydesign constraints as possible with a single solution. Theupper video drum can also make a considerable contribution

tension armsguide roller 3 guide roller 2 \ guide roller 1 supply/take-up reels

tapetape timer roller

capstanpinch roller

guidesconfidence head

audio-1/2/3REC/PB head

audio-1/2/3erase head

guide roller Uguide roller 5

inlet /outletguides

video headdrum assembly

Fig. 7 Tape path for one realisation of portable Type C VTR

440

to the friction losses; owing to drum rotation the coefficientof friction can be reduced to 0.1 compared with 0.2-0.4for a fixed guide post, but this may introduce an undesirablesensitivity to transverse disturbances. However, the use ofa rabbet on the lower drum solves this problem completely.This needs to be accurately machined using special techniques,but as a result vertical movement of the tape is virtuallyeliminated, allowing excellent interchangeability. Fig. 8shows the measured vertical movement obtained in exper-iments on several tape support systems.

10 urn

10 urn

10um

8 s

Fig. 8 Comparison of transverse motion obtained with severalmethods for support of tape during travel round drum

a No guide b One support guide at midpointc Rabbet guide

As clearly seen from the Figure, the rabetted drum showsthe least deviation and is obviously the best solution.

To achieve l h of recording it is necessary to mount 9 inreels. To conserve space a stacked reel system is used, whichnecessitates providing a level difference between take up andsupply reels which is greater than that resulting from thehelical tape path. This, with advantage, is placed on thesupply reel side, thus isolating the take-up side from theeffects of uneven tape winding, and the head drum and audiostack from irregularities in reel rotation. The relatively largeseparation between the drum and the supply reel assists in theabsorbing of any fluctuations in the linear tape velocitycaused, for example, by uneven winding or eccentricity inthe supply reel. As the tape is made of what is substantiallya viscoelastic material longitudinal vibrations may be inducedby external disturbances which can appear as jitter or modu-lation noise in the audio signals. In this machine the massesof the guide rollers are chosen not only to minimise frictionallosses, and so-called 'stick-slip' vibrations, but also to dampout these other vibrations in the tape. Fig. 9 shows the resultsof modelling this system for guide rollers, in the shadedpositions in Fig. 7, compared with the alternative use offixed-post guides. The improvement in velocity error above400 Hz is clearly seen.

Many other developments were necessary in servo systems,

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power saving design, and robust yet lightweight constructiontechniques in the full realisation of a portable Type C 1 inVTR, which unfortunately cannot be covered in such a sum-mary. It is hoped, however, that some indication has beengiven of the necessary interaction of a number of disciplinesto achieve a performance widely regarded as impossible afew years ago.

4 Development of portable colour video cameras forbroadcast use

4.1 Influence of ENGThe development of the latest lightweight cameras has beeneven more strongly influenced by the penetration of ENGinto the broadcasting domain. Before ENG shoulder-supportedbroadcast cameras were slimmed down versions of studioversions using 25 mm Plumbicon tubes, and were relativelyheavy and unwieldy. The much lighter institutional camerasdid not have the required performance. Hence new cameraswere required, and the RCA TK76 was the first realisationof a camera, suitable for ENG use, based on the use of 17 mmPlumbicon tubes. CBS Laboratories described the developmentof what was called the Microcam, split into two units compris-ing, respectively, a head block and a backpack in which thebulk of the video processing was done. The use of two unitsseemed to have practical limitations, and be a source ofpossible unreliability due to the cable interconnection. How-ever, it indicated that light weight and good technical qualitywere not necessarily contradictory, and a number of camerashave subsequently confirmed this. Within Sony a target wasset for a totally self-contained camera with the requiredtechnical performance, but with a weight of not more than10 kg including lens. Such an objective could not have beenmet without the excellent collaboration and contributionfrom the lens manufacturers - Fuji, Canon and subsequentlyAngenieux and Schneider - towards high-quality small light-weight lenses with extensive zoom ranges and internal irisand zoom motor control. Additionally, new designs of theoptical splitter block were essential to the improved perform-ance and smaller size. By using glass of a higher refractiveindex, smaller critical angles of total internal reflection couldbe obtained within the prism block (Fig. 10). With the moreupright surfaces made possible (that is more nearly normal

Or

-20

-40

o

*-100

-120

audio

videofixed guide

posts at ^inFig.7

video \ .

