[GPS_Standard] GPS standard up and running

[Bert, VE2ZAZ]

Hi Chris,

Thanks for your kind words regarding my project. I am happy to hear that you
are happy with the results. I can see that you have spent time adding
features and improvements you felt would make it even more enjoyable.

One small comment I have is regarding the 5/1 MHz switch you have added. The
only reason why I kept this feature with an on-board jumper as opposed to
controlling it via the PIC micro is that the actual 10MHz signal passes
through the jumper contacts. If you extend these with leads to a toggle
switch, you will definitely distort the pulse shape going into the decade
counter. By how much? You are the best person to confirm! As a bare minimum,
I would keep the leads as short as possible and use a good quality switch.
Maybe some small coax would also improve.

Enjoy!

Bert, VE2ZAZ


----- Original Message -----
From: "Chris Dillon" <c.r.dillon at dsl.pipex.com>
To: <GPS_Standard at mailman.qth.net>
Sent: Friday, June 01, 2007 2:09 PM
Subject: [GPS_Standard] GPS standard up and running


Hi Bert - I've just completed the GPS standard and wanted to thank you
for a great project.

It's taken about 6 months since I bought the board and PIC from you but
at last it is working and in a case. My version uses a Rockwell Jupiter
GPS receiver board with an HP 10811 OCXO. I incorporated Jacques'
(VE2AZX) mods to the PCB and also added a 78L05 regulator to supply the
PIC alone. This fits on the board (with the appropriate tracks cut) just
in front of the main 7805 regulator. Following Jacques I brought out the
1 pps to the front panel, and also added a toggle switch to select  a 1
or 5 MHz output from one of the front BNC sockets.

So that I could read the NMEA strings from the Jupiter GPS - and display
satellite data (using the TAC32 demo software) - I arranged to be able
to switch between the Jupiter and PCB serial outputs before going to the
MAX232 TTL-RS232 converter.

The system has now been running for about 36 hours. I'm using an average
sample size (S) of 64 and voting mode. Initially I set up the OCXO so
that it was running within about +0.01Hz of 10MHz with a control voltage
close to zero (0x01EAB - DAC value 7851). From that start the FLL locked
in about 160 secs. As it warmed up it drifted low towards 10 MHz and now
appears to be stabilising at 0x01FD1 (DAC value 8145).  The average
frequency offset  shown by MonTrol is around the low E-10s with the
accumulated total around 4E-10. Standard deviation is about 1.3E-8.

I've not yet compared this with my rubidium standard but this
performance so far seems pretty good to me for a relatively short warm
up time and small sample size. I'll keep an eye on it and see how it
goes over the next few hours - and perhaps increase the sampling time to
an hour or so to see if it makes any difference.

Thanks again Bert - especially for the PCB, pre-programmed PIC, Montrol
software and manual - you've done a great job!

Kind regards

Chris, G3WCD



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