[time-nuts] Allan Deviation -> continuing saga...

[Didier Juges]

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