100 1000frequency, Hz

roller guidesat liinFig.7

10000

Fig. 9 Use of roller guides in shaded positions of Fig. 7 gives ben-eficial improvement in velocity error compared with use of fixed-postguides

IEEPROC, Vol. 129, Pt. A, No. 7, SEPTEMBER 1982

to the incident light) a shorter block could be made with ahigher transmission factor and a wider acceptance angle.Again this made a major contribution towards low weightand compactness.

Fig. 10 Typical optical prism splitter block

Use of high-refractive-index glass allows a shorter block with a highertransmission factor to be obtained.D = dichroic, F= trimming filter, T = taking lens

4.2 Anti-comet-tail tubeFurthermore, extensive development of the 17 mm Plumbicontubes was a vital factor in such a camera. One factor whichwas originally thought to be a major restriction, i.e. thedifficulty of manufacturing a 17 mm tube with anti-comet-tailcharacteristics, was solved by the ingenious development byNHK and Hitachi of automatic beam optimisation. If thebeam current is set at a low enough level to maintain electron-beam focus, and give a reasonable tube life, then it will beinsufficient to fully discharge the target on intense highlights,causing blooming and a comet-tail effect if the camera ispanned. In automatic beam optimisation the beam currentis increased during these highlights (by up to more thanten times if necessary), thus providing sufficient current fortarget discharge. Without this expedient it would be necessaryto reduce the iris size by more than three stops to be ableto discharge the highlights, thus greatly reducing the availablelight from outside the highlights. The use of automatic beamoptimisation has been so successful that an anti-comet-taildesign for the 17 mm tube is now thought to be largelyunnecessary.

4.3 Circuit developments in the improvement ofsignal-to-noise ratio

With the improved lenses, splitter blocks and tubes manyof the factors necessary for the lightweight, high performancecamera were now available, but ENG presented a tremendouschallenge in obtaining the best possible sensitivity as, in manycases, there is neither the time nor the opportunity to provideextra lighting. With given tubes and optics the burden ofobtaining high sensitivity is thrust on the head amplifier,and many years of semiconductor development were drawnon to produce an FET tailored to the requirements. As iswell known, apart from having a head amplifier with lowintrinsic noise, a low input capacitance has a major bearingon the signal-to-noise performance, but the acquiring of thislow capacitance usually conflicts with obtaining an adequatemutual conductance. Without the latter a low gain-bandwidthproduct for the head amplifier output could make the secondstage noise more important.

Conventionally, to achieve a better gain-bandwidth per-formance, and hence a reduced effect of the head amplifiernoise, an inductance known as a percival coil is mountedbetween the tube output and head amplifier. However, thisin turn can introduce its own stray capacitance, thus mitigat-

441

ing against its beneficial effect. If a low-input-capacitancedevice can be made there can be advantages in dispensingwith the inductance, and in mounting the head amplifierdevice as close as possible to the tube output. This was infact achieved with an FET with an input capacitance ofabout 7pF and a mutual conductance of 25 mS, giving as afigure of merit agm/Cin ratio of 3.5 nS. The effect on sensi-tivity was remarkable, allowing a luminance signal-to-noiseratio of 51 dB, and a sensitivity of f5 at 2000 lux from asurface of reflectance of 90% at 3200 K. This enabled 18dBof gain enhancement to be used, with light levels as low as20 lux, while still obtaining good quality pictures. In sucharduous conditions noise performance is more critical thanresolution, and with benefit, some bandwidth shaping can beused to further improve the signal-to-noise ratio.

Inevitably, integrated circuits play an important role inthe reduction of size and power consumption and in theimprovement of reliability, and increasingly special-purposeintegrated devices (e.g. sync generators) are used.

Putting all these factors together enabled the productionof a camera of 5.9 kg in weight (excluding lens), a powerconsumption of 22 W, and a centre resolution of 500 lines,together with the previously mentioned sensitivity and signal-to-noise ratio, all within an easily carried package. However,all of this is of little value, particularly in ENG use, if it isdifficult to operate or requires frequent adjustment of controlsother than those pertaining to the lens. Much of the designis therefore given over to what might be termed ergonomicfeatures, a catalogue of which is not relevant to this paper,except perhaps in a mention of one which illustrates howfamiliarity with an older design often impedes acceptance ofnew ideas.

During the development of this camera it was conceivedthat a low centre of gravity would have a stability advantage,and this was achieved to a large extent by a design that fittedthe shoulder. However, in the early days operators used toa simple box shape expressed some reservations, but withoperator experience it was to become accepted andincreasingly universal.

