[time-nuts] Need info: Spectrum Instruments brand GPSDO
eb at telight.com
Fri Jul 27 14:24:35 EDT 2018
I recently picked up some old cell base station units, and retrieved two
of what appear to be this unit, from Spectrum Instruments:
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.
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