[GPS_Standard] Accuracy

[Ott]

Firstly, I would like to thank Bert for developing a product that brings back memories of my youth.  Back then folks would actually gather in front of a TV set just starring at the test pattern.  Today I sit in front of my computer watching cycle-to-cycle frequency accuracy changes!
This wistful passing of time is not without its rewards as I have noticed something I'd like to share: 

If you note that your cycle-to-cycle accuracy seems to change significantly, go to the GPS data and note the SNR of the received signals.  You will probably note that your accuracies will deteriorate if the received SNRs are below 40 dB.  This makes good sense as noise on the signal will translate to jitter on the timing pulse.  I have a less than optimum location on a mountainside which has severe blockage over a 60 degree azimuth for elevations of 30 degrees or less.  The result is some serious reception conditions.  However, a good window will allow lock on 4+ birds at better than 40 dB SNR, resulting in lock accuracies down to the mid e-12 figures.  Based on this finding I would say that antenna/preamp improvements could significantly improve overall system performance.  

For the record, my system consists of Bert's board, an HP 10544A oscillator and an AXIOM GPS board available on eBay for $13 USD.  

Thanks again Bert!

Ott, W4WSR