It is not yet possible to design a camera which can copewith the enormous range of colour temperatures which maybe met, so that it is usual to provide a filter wheel whichcan be operated to insert filters which centre the cameraoperation on 3200 K or 5600 K. In these circumstancesit is necessary to be able to rapidly colour balance bothwhite and black, without losing these settings when thecamera power is switched off. This facility is automatedrequiring only 2 s to complete, and in the case of white bal-ance only about 20% of white is needed in the total picturearea. Having performed this operation the settings are storedin a digital memory powered by a small internal rechargeablecell, which in turn is charged by the main battery. Removalof the main battery supply then does not destroy the setting,which is retained for a considerable period. Of course thenone is more concerned with the memory of the camera oper-ator rather than with that of the camera!

4.4 Development of a true EFP cameraAt this stage a camera was now available which was excellentfor ENG use and very good for electronic field production(EFP). The temptation was obvious — was it possible tomake a camera that was excellent for EFP or even for studiopurposes? The major areas requiring improvement wereresolution and registration, particularly outside the centralzone. Without question, to improve the former one neededto seek improvement in the tube, and this was possible if thediode gun Plumbicon tube described by Philips [8] couldbe manufactured in the 17 mm size. Matsushita were the first

company to make this available, followed subsequentlyby Philips. There are a number of aspects to this tube, themost important of which is the replacement of the triodegun with a diode form, and the use of an accelerating lensfor electronic focusing.

With a triode gun the cathode, grid and anode form a lenswhich causes a focusing or crossover between the grid andanode (Fig. 1 la).

G

0V -40V

A

300V

\0V\

\

30V

Fig. 11 Comparison between diode and triode guns

a A conventional triode gun produces strong focusing, and henceinteraction of the electrons, in the region of the grid,ft In a diode gun there is a very much smaller interaction, althoughthe resulting beam is more divergent.

The strong interaction of high-energy electrons in thiscrossover region cause a proportion of the electrons to havean excessively high axial velocity. The consequent increasein beam impedance reduces the speed of target response,i.e. increases the lag. In the diode gun (Fig. lib), with amuch lower anode potential the electron energy is far less,and the interaction is reduced because there is no crossover.Thus the axial electron velocity distribution is much closerto that expected from the Maxwellian distribution of thecathode emission, and an improved lag characteristic isobtained. An apparent disadvantage of the diode gun is themuch more divergent beam obtained at the anode whichimplies a more difficult focusing problem. However, theconstraining factor is the magnification of the anode apertureat the target, which is proportional to the square root ofthe ratio of the initial potential to the final potential. Withthe low initial and high final potentials of the diode anodeand accelerating lens, respectively, the ratio can be madesmaller than in other tubes, which in turn reduces the magnifi-cation, leading to a significantly sharper beam. Against this,for various reasons a high final potential demands accurateconstruction of the electron lens, which necessitated theappropriate constructional technology to be developed beforethe 17 mm diode gun tube could be a practical proposition.

With such tubes a centre resolution of 600 lines is achieved,and, as indicated earlier, to make full use of this better controlof registration is required. First the necessary horizontal

442 IEEPROC, Vol. 129, Pt. A, No. 7, SEPTEMBER 1982

and vertical correction signals (barrel, pin cushion and trap-ezoidal) are provided to align the red and blue tubes with thegreen tube. However, these second-order corrections are lessprone to drift than the overall centring of the three images,and so this is the process which most benefits from auto-mation. This has been achieved requiring, in the set up, normalpictures with a measure of vertical and horizontal information.A maximum duration of 10 s is required for the automaticcentring. Again the settings are stored in digital memorywith power back up from the rechargeable cell. Experienceobtained with earlier cameras has led to further improvementsin the head amplifier design, giving a signal-to-noise ratioof 55 dB (which makes the 18 dB gain option even moreuseful) and a lower weight of 5.3 kg without lens. Now thiscamera meets the full broadcast standards of many organis-ations, and is becoming a regular part of EFP operations,when equipped with a larger viewfinder.

It is hoped that the preceding discussion has given someidea of how the latest video recorders and cameras havebeen developed from what may be regarded as unpromisingbeginnings and yet with a steadily improving quality to thepont where there is little or no compromise in performance.This process is continuing, but already the lightweight, econ-omical and compact form, together with the technical quality,has made the lightweight revolution a reality.

5 Future developments

What might we expect in the future? An extensive use of thecrystal ball is not only possibly dangerous for the futurereputation of the authors but would demand a considerablylonger paper. However, some attempt will be made.

