[time-nuts] Lamp for FRK Rubidium Needed

Peter Walker 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" 

> status!!!

> >

> >  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

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


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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