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

[Didier Juges]

Magnus Danielson wrote:
> Look at the AD8561 datasheet first. The 74HC4046 is much slower than the
> AD8561 and the higher output slewrate of the AD8561 is certainly good to keep
> jitter down. The 74HC4046 is worse for that aspect.
>
> What I would rather critize Didiers schematic for is the lack of decoupling
> caps. This is good for many reasons, but it includes keeping the rise and
> fall times up and thus the slewrate up and thus the jitter down.
>
>   
There are decoupling caps everywhere, I kept the schematic simple. Same, 
the counters actual wiring is not depicted, it is straight from the 
Texas Instrument data sheet. I also have a 200 ohm pot across the OCXO 
output to adjust the drive level into the 390 ohm resistor not shown.
> I would measure the actual phase-stability and phase-slope of the IF
> transformer solution with aspect to temperature. You may want to lower its Q
> value to flatten the phase-response. You loose in selectivity but gain in
> phase-stability.
>   
I have planned to do that. The transformer I am using is quite 
temperature stable, and the Q is controlled via the 390 ohm resistor, 
which may or may not be the optimal value from a Q standpoint. It is 
close to the best value from a drive level standpoint, to make sure I do 
not overdrive the comparator. I did not observe a measurable change in 
resonance frequency when blowing a hot air gun at it from a distance, 
even though my measurement method was crude (adjust the drive frequency 
using a SG503 and peak the voltage, use scope to monitor).

I could use the 5370 to measure the phase shift while I blow hot air on 
the circuit (transformer and comparator), or I could make a small hot 
box with a light bulb and a variac, put the OCXO and clock shaper in it 
and use my HP3478B voltmeter and a thermistor to record temperature, and 
plot delay and temperature via the GPIB while I crank the temperature, 
then I could plot delay vs. temperature.

The opportunities to experiment are endless... I will never have time 
for all that, I better retire now :-)
> Cheers,
> Magnus
>
>