First we can expect a consolidation of accrued experienceof both manufacturers and users in second-generation equip-ments. This has already occurred in the broadcast U-maticfor ENG, where lighter and more rugged portable versions [9]have been produced, and more recently in the studio model.In the latter case a complete redesign of the transport hasenabled a reduction in tape path friction, which means thecassette tape can be safely moved in fast forward or reversemodes while loaded, i.e. the tape remains wrapped aroundthe head drum. Hence pictures can now be obtained in fastshuttle. Front loading of the cassette is provided in a shapethat permits mounting in a 19 in rack without the spacenecessary for the earlier top loading. Complete editing facili-ties are provided on the front panel, which may be remotelylocated. Dynamic tracking versions are also available. In theType C 1 in recorder we may expect lighter, smaller, moreergonomic versions with improvements in both video andaudio quality. Increasingly microprocessors will be used toobtain better performance in sophisticated control systems.

Attempting to move forward from this stage requires agreater degree of speculation. Partly as a result of digitaltelevision studies there is increasing interest in reducingthe impairment caused by the bandwidth sharing of luminanceand chrominance in the composite signal, whether NTSC,Pal, or Secam. For ENG this has led to the development ofcombined camera and VTR packages, such as the SonyBetacam or the RCA Hawkeye. In these units it is possibleto derive separate luminance and chrominance signals, andrecord them individually on tape. There are, however, substan-tial differences between the proposed methods. In the authors'view it is of prime importance that the new equipment shouldnot only produce better results, but should be flexibly inter-changeable with the existing ENG equipment, i.e. the progressshould be an evolutionary not a revolutionary process.

As described above the interest in component rather thancomposite recording arose out of digital television studies,

and in particular experiments in digital video recording.It is of interest then to consider how the digital VTR willinfluence the utilisation of the 1 in Type C equipments.

It is clear from user surveys that the increasing confir-mation of the technical quality, reliability and operationalflexibility of Type C machines has in turn increased thedemands placed on the digital machine. Thus, while wishingto have the better multigeneration capability of a digitalVTR, little or no compromise is expected in size, powerconsumption, cost or operational features. Additionally,study groups within the SMPTE and EBU are pursuing inter-national format standards in collaboration with manufacturers.The original euphoria produced by the first demonstrationsof experimental digital VTRs has been replaced with a relativecalm in which the many problems are progressively beingsolved, hopefully leading to a format that will not becomeobsolete shortly after its introduction. Thus it is to beexpected that several years will elapse before the digitalVTR will be readily available.

In cameras it seems likely that the 17 mm Plumbicontube will continue to be developed such that 25 mm and30 mm tubes will become less and less important. Alreadyprogress in the other direction is being seen with 13 mm oreven smaller tubes being suggested for ENG applications.However, three-tube colour cameras have for so long beenregarded as the only satisfactory method of obtaining pro-fessional quality pictures, that the designers dream of a single-tube colour camera has generally been considered impossiblefor broadcast use. Steady progress over the past nine yearsis gradually eroding that view, and very recently a highbandSaticon Trinicon tube has been incorporated into a cameraby Sony for lightweight ENG use. At 2.95 kg without lensit offers an unparalleled manoeuvrability with the powerfuladvantages of being entirely free from registration and grey-scale tracking errors. To obtain satisfactory ENG qualitymany developments have been necessary since this tube wasannounced in 1973. The colour performance is obtained bymounting an RGB striped transparent filter in front of thetarget, and the width of an RGB triplet has been progressivelyreduced from 54/urn to 27 jum. As by careful attention to thetransparency of the filter stripes they have equal transmissionto achromatic light at 3200 K the luminance resolution isthen related to a 9/im stripe. The progress of line scanningeffectively converts the tube output to a luminance basebandsignal with chrominance superimposed on a 6 MHz carrier.To take advantage of this increasing intrinsic resolution hasrequired many other factors to be considered, as describedin Reference 10.

Finally, in conclusion, the concept that broadcast televisionnecessitates the use of heavy, bulky equipment which needstechnical experts to operate it is so rapidly being dispelledthat it is difficult to predict even a few years ahead. Theimpact of the new -equipment on programme productionmay seem to be revolutionary, but as is usually the case therevolution is based on steady progression from unpromisingbeginnings.

