[GPS_Standard] GPS standard up and running

[Chris Dillon]

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