[time-nuts] FE-5680 frequency jump

[Volker Esper]

Thank you for this information, Bob! I have to reconsider the frequency 
jumps of my GPSDOs...
Volker

Am 05.04.2013 20:59, schrieb Bob Quenelle:
> I found the cause of the 4 mHz  frequency jump.  I have an LPRO-101, 
> an FE-5680, power supplies and a Motorola M12T GPS board in a surplus 
> case. When I put the case away to work on another project I piled the 
> hockey puck antenna and lead in the case and it happened to land on 
> the FE-5680.  I noticed the antenna stuck firmly to the FE-5680 case 
> when I got the project back out.  I found I could get a 6 mHz (0.6 
> ppb) shift comparing the frequency with residual magnetism from the 
> magnet stuck on the FE-5680 case to the frequency after demagnetizing 
> the FE-5680 case.  Unintentional C field adjustment.  Dope slap, live 
> and learn.
> Bob
>
> -----Original Message----- From: Magnus Danielson
> Sent: Monday, April 01, 2013 5:13 PM
> To: time-nuts at febo.com
> Subject: Re: [time-nuts] FE-5680 frequency jump
>
> On 04/02/2013 01:12 AM, Attila Kinali wrote:
>> On Mon, 01 Apr 2013 23:57:48 +0200
>> Magnus Danielson<magnus at rubidium.dyndns.org>  wrote:
>>
>>> On 04/01/2013 10:06 PM, Bob Quenelle wrote:
>>>> I’ve been running an FE-5680 for maybe a total of 50 hours over the 
>>>> last
>>>> several months.  I found that an offset setting of 180 made it 
>>>> track GPS and
>>>> (previously-set) LPRO-101 10 MHz signals.  Even with power cycling, 
>>>> after
>>>> about 1/2 hour, with an offset setting of 180 the FE-5680 was 
>>>> stable. The
>>>> last time I turned on the FE-5680, it drifted with a setting of 180 
>>>> and
>>>> needed a new setting of –415 to track the other signals.  That’s a 
>>>> change of
>>>> 595 counts and with a resolution of 6.8 uHz per count, a frequency 
>>>> change of
>>>> 4 mHz (0.004 Hz) and 0.4 ppb.   Operation at the new setting is 
>>>> stable for
>>>> now.  The lock signal indicates lock and the power supply voltage 
>>>> is still
>>>> 15V.  I haven’t checked lamp voltage or VCXO voltage as that requires
>>>>   opening the case.
>>>
>>> How long have it been turned on since last power-up?
>>>
>>> Let it sit for a day at least.
>>>
>>> I've found that it is easy to be in too much hurry to judge the
>>> situation and trim things efter power-up. The crystal oscillator just
>>> doesn't get the time to settle in.
>>
>> That might be indeed the case. Figure 3 in [1] gives "quite high"
>> frequency aging differences after switch on and long run time.
>>
>>
>>
>> Attila Kinali
>>
>> [1] 
>> http://www.pi5.uni-stuttgart.de/common/show_file.php/lectures/100/blaetter/The%20Rubidium%20Clock%20and%20Basic%20Research.pdf 
>>
>>
>
> You are confusing the VCXOs frequency drift with that of the rubidiums
> (which is the result of the FLL locking of the VCXO to the rubidium
> "resonance").
>
> If the VCXO still has a fair distance to drift, then false locking can
> occur while compating the initially quite vigorous drift rate. The only
> real way to handle that is to sit and wait for it to settle down. Only
> after that may trimming of the oscillator be done to zeroize the
> integrator state.
>
> A small commercial rubidium doesn't need very long to "get a feel" if it
> is in good condition or not, but sitting on your hands and let it warm
> up gives you a fair idea of just how skewed situation it is. That's also
> true for caesium clocks.
>
> So, sit on your hands and let it settle. Better yet, leave on while you
> do other things. Just recall to put enought cooling on it!
>
> Cheers,
> Magnus
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