On 6/19/2012 4:46 PM, Michael J. Mahon wrote:
I don't think that was the earliest design. The RCA 630TS, the reference design for the first commercial set, used a PLL. Of course, based on pulling a crystal oscillator, as were all color TV sets.
May well be the case. I just clearly remember that there were "ringing" designs and was able to fine one reference on the 'net
http://www.hawestv.com/mtv_color/colrtel_burstBlock.htm --------------------Crystal ringer. To generate the reference subcarrier, most TV receivers use a CW (continuous wave) oscillator. Not Col-R-Tel. Instead, the burst signal, multiplied at Col-R-Tel's burst amplifier, shock excites a 3.58 MHz crystal.
During installation, you tie the converter burst amplifier to the horizontal blanking signal. The orange wire makes this connection. When horizontal blanking occurs, it gates on the burst amplifier. The rest of the time, the burst amplifier remains off. (In the Col-R-Tel burst gate circuit, "off" actually means saturated.) When the burst amplifier gates off, the crystal keeps ringing. In fact, the crystal continues to ring over the entire next line period.
----------------------That page describes a converter of a black and white TV to color, but the same principle was used in a number of inexpensive sets.
(However, I still don't recall one without *two* PLLs--one for horizontal sync (and burst gating) and another for color subcarrier recovery.)
Actually I saw designs where there was no PLL for horizontal sync either. Instead a free-running oscillator was tuned a bit lower than the proper frequency but was tripped early by the sync pulses. Like a pulse from a floppy resetting the Woz machine instead of using a PLL for a data separator as in early expensive disk controllers.
-Alex.