[time-nuts] 9390 GPS RX

Ed Palmer ed_palmer at sasktel.net
Tue May 28 18:10:26 EDT 2013

The frequency offset of 3e-9 is still very high.  Since the 9390 will 
discipline the FRK, the C-field adjustment of the FRK doesn't really 
matter.  Before you open up the FRK again, see if the C-field can change 
the frequency.  If it can, and if the range is similar to the specified 
range, then the C-field is working and there's no point in opening the FRK.

As for your AlDev numbers, in no particular order.....

Have you measured the noise floor of your measurement system?
Check the power supply for hum and noise.
Is the crystal control voltage stable or is it noisy?
A weak Rb lamp might give you a noisy signal, even though it's locked.  
Is the lamp voltage noisy?
Check for a bad cable or some other bad connection.  If possible, use 
only double-shielded cables.

Running down problems like this can drive you crazy.  The levels are so 
low that it could be almost anything from the computer you're running 
Timelab on to your neighbor's wireless phone!

A good OCXO often takes a month or more to stabilize after you pick it 
up in an auction.  Rb standards aren't usually that leisurely about 
settling down but I'd just let it run and see what happens. This might 
be a good time to put it back in the 9390 and see what happens.  Does 
the 9390 have commands that will show you how well the FRK is performing?

You also might have a unit that's working properly but is a little 
noisy.  The specs don't cover something like this.  You're well outside 
the time for 'short term stability' but haven't yet got to the 'aging' 
spec.  If you're using the 5370 by itself, you can't measure the short 
term stability at all.


On 5/28/2013 11:37 AM, Mark C. Stephens wrote:
> Ed and Bob,
> The FRK has settled down to 0.03Hz out after 2 days undisturbed (back in its black box).
> Allan deviation @ 800 seconds is 4.88E-12 which I am not terribly happy about.
> -mark

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