[time-nuts] Lamp for FRK Rubidium Needed

Bob Camp kb8tq at n1k.org
Sun Aug 10 13:06:38 UTC 2014


Hi

Simple answer - you need something to compare it to.

Longer answer - Rubidium is a secondary frequency standard. A variety of things can pull it off frequency. One of the issues in FRK style Rb production is the number of lamps that get made to far off frequency to be useful. 

Easy solutions:

1) Beg / borrow / steal a GPSDO for a week or two.
2) Divide down and compare against WWV time ticks for about 12 days per observation. 
3) Visit a friend with a working Cesium standard. 
4) Get a $17 eBay GPS and compare for a week or so. 

Yes there are many other possible approaches. Some of the above assumes you have a fairly good dual channel scope. 

Math on the WWV time tick:

There are a bit over a million seconds in 12 days (1036800). If you measure to one second, you get a ppm. If you can resolve to 1 ms (~1/2 cycle on the tick) you are at 1 ppb. Your Rb should warm up for at least a week before you tweak it. You should confirm any adjustment for at least a week after you do it. A 12 day measurement process isn’t all that crazy in this case. 

Bob

On Aug 10, 2014, at 6:01 AM, Peter <peter at g0rsq.co.uk> wrote:

> Chuck Harris <cfharris at ...> writes:
> 
>> 
>> Paul's description is spot on.
>> 
> 
>> 
>> Once the bulb is clear, you are done.  The real truth is
>> once it is clearer than it was, it is going to work better
>> than it did... When it is all the way clear, it is a good
>> as it was when it was new, and  should last as long as a
>> new bulb would have.
>> 
>> -Chuck Harris
>> 
>> Peter wrote:
>>> 
>>> 
>>> paul swed <paulswedb <at> ...> writes:
>>> 
>>>> 
>>>> Chuck is correct I have done this trick on FRS units. The glass clears and
>>>> the lamp re-ignites and continues to work for a long time. Actually it
>>>> hasn't failed and this must be 2 years now.
>>>> Regards
>>>> Paul
>>>> WB8TSL
>>>> 
>> 
> 
> Thanks to the help from members here I now have a locking FRK.
> 
> My bulb looked pretty clear, and i couldnt find any deposits or "bits"
> inside, but decided to give it a good soaking at about 150 deg C using my
> hot air re-work gun for about 10 mins.
> 
> I have checked it against my Racal ovened reference and found a discrepancy
> of about 0.8 Hz.
> 
> Now the million dollar question...Can I be sure the FRK is good before I
> start to use it as my standard frequency?
> 
> Is the FRK constructed in such a way that the frequency accuracy is assured,
> or do I need some way of verifying the FRK, or calibrating it.
> 
> I dont want to trim my ovened reference to the rubidium, only to find the
> rubidium is not as accurate as I thought?
> 
> Sorry if dumb questions, but just starting my quest for "time nut" status!!!
> 
> Thanks
> 
> Peter
> G0RSQ
> 
> 
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