Interesting. I wonder what other GPSDO units are out there in the cell systems
which might find their way to the surplus market?
By the way, how do you get Lady Heather to show the plot of signal strength vs
az/el? I tried all sorts of different graphing options and read through
everything I could find with no luck.
Peter
On 5/3/2012 8:02 AM, Mark Sims wrote:
Recently Sam managed to poke and prod a Trimble/Nortel GPSTM (NTGS50AA) enough
to wake it up out of its slumber and be recognized by Lady Heather. The
NTGS50AA is a version of the Thunderbolt done for Nortel. It has some
interesting features (like hot-upgradable firmware, single 24 or 48V power
input, cheaper than a tbolt, etc. It also has a few warts... no TSIP command
documentation being the main one and a few commands are definitely different
than the Tbolt.
The wakeup technique is rather crude and can take a couple of minutes (shout a
particular command into its ear until it wakes up). Trimble's software manages
to get it talking immediately. Duplicating the commands that Trimble sends
does not seem to work. Once it wakes up, it stays awake until you power cycle
it or run Trimble's software.
I purchased one of these units from an Ebay seller in Old Cathay (around $70 or
make offer plus $30 shipping) to see what it would take to add support to Lady
Heather. My unit came in a week or so later. I hacked a 48V power connection
(literally) onto the board and powered it up with a wall wart. After some
futzing and puzzling over the proper ribbon cable orientation between the main
board and front panel board, I got the unit woken up using Sam's technique and
puzzled out the commands to make the oscillator disciplining (time constant,
damping, dac gain, etc) work. The old survey location was in a sketchy
Guatemalan smuggler's haven border town at what looks like a private residence.
After running it a while, it became apparent that it works better than the
Thunderbolt. The temperature sensor does not have those glitches that plague
the tbolt. The receiver has a bit more sensitivity. And, best of all, the
oscillator is pretty much immune to external temperature changes (the Tbolt
oscillator makes a good thermometer). The reported OSC and PPS rms errors are
exceedingly low... you have to actively thermally stabilize the Tbolt to
approach these numbers. Hopefully this quality extends to its phase noise, etc
spec. It would be interesting to see what thermally stabilizing the unit would
do...
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