THE WAR YEARS
Toward the start of the year Du Mont demonstrate a television incorporating
a monster 20-inch C.R.T (a size that would not be seen in Britain until the
start of the 1950's). The set also featured a "full automatic" timebase,
which (it was claimed) eliminated the need for any horizontal or vertical
hold controls. From the limited technical description, I suspect the scheme
would instead have caused drift in the width and height of the picture, although
this would have been far less objectionable to the viewer than would have
been the effects of timebase oscillators drifting.
In the late thirties and start of the forties, it was left to companies such
as R.C.A., G.E., Philco, DuMont and Zenith to run their own television stations.
Financed from the proceeds of their radio and electronics industries, they
were not profitable but instead were seen as an investment in future technoligies.
From 1st July 1941, the F.C.C. authorised the startof commercial television
using the 525-line standard.
In mid-1940 R.C.A. demonstrated their projection system at a meeting for their stockholders. It utilised a small electromagnetically deflected 4-inch diameter C.R.T. (or "kinescope") operated at 56,000 volts to project a 6-by-4½ foot image.
|The small kinescope removed from the
projection housing, plus 16-inch
mirror still in unit.
|Projection unit on top of power supply
unit, with timbase units in
Also during this period, the 10AP4 C.R.T. entered production. As well as having a flat face, it was possiblt the first television C.R.T. to use a bent gun arangement in conjunction with a correcting magnet (an "Ion Trap") in order to avoid ions hitting teh ecreen material. If ions hit teh screen material then over time this would lead to ion burn, an effect which appeared as a defocussed dark circle burnt into teh screen phosphor.
The German 441-line system, introduced in 1937, remained in effect in Berlin until 1943 when the television tower was destroyed in an air raid. Even more surprising is the fact that the Germans took their television system to occupied France. From 1942 until their retreat in 1944, the Germans broadcast live cabarets as well as newsreels and short films from their captured transmitter on the Eiffel Tower. Both the Berlin and Paris transmitters were almost exclusively used to televise programs for wounded soldiers, with around 500 French-made television sets and about a 100 German sets in Parisian hospitals.
For two years these broadcasts were monitored by the R.A.F. intelligence
service. A television receiving station was set up at Beachy Head to intercept
transmissions from Paris, for which Wing Cdr. G.T.Kelsey secured two televisions
from E.M.I. (a company for which he would later become an employee). The aerial
consisted of a curtain array of 32 dipoles slung between two 150ft masts ;
this was found necessary to eliminate strong signals from nearby radar stations.
The transmisisons often contained news reels of bomb damage to France which
provided useful information for the R.A.F.
France was quick to resume television transmissions after the war, re-opening on the 1st October 1945 using the same 455-line system that they had uesed before the war..
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19th August 2007