[GPS_Standard] Accuracy

[Bert, VE2ZAZ]

Greetings Ott,

Thank you for sharing your findings regarding the GPS receiver signal. When
we consistently pick up 5 or 6 satellites like I do, we tend to assume that
everything is solid and reliable. This may not be the case... I will
certainly keep an eye on the SNR in the future.

It is also good to hear that your $13 GPS does great. Something to
remember...

I have enjoyed developing this system, though it involved a lot of spare
time and observations. Hearing users confirming the performance is
gratifying. Thank you.

Bert, VE2ZAZ



----- Original Message -----
From: "Ott" <ottf at wbia.net>
To: <GPS_Standard at mailman.qth.net>
Sent: Monday, April 30, 2007 8:01 PM
Subject: [GPS_Standard] Accuracy


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
______________________________________________________________
GPS_Standard mailing list
Home: http://mailman.qth.net/mailman/listinfo/gps_standard
Help: http://mailman.qth.net/mmmain.htm
Post: mailto:GPS_Standard at mailman.qth.net