<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<HTML><HEAD>
<META content="text/html; charset=US-ASCII" http-equiv=Content-Type>
<META name=GENERATOR content="MSHTML 8.00.6001.18828"></HEAD>
<BODY style="FONT-FAMILY: Arial; COLOR: #000000; FONT-SIZE: 10pt" id=role_body
bottomMargin=7 leftMargin=7 rightMargin=7 topMargin=7><FONT id=role_document
color=#000000 size=2 face=Arial>
<DIV>There was a post some time ago regarding this issue. </DIV>
<DIV> </DIV>
<DIV>First there were different record standards to start. What we know as
Low Band Mono is 4.5 to 5.4. The emphasis curve was different between the
first RCA and Ampex machines. This was later standardized to the Ampex
method.</DIV>
<DIV> </DIV>
<DIV>Because RCA had an early curve that was non standard, there were for years
a variable position on the Demodulator to allow an operator to correct for
this. Look at all the early Low Band machines and you will see this
position.</DIV>
<DIV> </DIV>
<DIV>Third was Low Band Color. It was used to prevent the moire that was
generated between 3.58 and the FM record frequencies. </DIV>
<DIV> </DIV>
<DIV>All systems used direct record and playback.</DIV>
<DIV> </DIV>
<DIV>Now the tricky part. The monochrome playback was good enough without
any time base correction. It met FCC standards and all the TVs could
handle the time base errors. Color was impossible because of the high
degree of stability required to playback NTSC. Even is you had an H Lock,
it was still not stable enough. </DIV>
<DIV> </DIV>
<DIV>RCA came up with a method. They put a color processor rack in the
system. The signal was routed from the demodulator to this rack.
</DIV>
<DIV> </DIV>
<DIV>The signal went to a burst oscillator that stripped the burst from the tape
signal. This would then generate a 3.58 signal know as signal sub
carrier.</DIV>
<DIV> </DIV>
<DIV>The sub carrier converter chassis would then convert the house reference
sub carrier to 19.8 MHz. It also converted the Tape sub carrier to 19.8
MHz. We now have two signals. One that is unstable and one that is
stable.</DIV>
<DIV> </DIV>
<DIV>These signals were sent to the Chroma Processor chassis. Here the
path was as follows.</DIV>
<DIV> </DIV>
<DIV>First the video is sent through a low pass filter to remove the
chroma. There is another path that is a high pass filter to provide chroma
only. The Chroma is mixed with the reference 19.8 MHZ signal.
Buffered and then mixed with the tape 19.8 MHz signal. And guess what, we
now have stable chroma. The chroma is now added back to the mono signal
and we have full color. BUT it is no longer true NTSC because the 3.58 and
the H sync are not locked. </DIV>
<DIV> </DIV>
<DIV>A little bit more to be done. The burst has to be regenerated.
That was the function of the burst processor chassis.</DIV>
<DIV> </DIV>
<DIV>Lastly, the signal was sent to the output proc amp. It had the final job of
allowing for the adjustments required for proper playback.</DIV>
<DIV> </DIV>
<DIV>I have a complete set of schematics for the TRT-1 that include the color
rack. It is interesting to look at this and realize how well the pioneers
did in their design of the quad. Yes there were competing ways to
accomplish the same thing but it still amazes me that the technology is still
useable today.</DIV>
<DIV> </DIV>
<DIV>Chris Hill</DIV></FONT></BODY></HTML>