6 References

1 MORITA, T., and TAKANO, M.: 'An upgraded 3/4 inch videocassette recorder'. 10th International Television SymposiumRecord, 1977, Session E, Section E-ll

2 'ENG helical-scan video cassette system using 19 mm (3/4 inch)tape (U-Matic H format)'. EBU Technical Document Tech. 3233-E1st Edn., July 1980

3 FIBUSH, D.K.: 'Proposed SMPTE Type C helical-scan recordingformat: A sub-committee report' in 'One inch helical videorecording - a collection of papers presented at the 12th SMPTEtelevision conference'. 1978, pp. 8-25

4 ALDEN, A.E.: 'The development of national standardisation

IEEPROC, Vol. 129, Pt. A, No. 7, SEPTEMBER 1982 443

of the one inch helical video tape recording systems' Ibid, pp. 26-29

5 'Helical-scan television recording on 25.4 mm tape'. EBU TechnicalInformation Sheet 7,1st Edn., Feb. 1979

6 'EBU time-and-control codes for television tape recordings (625-linetelevision systems)'. 3rd Edn., April 1982

7 MORIZONO, M.: 'Technical description of Sony's portable oneinch machine, the BVH-500: First discussion of its technical par-ameters'. Ibid. pp. 37-60

8 VAN ROOSMALEN, J.H.T.: 'A new concept for television cameratubes', Philips Tech. Rev., 1980, 39, pp. 201-210

9 BARRATT, K.H.: 'A lightweight portable VTR for ENG use'.11th International Television Symposium Record, 1979, Session1B1, Section 7

10 KUBOTA, Y., and KAKIZAKI, T.: 'An ENG camera using a singlepick-up tube'. International Broadcasting Convention, IEE Conf.Publ. 191, 1980, pp. 38-41

Mr. K.H. Barratt is a graduate of ReadingUniversity. He joined the BBC in 1961as a direct entry engineer in televisionstudios. From 1962 to 1966 he workedin the BBC Designs Department, pre-dominantly on UHF television projects.In 1970 he joined the IBA Experimental& Development Department, and wasinitially engaged in studies for the useof digital computers for the monitoringof UHF television transmitters. In 1973

he became the manager of the DICE (digital intercontinentalconversion equipment) project in the Video & Colour Section,and continued in the project leadership of digital televisionstudies. He has been the Technical Director of Sony Broadcastsince its formation in January 1978.

Mr. T. Morita graduated in electricalcommunications from Waseda Universityin Tokyo, and in 1956 joined the SonyCorporation. He was initially engagedin the development of transistorisedaudio tape recorders and other audioproducts. In 1958 he became a memberof the project team when the companystarted the development of video taperecorders. Since then he has beenassociated with video tape recorder

developments, including several years of technical supportin the USA, initially when the first nonbroadcast VTRwas launched in 1963, and subsequently with U-matic in1971. Since 1978 he has been based in the UK as AssistantTechnical Director of Sony Broadcast.

International Broadcasting ConventionProceedings of the International Conference on International Broadcasting Convention, held at theMetropole Conference Exhibition Centre, Brighton, UK, 18-21 September 1982. Organised by theElectronics Division of the Institution of Electrical Engineers in association with the EEA, IEEE, IEE,IERE, Royal Television Society and the Society of Motion Picture and Television Engineers.

SESSIONS

Broadcasting Technology for the Future. Origination Equipment. TV Transmitters and Transposers.Radio Transmitters. Higher Definition Television. Recording. Satellite Broadcasting. Television Links,Including Fibre Optics. New Services. Receiver Technology. Measurement Technology. Sound Broad-casting. Digital Coding Standards.

Selected Papers

Television cameras — the sensor choice. An experimental wind and solar power 4 channel UHF trans-mitting station. New directions in high-power transmitter design. System concepts in high fidelity tele-vision. Development of ultra wide band video recorders. The use of satellites in modernizing and expand-ing international high-frequency broadcasting. From analogue to digital links - the transition period.Planning VHF radio services with special reference to the ITU Conference and extended band. Progressin the development of UK level 4 teletext. Improvement of picture quality by digital processing indomestic receivers. Automatic broadcast equipment test system. Latest developments in radio broad-casting sound mixing techniques with special reference to self-operation and engineer driven applications.Worldwide digital video and audio standards — on the threshold? Sampling structures for solid-statesensors. An all-solid-state 200 W UHF television transposer.

86 papers, 344 pp., 297 x 210mm, soft coversISBN 0 85296 263 0 1982.IEE Conference Publication Number 215UK £28.00, Americas $64.00, elsewhere £32.00.

444 IEEPROC, Vol. 129, Pt. A, No. 7, SEPTEMBER 1982