[time-nuts] Lamp for FRK Rubidium Needed
Bob Camp
kb8tq at n1k.org
Tue Aug 12 22:30:08 UTC 2014
Hi
(see below)
On Aug 12, 2014, at 3:45 PM, Peter Walker <peter at g0rsq.co.uk> wrote:
> <EWKehren at ...> writes:
>
>
>
>>
>
>> Having had more than ten FRK's and M100's on my bench and once locked none
>
>
>> where as low as any thing in E-9. What you should buy is a ubox for $ 16
>
>
>> shipping included and you will with your counter be able to get better
> than
>
>> 1 E-9 for testing.
>
>> Bert Kehren
>
>>
>
>>
>
>> In a message dated 8/10/2014 2:30:50 P.M. Eastern Daylight Time,
>
>> ed_palmer at ... writes:
>
>>
>
>> How did you make the measurement that showed a 0.8 Hz difference? What
>
>> are the specs on your Racal reference? When was it calibrated and
>
>> against what standard? That will tell you how much confidence to put in
>
>> it's frequency.
>
>>
>
>> As others have said, an FRK isn't a primary standard and should be
>
>> calibrated against a primary standard. However, 0.8 Hz is an error of
>
>> 8e-8. I don't believe it's possible for a Rb standard to lock and be
>
>> that far off.
>
>>
>
>
>
>>>
>
>>> Sorry if dumb questions, but just starting my quest for "time nut"
>
>> status!!!
>
>>>
>
>>> Thanks
>
>>>
>
>>> Peter
>
>>> G0RSQ
>
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>
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>
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>
>>
>
>>
>
>
>
> Thanks for the interest in my questions.
>
>
>
> Unfortunately the FRK has now decided to stop locking, so I need to go back
> to fault finding. I suspect the problem is with the "hunting" of the 10Mhz
> ref oscillator, as I get a swing of over 300Hz, which I am sure is far to
> big.
>
> The manual is confusing, as sometimes it talks about a swing of +/- 20 Hz,
> and other times +/- 1Hz…
>
At some points it’s talking about the OC-VCXO range, at other points it’s talking about the tune range when locked using the C field.
>
>
> In answer to the questions:-
>
>
>
> After the FRK locked up, I connected it to my Racal 1998 counter, which has
>
> the external reference coming from a Racal 9480 mainframe, which is running
>
> its back-up internal ovened frequency reference (last calibration was about
>
> 5 years ago before i acquired it!) (it is this that I want to connect the
>
> FRK to as its main frequency source). I had a reading which was 0.8 Hz down
>
> on 10 MHz. I left this for about 1 hour to see if anything changed, but it
>
> did not.
>
> I then connected both oscillators to the input channels of my oscilloscope
>
> (Tek 2465B), triggering of the FRK, and saw a fairly rapid movement on the
>
> ovened waveform. All this indicates to me one of the references is out by
> 0.8Hz.
>
>
>
> I understand that rubidium is not a primary frequency standard and the
>
> output is synthesized, but was hoping that some clever technique was used to
>
> ensure a certain level of reliability. How far off frequency could one be
>
> and still lock?
Normal accuracy even if it’s been off a long time should be < 10 ppb.
If the Cell is off frequency it will lock over a *much* wider range. 10 or 20 ppm is quite possible in this case.
>
>
>
> I do have an old "Off Air" standard frequency receiver (similar to a "quartz
>
> lock") which receives "Droitwich" on 192KHz, which gives a 10MHz output.
>
> However I am unsure how suitable this is for calibrating my FRK. I will give
>
> it a try this week, and see how it compares with the FRK.
>
>
>
> I also have a Trimble (not a thunderbolt) GPSDO bought from a seller in
>
> china, which I am yet to set up and try, so maybe this will be my next
>
> project (but maybe I will be asking the same questions when this is
>
> running!!!!).
>
>
>
> Thanks for the help and comments
>
>
>
> Peter
>
> G0RSQ
>
>
>
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Do you have an antenna for the T-Bolt?
Do you have power for the T-Bolt?
If yes to both, then that’s a simple solution to the problem.
Bob
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