[time-nuts] Re: Garmin GPS 25 Module

[paul swed]

Andy
So funny. I had some of these old gps units. Like you they sort of died
over time.
I have to say taking the plastic top off was difficult. Never discovered
what was up.
But I did the same as you. The cheap and cheerful NEO-6.
That was the end of any issue.
Regards
Paul
WB8TSL

On Wed, Feb 9, 2022 at 9:23 AM Andy Talbot <andy.g4jnt at gmail.com> wrote:

> I run a set of microwave beacons on a remote site that transmit data modes
> whose Tx timing is controlled from GPS.   They were installed some 20 years
> ago and used a Garmin GPS25-LVS module to deliver NMA and 1 PPS signals to
> all five individual controllers.
>
> After a power outage that lasted a couple of days, the beacons fired up but
> it was clear, after a couple of days timing was corrupted.  Each beacon has
> slightly different controller firmware, and by monitoring the resulting
> corrupted modulation it could be determined what was wrong.    No PPS
> signal was present - which killed modulation on two of them. NMEA timing
> data was present but the time being reported was out by several seconds,
> rendering the data signal transmitted undecodable by most people.
>
> I went up to the remote site to recover the old hardware and am in the
> process of replacing the timing source using a Ublox NEO-6.   Since all the
> beacons were originally designed based on 4800 baud NMEA, the Ublox was set
> for this for backwards compatibility with the Garmin and the configuration
> saved in NV ram.
>
> Now the query I have.   I had assumed it was a 1024 week rollover that
> killed the Garmin, but on testing teh module when I returned home, after a
> longer than normal initialisation period it DID start outputting the
> correct date and time, with PPS present.   So the initial reboot failed,
> even after a couple of days attempt, but after a power cycle it worked.
>
> I'm puzzled by that behaviour.  Is anyone here familar with the GPS25
> family, dating from the turn of the millennium?
>
> As an aside, a Jupiter TU60 GPS module was also in use on site, delivering
> a GPS locked 10kHz signal.   This I used to lock a 10MHz reference in
> "Probably the Simplest GPSDO Possible"  http://g4jnt.com/SimpleGPSDO.pdf
> That module, which is not a lot newer than the Garmin, did appear to have
> survived the reboot as the resulting frequencies of the beacons were
> spot-on when they returned with their modulation faults.  However, in the
> spirit of doing the job properly, it too is being replaced with a
> Leo-Bodnar mini GPSDO.
> All beacon details at scrbg.org
>
>
> Andy
> www.g4jnt.com
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