[time-nuts] New Time nut FRK-H repair questions --- IT Works!!

David Forbes dforbes at dakotacom.net
Fri Nov 23 17:27:07 UTC 2007


At 3:02 PM +1100 11/23/07, swingbyte wrote:
>Thanks for the help - the manual is great.
>I have trimmed the xtal so the control voltage is around 8.5V.  The lock
>output is working - drops from 1.5V to 0.03 volts when locked.
>I only have an old HP5340A with OCXO option as my frequency meter.  It
>reads 10.000000MHz as the output from the FRK.  One thing interesting is
>that before I adjusted the trimmer, the FRK came up at 10MHz from
>power-up, now it approaches from 9.999947MHz but still locks at
>10.000000MHz.   Of course now I have to find a way of calibrating it or
>its going to annoy me like an itch you cant scratch.  I have a GPS
>receiver I have to get going that has a 1PPS output on it.  What would
>be an appropriate way to use this to calibrate the FRK - in my lifetime:)
>Also, my FRK as an option for external frequency control.  I couldn't
>find info in the manual on this ( admit I haven't read it fully yet),
>can anyone tell me how these connectors should be used?
>Thanks for your help.
>
>Tim
>Always wanted my own atomic clock


Tim,

Hi. I recently put an Ebay FRS-N in a box with a nixie clock so that 
I could have a nice little house standard.

The solution I used to set the frequency was to build a 1PPS 
generator based on the one Tom Van Baak designed several years ago. 
Her's the source code; there's a web page associated with it that 
google is not finding for me.
http://www.leapsecond.com/tools/PPSDIV.ASM

I calibrated my clock to GPS by going to a telescope with a GPS 1PPS 
signal form a Datum GPS receiver. The telescope also had an SR620 
time interval counter on hand, which made the job quite easy.

Without the time interval counter, you would have to find some other 
way to compare the 1PPS rising edges. Or build your own time interval 
counter. I realize that's yet another project, but it could be fun.

The frequency accuracy of the FRK is not much better than 10E-10 over 
a year, so that's a reasonable accuracy to adjust it to.

Alternatively you could hook up a very slow PLL to the EFC input to 
keep it locked, assuming that your GPS signal is reliable. There are 
designs for such PLLS, for example Brooks Shera's, on the web. Of 
course, the PLL is a time interval counter in addition to a servo 
loop, so you'd be building a time interval counter anyways.

Have fun!
-- 

--David Forbes, Tucson, AZ
http://www.cathodecorner.com/




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