Ls Digirol Television New? Moybe Not, but Boird's Television System Wos Certoinly O Pig in O Poke: Wosn't It? Don Mcleon Hos Some New Evidence
Total Page：16
File Type：pdf, Size：1020Kb
HISTORY Digitol vi sions ls digirol television new? Moybe not, but Boird's television system wos certoinly o pig in o poke: wosn't it? Don Mcleon hos some new evidence. he much-hailed start of digital cally-scanned television - viewed for focus, lcd, digital data recorder and television may not be quite the decades with disdain - will then, I computer interflace. giant leap you think. Digital tele- believe, sit alongside electronic ana- We should neither revere nor ridicule vision broadcasting - converting pro- logue tv as an equally valid engineer- historic technologies - they are merely gramme distribution to a fully digital ing solution to 'television'. the best solutions available at the time, environment - is just one small step in Fig. 1. a steady 'technology refresh'. Mechanically-scorned tv This engineering process started over Today though, most of us have accept- A new view on the past twenty years ago and will continue for ed a view originating from the BBC To be objective about early television, many years yet. Fully digital television, back in the late thirties. We think of what we need - and have not had up and digital scanning standards, will John Logie Baird's low-definition tele- until now - is evidence. Without it, his- emerge when the flat-screen tv replaces vision system of the twenties and early torians have had to rely on written or the cathode-ray tube in our television thirties as somehow 'wrong', and of eyewitness accounts, some of them sets. Then, analogue tv and all its trap- electronic television as being 'right'. made decades after the event and most pings, such as PAL (or NTSC) coding, Part of this comes from 'technology of them dismissive and derogatory. sync pulses, colour bursts and interlace, arrogance'. In the sixties, the BBCI ln 19962 and early 1998, hard evi- will be history. seriously questioned Baird's achieve- dence turned up in the form of home That digital future, with our current ments because no part of his technolo- video recordings made from BBC tv analogue tv obsolete, will give us a gy was in sixties' television systems. programme transmissions in the thir- new view of television's engineering But, today, nothing directly of sixties' ties. Until then, the entire mechanical- history. The early years of mechani- technology is in a nineties' consumer ly-scanned era of television was digital video camcorder - with its chip thought to be devoid of any such Donald F Mclean BSc(Hons) CEng FIEE sensor, image stabilisation, digital auto- recording. These digitally restored .l t60 ELECTRONICS WORLD February 999 HISTORY Fig. t. Mechanically-scanned television is in use today by the military. ln airborne reconnaissance, the high-resolution television cameras on RAF Tornado GRIA aircraft use mirror' drum scanning. Coincidentally the aspect ratio is similar to that of Baird's 3?-line standard, (from Crown Copyright original) Fig. 2. One of the many consumer devices that recorded audio onto aluminium discs. On more than one occasion, machines such as this were used by viewers to record the video signal of the BBC's SoJine broadcasts, recordings now challenge the long- exploited their existing broadcast established view. infrastructure to the full. To understand why this is so, let us fast rewind to just after Baird's exper- No recordings? If the BBC or the imental period of the years around Baird Company ever attempted record- 1930. ing their programmes, there is today no record of it. Fortunately for us, a few BBC chooses Baird's 3O-line system. enthusiastic viewers made crude video Fig. 3. With no ln 1932 the BBC chose Baird's 30-line recordings on their domestic audio different speeds, the starting point was clue as to date or standard for its television service, equipment, Fig. 2, from BBC broad- that the signal matched Baird's 3Oline authenticity, one despite higher definition being avail- casts. They had been inspired by video standard. Without a date to go of the discs has a able. It was chiefly the lack of suitable Baird's attempts to make a practical by, I had to rely on comparing the hand-written wide-band transmitter hardware that videodisc player in the late twenties3 video content with knowledge of the messaS,e forced the BBC into using an existing and were encouraged by articles development of 30-line television in Large solution. describing how to do it.a order to determine whether they were "Woman. Head". This The 30-line video signal was low Recently, Jon Weller, a collector of authentic or recent. unflattering enough in bandwidth to be transmitted old