[time-nuts] Testing 2 Cesiums & GPS

[John Ackermann N8UR]

Brooke Clarke wrote:

> Something is very wrong with s/n 1013.  But the green lock light is one.
> When I turn off the modulation and open the loop, sweeping the control 
> voltage produces a definite peak.  If the true peak was outside the 
> control voltage range how much frequency error would there be?
>
Hi Brooke --

When Corby Dawson walked me through firing up my 5061A, he had me first 
do a rough check with a frequency counter to look for 5.000 000 MHz 
because if the C field was far enough off you could get a lock on a 
secondary peak (there are seven total, with the two nearest the real 
peak being the strongest) which would result in a frequency error of 
about 0.25Hz .  It looks like your error is much less than that, but it 
might not hurt to double check and make sure you're on the right peak.

By the way -- I've been doing some runs of the 5061A versus Z3801A and 
was quite pleased with the offset I apparently had -- after two days, it 
was statistically flat (a few parts in 10e14).  But then last night I 
redid the rack mount which I'm sure jarred the unit a bit, adjusted the 
loop gain as after several days of run time it had drifted up from the 
nominal 40 to 50, and switched to the long time constant.  I also 
adjusted the trigger point on the counter.  Now, a 12 hour run is 
showing about -1x10e-12.  Not sure which of the changes caused that, but 
it's certainly clear to me now that this is a very touchy business!

I'm now dumping all the plots I generate (using the stable-stats.pl tool 
I mentioned a week or so ago) into http://www.febo.com/time-freq/plots/ 
if you're interested.  Not a lot there now, but I hope to soon be doing 
some simultaneous intercomparisons of the Cs, Rb, and GPSDOs that'll be 
plotted there.

John