Recruitment speciol r turn to bock pqges ELECTR NICS Austrio Asch.68.(X) Denmqrk DKr 69.fi) Germony DXI t8.q, Gree Dro.l3(X).(X) Hollond Dfl. I2.5O lioly t.gqX).q) molro Lm. I.65 tR €3.30 Singopore 5$7.50 Spoin Pts. 9(X) RLD usA s6.sO INCORPORATING W!REIESS WORTD A REED BUSINESS PUBI.ICATION SOR DISTRIBUTION SEPTE'YIBER I 998 D2.45 Down of Iv: exclusive pirtures Antennqs from (o-ox Josler roules lo Inlernel Wow qnd flutter melel Proterting rirruitry lUlotor speed (ontroller CAD reuiews WinBoqrd New displqy Ierhnology low power rodio offer - soue t200 llll[Illlltilillillffil hoc mrrnogd io look ot nclevision r€cordod on disc seveniy yeoru cgo - thitry yeors be#orr video nope reconding become Down of possible. Whot is more, rhis is the first time it hos been seen since it lelevision wos recorded. hirty years before videotape Fig, l, Resembling recording, between 1927 and contemporary audio 1928. John Logie Baird experi- discs, these are the mented with recording his television different types of discs signal onto discs. Five years later, that contain the enthusiasts made a few off-air disc worl{s earliest-known recordings of the BBC's 30-line tv recordings of broadcasts. The discs have remained as television. curiosities since then, defuing attempts to retrieve recognisable pictures. For many years I have been seeking out and restoring these discs using soft- ware signal and image processing. The filming a television display - was the images recovered from the discs give a only method of capturing the fleeting remarkable insight into those pioneer- images. Broadcast companies used the ing days of tv. As a bonus, analysing technique widely and for many years the recorded signal and its distortions after the intoduction ofvideotape. The unfolds a wealth of new information quality, however, was always poorer on the mechanical tv era. than the original material largely because it had the extra distortion Recorded live... incurred by being displayed and In television's short history, the filmed. development of video recording tech- nology has lagged behind broadcast The first recordings? television by decades. In 1956, Ampex The earliest direct video recordings in the USA demonstrated and market- appear to come from Ampex's video ed the world's first practical broadcast recorder between 195l-56, or the video recorder. I It was one of the great technological achievements of the tele- vision age and transformed broadcast Fig. 2. A single spiral 30-line Nipkow television services, rapidly becoming lens disc set up for the Baird essential to programme production. standard, The area for imaging or Before videotape,'tele-recording' - display is shown in green, For a l,5m diameter disc, this area is only about *Donold F Mcleon BSc {Hons) CEng FIEE 6cm horizontal by 14cm vertical. September 1998 ELECTRONICS WORLD 745 HISTORY BBC's VERA and RCA's 19532 to support live television. experimental linear video recorders. Recently, I restored several direct In the UK, the earliest tele-record- video recordings, Fig. 1, rhat pre-dare ings come from just after the Second that period. They span the pioneering World War. In the USA, the earliest days from soon after the world's first recording appears to be of 48-line demonstration of television by John mechanical television made in 1930 Logie Baird in 1926 to rhe BBC 30- by GE of Schenectady, New York. line Television Service that ended in Ol the BBC's historic pre-war 405- 1935. They are now recognised as line service that started in 1936, bein_e the earliest video recordings in there is no recorded material other the world. than newsreel and film inserts used How could such recordings have Fig. 4. lohn Logie Baird in 1927 at the Leeds demonstration to the BA. He is posing with a wax cylinder video record/playback system - the Fig. 3. The Baird precursor to standard called for a 'Phonovision'. vertical letter-box The drive shaft format designed for probably viewing people from connected the head-and shoulders Nipkow camera to long-shot. The disc with the subjects that came cylinder drive. across best were No cylinder Fig, 5. This frame-seguential colour those that showed recordings have lSJine dithered image from normal plenty of movement. survived. audio cassette tape was generated by The characteristic the author to simulate what Baird curved picture may have seen in his studio in 1928, comes from using a Nipkow disc. Fig. 5. The author's modelling of Baird's Phonovision recording studio of 1927/28 shows the drive-shaft from the scanning disc connected through a 3:1 worm gear to the record platter. 746 ELECTRONICS WORLD September 1998 H!STORY been made decades before Ampex's achievement? To answer this, we need Fig. 7. Baird's patent for the to review television's roots. 