Movies for TV - Early Television Foundation

megacycles,
COLOR 777
with contributions from each of the three color chan-
nels. Appearing at the output of the band-pass filter is "the mixed-
highs signal." These mixed-high frequencies
are fed to an inte-
grator, which is already receiving signals from the sampler and
from the synchronizing generator. The composite signal which
comes out of a filter is applied to the modulator of the transmitter.
At the receiver, the signal from the second detector also enters
the sampler. It is a composite signal. An electronic commutator
samples the composite signal every 0.0877 microsecond, producing
short pulses. The amplitude of each of these pulses is determined
by the amplitude of the composite wave at that particular instant.
The problem has been to convert these signals into color at
the receiver; however, now that RCA has announced and demonstrated
the color tube this last fence has been overcome. Two
types of tube have been developed, a single-gun, and a three-gun
model. In the three-gun tube more or less conventional scanning
is employed, but in the single gun tube the electron beam in ad-
dition to scanning the screen from left to right also rotates in a
spiral, so that the angular position of the beam as it enters the
mesh in front of the screen determines the color to be illuminated.
The commutator feeds pulses into three separate video ampli-
fiers which in turn control three separate guns in the three-gun
tube. In the case of the one-gun tube mixed signals are fed to
the single gun in the tube and color is introduced by modifying
the path of the beam, as mentioned above.
In each tube the phosphor and internal construction are
similar apart from the number of guns. The screen proper con-
sists of 351,000 dots of red, blue, and green arranged in little
triangles of three colors numbering 117,000. Just in front of this
screen is a mesh with 1 1 7,000 holes in it. The angle at which the
electron beam approaches this mesh screen determines the color
spot which will be activated by the beam since only one spot can
be illuminated at a time by the beam.
Normal black and white receivers will produce monochrome
pictures from this transmission and a black and white signal will
produce black and white pictures on the special color tube, so the