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

John Ackermann N8UR jra at febo.com
Sat Oct 28 08:36:43 EDT 2006

Didier Juges said the following on 10/28/2006 12:18 AM:

> 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 :-)

To minimize jitter and tempco, you probably ought to stay away from a
comparator if you can.  I've had good success using the input circuit
from Brooks Shera's GPSDO which is a 74HC4046 PLL, but using only the
input circuit and not the PLL section itself.  Alternatively, you might
get away with a simple capacitor followed by 50/50 voltage divider to
provide 1/2 Vcc bias going to the input of the divider chip.


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