[time-nuts] Lamp for FRK Rubidium Needed
peter at g0rsq.co.uk
Tue Aug 12 15:45:17 EDT 2014
<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
> 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"
> > Thanks
> > Peter
> > G0RSQ
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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
The manual is confusing, as sometimes it talks about a swing of +/- 20 Hz,
and other times +/- 1Hz...
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
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
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?
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
Thanks for the help and comments
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