[time-nuts] Need info: Spectrum Instruments brand GPSDO

Thomas S. Knutsen la3pna at gmail.com
Fri Jul 27 14:39:41 EDT 2018

That looks like a re-packaged Spectrum TM-4M: https://i.imgur.com/VKZtQzr.jpg
With the internal lead battery and routing to different front
connectors removed, it looks quite alike.

If so, they can do either their custum binary protocoll or NMEA. I
have been meaning to suggest for Mark Sims that it would be a
apreciated addition to Lady Heather to add the binary protocoll.
I should have a manual around, if the TM-4 manual can't be found on
the internet.

Den fre. 27. jul. 2018 kl. 20:25 skrev ed breya <eb at telight.com>:
> I recently picked up some old cell base station units, and retrieved two
> of what appear to be this unit, from Spectrum Instruments:
> http://www.spectruminstruments.net/products/custom2/custom2.html
> I have asked them if any info is available, but no response yet. If
> anyone knows anything about this unit, I'd appreciate hearing about it.
> Speaking of redundant references, I can picture two identical units
> operating in the "exact" same environment and GPS view, but redundancy
> is not my purpose here. I have tested both units separately, and they
> seem to work and provide GPS and ref lock indications. I've got them
> both mounted in one chassis, with a common PS (15-24 VDC). The plan is
> to feed them both with the same input from one GPS active antenna, and
> then experiment to see how they behave separately and versus each other.
> I assume I can eventually at least talk to the the Motorola GPS RX
> modules, but I don't know about the rest of the custom GPSDO brains.
> There are two DB-9 RS-232 (probably) ports on each unit - apparently one
> for the GPS, and one for the rest.
> One thing I'm wondering is how much interaction/interference may occur
> between the front-ends. I'll be building a module with DC to feed the
> antenna, a preamp stage to boost the signal a little and split it
> between the RXs, and provision to fool them both into thinking their
> usual antenna DC load is present. The post-split RF path lengths will be
> closely matched. I can add extra isolation if needed, but I'd like to
> see what happens.
> I'd expect that their 1 PPS and 10 MHz should ultimately be in phase. I
> don't know if these units do any kind of sawtooth correction, but I
> guess I'll find out eventually. The 1 PPS signals are not available on
> the panels, but I know they're in there.
> As-are, the GPS modules' internal clocks (19.095 MHz marked on XTLs) are
> independent. Other experiments could involve forcing them to be the same.
> Ed
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With Best regards, Thomas S. Knutsen.

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