electronics equipment, retrieved a meqsage on an existing BBC medium wave fie- collection of direct-cut aluminium The evidence describes the quency normally used for audio. The discs from a house clearance. The Once restoration started, the clues main disc of Betty public simply used their existing radio discs were previously owned and began to appear. In the collection, there Bolton's BBC tv for the audio channel and a second possibly recorded by Marcus Games, are eleven separate recordings of 30- pertormance in radio receiver for the video channel. a keen amateur movie enthusiast. Jon line video. Each recording is a frag- the thirties. Only the display had to be bought - or later discovered that several discs in ment from a programme and lasts no in some cases built. that collection had unusual material more than a minute. There were two Baird's mature 3O-line system - on them, Fig. 3.5 types of programme - one type featur- developed in the late twenties - pro- ing four individual singers and the vided the BBC with an exceptionally What are the recordings of? other containing what may be material low-cost engineering solution that Although the discs were recorded at from children' s programmes. February 1999 ELECTRONICS WORLD 161 HISTORY Sconning options Thc digitalll,' l'cstored irnrgcs lrorn thc sct ol discs do not show thc distor- Two main types of nrechanical scannin14 were usecl ior l0-line (anler.ls ancl clisplavs: tion causecl hl arc-scanning. Thr. onlv Nipkow disc and mirror-drunt. Tl.re Nipkorv ciisc a spiral ring oi.rlrerturcs areupcl the altcrnative cantert \\,as onc hascd on a outer eclge of the disc - createci a curvecl inrage that was sranncrl in an arc. The nrirror nr i rror-dru rn. drum, shown in Fig.4, however scannecl in straight lincs u,ith a slight 'lrorv-lir,'rlistgrti9p. Mirnrr-drurn cuntcras lirr 30-lincs The BBC transmittec.l its images fronr a nrirror clrur-r c.rnrer.r systenr, yet lrrost viervers had a lixccl vcrtical ficlcl-o1'-r,ieu,' ol' rx'cr 20". excludinr blankirrg. used receiver-clisplays basecl on the Nipkow-clisc. They n,ere cheal;r,r.rncl easier lo r-p.rke. .just Hence thc sin-uers who we see in medi- Viewers accepted the ntinor clistortion jr-rst as toclay they sr,rrltrisirrr.rly accept a rr6rptal urr shot werc around 9- l0 t'cct. i.c.2.1- television picture stretchecl to fit a wicle-screen rlisltlay. 3nr. lhrnt the canrcra. With thc bottorn ol'thc blck u,all of the studio in shot. thc irnages shou,that the studio r,r,as largc and thc' callcra \) stcnl u il\ scnrilir c. Shori int e rrrlcrlr teatures colnrnon with thc l9-13 '[-ookin-!r In' rccorclin-u. the quality of carncra-u,ork appcars superior. itrply- ins a latcr date. Relative to \\,hat antatcurs todav achiel'c6 and relativc- to a -senuine -10- linc re-nrake ol'a I 9-10 play7. the inher- ent quality of the vision signrl is excel- lent. With no dctectablc inrasc- crrors. lltc tttirrttr (lrunl cunlerir \\it: ir plL'ei- sion-built r.nechanism. Lishtins. cant- cra-work and production have all been pcrfectll, nratchecl to the 30-line sys- tcnl. Allowin-s lirr the alntost 'cltctaphonc' rccordrng quality. tlte honte-rccor.dcd cliscs shorv details that hare bccn talkcd about bctitre.s but nor sccn . BBC's first television service Thesc then are undoubtcdlv recordings rradc- titrn thc tirst BBC tclcvision ser- vice of l93l-3-5. Thc clLres above sus- gest the tftrnsrnissions cante from the BBC tv stuclio at Portlancl place hetu'cen 193-l and'15. With thc. l9.j-3 prourantnre. 'Looking In'.') rve now have the total contple- nretrt ol t idco rccordinss ol'broadcast te le vision at least in thc UK belirrc thc f ifiics. Since thcy r.,n,erc discovcred and restored only tn the last tuo ycars suggcsts that nrore ntiltcrial may yct irppeirr. Fig. 4. The mirror-drum camera of the thirties scanned the scene uting u proiiii flyirgipotii- Nipkow camera disc of Baird's video recording experiments of the twenties used more traclitional - bul less efficient - lens-based imaging. Singer without the song. Onlv one of thc singers is easily rccognisable hy her clistinctive l'eatures and hair-stylc - Betty Bolton. Fig. 5 As an accom- Fig. 5. Betty plishecl contralto. she rccorcled ntany Bolton. The photo tlitncc-hlrttl \on!\ in lhe latc l\\cnlic\ on the left and its ancl carly thirties. simulated 3O-line Betu'cen 1929 and 193-5 she per- equivalent show lirrrred well o.n,er a dozen tintes on 30- Betty in 1929. The linc broadcasts includint being the tirst two pictures on ,} perlirrnrer on thc openine nisht ol'the the right have BBC Teler,'ision Sen,icc in August been restored off- I 932. disc. One shows Betty' s pertirrr.nancc exucles prot'cs- the glint off sronalisnr. Herc is a highly accorn- Betty's hair and plished pcrtirrrner.