'Phonovisor'. A Nipkow disc under the record platter The dawn of television provides what must be the Spurred on by the discovery of the light cheapest and simplest video sensitivity of selenium in 1873, the replay device ever designed. transmission and reception of still pic- The Phonovisor required the tures over cable was demonstrated in specially prepared the late l9ttr century without the advan- Phonovision discs to be tage of electronics. Fleming's thermion- rccorded synchronously with ic diode valve in 1904 and de Forest's the camera disc. Looking into triode valve and amplifier of l9l2 the viewport, the picture kicked off the electronic revolution that would be seen pertecily was essential for television. By the stable, independent of early twenties, news-picture'facsimi- playback speed. les', some even using digital coding,3 spanned thousands of miles. In contrast to these slow, yet high quality transmissions, television required several pictures per second to give the perception of motion. The advantages offered by electron tubes for television camera and display were recognised (19084, l9l ls) well before their practicality. The practical electron tube display first appeared in the twen- ties and the camera - a major techno- logical challenge in itself- in the thir- ties. Several mostly independent pioneers around the world, including Baird in the UK and Jenkins in the USA, focused on the achievement of a prac- tical television system by adapting what already existed to their purpose. They used the only method of scanning the scene available - mechanical scanning. Of the many methods developed for scanning. the Nipkow disc6 became the Fig. 8. The experimental'Phonovisor' replay device used a large diameter Nipkow most popular. It supported the devel- disc underneath the record platter, A light source at the right shines up through opment of several of the first practical the disc via a mirror. This arrangement could also have been used for recording. television systems for almost half a century after its patent. standard of 1929-1935 was 30 lines per lnventions The Nipkow disc was normally one frame refreshing 12.5 times per second Spurred on financially and technical- spiral of holes or apertures spread Fig. 3. ly by his early demonstrations, from equally around the outer part of a flat Line scanning was vertical, from bot- 1926 to 1928 Baird patented and disc, Fig. 2. The path each aperture tom to top with frame scanning from developed a series of innovations that swept out, through the angle between right to left. Baird chose an aspect ratio Covered almost every engineering apertures, corresponded to a line in the of 3:7 - a vertical letterbox, optimised aspect of television, Fig. 4. image. The radial distance of each suc- for televising individuals from close-up . He demonstrated colour television, cessive aperture changed in equal steps portrait to long-shots. Fig. 5,.stereoscopic television, (near) so that, in one revolution, all the aper- The mechanical nature of his infrared. and long-distance transmission. tures swept out the area of one tv Nipkow-disc-based system, and the In ear,ly 1928, he demonstrated recep- frame. sensitivity and bandwidth of photo- tion of pictures across the Atlantic in By masking off the area and placing a cell-amplifiers, constrained his tele- East Coast USA from transmissions in photocell behind it, we have a televi- vision picture to mere tens of lines Surrey, England. sion camera. By placing a variable light' rather than the hundreds of lines of In the months leading up to that event, source - usually a neon - behind a the electronic systems emerging in the he not only transmitted live images, but similar disc, we have a television dis- thirties. also used his latest experiment, play. With synchronisation of camera However, this low definition turned videodisc recordings.T These and other with display, we have the vision chan- out to offer a distinct advantage. The demonstrations served to establish Baird nel for television. highest vision frequency was so low in the public's eye and to raise general that it was in the audio spectrum. Both awareness of a television revolution. The first demonstration this narrow bandwidth and the ease of Today, littte evidence remains of of television creating different scanning arrange- these early achievements. This makes it First with a demonstration of scanning ments were the main reasons why dilficult to be factual about Baird's con- and display of moving pictures in Baird was able to achieve so many tribution to television - especially in his reflected light was John Logie Baird on 'firsts' - years before they were repeat- most publicised creative era of the late 26th January 1926. Baird's transmitted ed in electronic television. 1920s. September 1998 ELECTRONICS WORLD 747 HISTORY Various interpretations of his works discoveries made.