In the quest to check the stability of my OCXOs and make a GPS disciplined oscillator, here is my current progress:
Using parts I had on hand and a couple of free AD8561 samples, I made a synchronous divider for the 10 MHz OCXO to get it closer to 1 Hz. Since I only had two synchronous binary dividers (74F161), I used 7 stages for a ratio of 128, which gives me 78.125 kHz. That is the lowest whole frequency (in Hz) I can get with straight binary counters. The F series is old and thirsty, but fast (120 MHz for these counters). I should be able to run that against the 1 PPS from the GPS, and I will post results when available, I hope sometime during the week end. The clock shaper uses a commercial 10.7 MHz IF transformer, readjusted down to 10 MHz (see schematic at http://www.ko4bb.com/ham_radio/Manuals/2_GPS_Stuff/Clock_Shaper.jpg). It provides light loading to the OCXO through the 390 ohm resistor, yet provides about 2V p-p to the comparator, to get it out of the noise. I do not know the temperature stability of the transformer, or the loaded Q, I will check that later. I realize this is probably not an optimum design, but it's what I could do with what I have on hand. I am not using the fine tooth comb and tweezers yet, I am still with the rake and the fork lift :-) Didier KO4BB _______________________________________________ time-nuts mailing list [email protected] https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
