[time-nuts] Lamp for FRK Rubidium Needed

Bob Camp kb8tq at n1k.org
Tue Aug 12 18:30:08 EDT 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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> 
>> 
> 
>> 
> 
> 
> 
> 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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