[BC] Phasitron...

[Dana Puopolo]

From: RichardBJohnson at comcast.net

>The PLL comprised of a number of "regenerative dividers" that divided down the operating frequency  and the frequency of a quartz crystal to audio-frequency "tones" that were applied to a two-pole motor. If the frequencies were different, the motor would turn and adjust a capacitor to bring them together. Since the motor could not turn fast enough to cancel any AF, the frequency control was distortionless. The motor would turn until the average phase of the two signals was the same, preventing any further rotation.
>
>When the FM band was moved up to 88-108 MHz, Western Electric just added a doubler stage so the scheme was no longer "direct-on-carrier..."

This sounds EXACTLY how the carrier syncronyzer at WLLH in Lawrence, MA
worked. The carrier frequency of the Lowell transmitter was divided down to an
audio tone that was sent to Lawrence by a telco line. In Lawrence, the
transmitter there also had its carrier divided down by the same amount. The
rest of the circuit is as you described for the FM PLL, except in this case
the motor turned a crystal trimmer on the Lawrence transmitter. Once a week
the Office Manager used to stop at the Lawrence transmitter on her way to work
and zero beat the tones using a pair of headphones. She told me that it seldom
had to actually be adjusted. In the mid 1960s the whole thing was replaced
with a pair of CTS Knights Frequency Standards, though the sync equipment was
still in Lawrence when I worked for WLLH ten years later. Racks and racks of
vacuum tubes in that Western Electric brown.

-D