[time-nuts] 9390 GPS RX

Mark C. Stephens marks at non-stop.com.au
Wed May 29 06:27:11 EDT 2013

Well, what do you know, I turned it up on its end with the heatsink end on a heatsink and overnight it locked dead on 10Mhz.
Well as far as I can go, 10Mhz exactly, to 10 digits.
HDev=1.78E-12 @ 700 Seconds so it's still a teensy weensy wobbly.
Long term stability is awful. 4.7E-11 @ 1:12 before I gave up on it while I was ahead..
I wonder if the stability is correctable?

Also, I was 'gating' my timer to quickly before so some of the previous the readings have been out by miles.


-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On Behalf Of Ed Palmer
Sent: Wednesday, 29 May 2013 8:10 AM
To: time-nuts at febo.com
Subject: Re: [time-nuts] 9390 GPS RX

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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