[time-nuts] Rb vs.Crystal OCXO

Charles Steinmetz csteinmetz at yandex.com
Sun Apr 27 05:59:11 UTC 2014

Bert wrote:

>The thunderbolt is one of the best timing devices but not for 
>frequency, if you want high resolution. Over time it is ok but high 
>resolution short gate  times and you see the frequency changes. They 
>use the OCXO to correct for timing  error

I concur with Tom's comments -- I think you have the diagnosis 
wrong.  Using the OCXO to correct the timing error is a feature of 
the TBolt architecture, and it provides a powerful benefit -- no need 
for "sawtooth" correction.  By optimizing the oscillator disciplining 
parameters and protecting the OCXO from fast temperature changes (see 
my previous posts on metal boxes), you can improve the frequency AND 
timing performance of a TBolt to the point that it doesn't have to 
apologize to any other GPSDO.  Lady Heather is an invaluable aid 
here, and compatibility with LH is a huge advantage in favor of any 
GPSDO.  Indeed, "Make sure it is compatible with LH" should probably 
be Rule #2 for time nuts acquiring GPSDOs.  ("Make sure it uses a 
10811-class OCXO" being Rule #1.)

Again, I don't want to discourage anyone from building DIY 
GPSDOs.  But it seems to me the first thing any aspiring time nut 
needs is a benchmark -- a known reliable standard for frequency and 
timing.  Without one, it will be impossible to quantify (or possibly, 
even to qualify) how well an experimental DIY circuit works.  So it 
makes extremely good sense to first acquire a GPSDO with which the 
time nuts community has had extensive experience, and which is 
compatible with a very powerful diagnostic tool (LH).  Then start 
experimenting.  If you do better (or, at least, well enough to 
satisfy yourself), you can always sell the commercial GPSDO and 
recover your investment.

Best regards,


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