[time-nuts] NTP Clock suggestions?

Al Wolfe alw.k9si at gmail.com
Tue May 28 20:04:32 EDT 2013


     I actually built a contraption like this back in the 1970's. As chief 
engineer at a couple of automated radio stations, I was tasked with keeping 
the network-joiner clocks accurate. It sounded really sloppy to have dead 
air or to up-cut the network. These clocks were 60 htz synchronous motors 
that ran cam switches. Real PITA to adjust. Unfortunately, the utility power 
drifted up and down frequency wise, a few seconds a week. Long term was 
pretty good, though.

    I built a 10 mhz crystal oscillator and divided it down to 50 htz. with 
a string of 7490 decade dividers. Then built a 600 htz VCO out of a pair of 
7400 NAND gates biased linearly. Divided the 600 by 12 with a 7492 and PLLed 
the 50 htz results with the precision 50 htz to control the 600 htz. Then 
divided the 600 by 10 in another 7490 to get 60 htz. Low passed this 60 htz 
square wave so it kind of looked like a sine wave and drove a small PA 
amplifier (pair of 6L6's I think.) This drove a 6.3 V filament transformer 
backwards to supply the 120 VAC to power the synchronous clock motors as 
well as some wall clocks.

    A kluge but it worked great. Every one was happy, the owner, the GM, the 
PD, and me because they got off my back about sloppy timing with the net 
joiner. About once a month or so I would fire up the old SP600 in the rack 
and check zero beat  of the 10 mhz timebase against WWV with Lissijous 
figures on an oscilloscope. (Used the VFO of the SP600 do drive a cathode 
follower into a mixer so the the scope was looking at the low IF frequency. 
Zero beat was very obvious and the stability of the receive was not an 
issue.)

    This thing ran fine for at least ten years. The stations changed formats 
so they didn't need it any more. Probably wound up in a dumpster.

Al,  retired  (A.K.A. K9SI)



> albertson.chris at gmail.com said:
>> OK, the LOWEST cost option I can think of for driving an analog clock 
>> with
>> millisecond accuracy.   Buy a normal AC powered clock that uses a
>> synchronous AC motor that runs off the 60Hz AC power, not a battery 
>> powered
>> clock.  Then have your NTP disciplined computer generate a 60Hz audio 
>> sine
>> wave.  Amplify the sine wave to 12 volts then use a small 12:120 volt
>> transformer to step up to 120VAC.  ...



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