[time-nuts] Signav GPS timing receivers

Magnus Danielson cfmd at bredband.net
Sat Dec 30 23:52:47 EST 2006

From: Dr Bruce Griffiths <bruce.griffiths at xtra.co.nz>
Subject: Re: [time-nuts] Signav GPS timing receivers
Date: Sun, 31 Dec 2006 15:59:45 +1300
Message-ID: <459727A1.5040100 at xtra.co.nz>


> Has anyone used any of the following signav receivers for timing purposes.
> They claim to actually correct the sawtooth error in hardware.
> http://www.signav.com/index_files/PDF_Files/New_Brochures/SigNav%20TM3-01%20Brochure%20V1.2.pdf
> http://www.signav.com/index_files/PDF_Files/New_Brochures/SigNav%20TM3-02%20Brochure%20V1.2.pdf
> http://www.signav.com/index_files/PDF_Files/New_Brochures/SigNav%20Brochure%20TM3%20Evaluation%20Kit%20V1.1.pdf
> The receiver oscillator is disciplined to "eliminate" sawtooth correction.
> The 2nd has a 10Mhz 1E-8 stability reference frequency output.

Considering the options, I'd say that this is basically a modernized version of
the Allstar/Superstar receivers. Most probably it is the Zarlink GP4020/GP2015
chipset at work. The other posibility (uNav) does not neatly match frequencies
and the GP4020 has two extra divide counters which makes the clock output on
the TM3-02 very easy to acheive. The GP4020 also provides a handy SPI interface
so hooking up an external SPI DAC for EFC is trivial. The GP4020 has a refined
PPS output compared to the old GP2021, but it is an interesting "hack" ontop of
the old core, something which could be used to enhance older receivers if one
wishes. That way the 7 second beating pattern can be avoided. Naturally, that
7 second pattern is very predictable and could be included in negative sawtooth
output if you where going down that route.

The core clock is at 40 MHz in those, so a stepup from 10 MHz is trivial (and
indeed how it is done). Also delivering 10 MHz and 1 kHz outputs should not
meet any interesting issues at all.

It is interesting how they are targeting the M12+/M12M market. Looks like a
sweet deal. If you look down their webpages, they seem to have put alot of
their effort into the backend processing, including Kalman filtering, doppler
processing to dead-reckoning moving vehicles with too few satellites in view
etc. All quite doable on the old receiver cores as such, but takes bigger
footprint in software. Looks quite interesting.

Randy said earlier that he where going to sell them, but they don't seem to
have appeared on their web. What is your asking for one of these? I'd sure
like to run it against some other stuff here.

PS. My newly arrived Symmetricom 56k locked up this evening. There's now
another GPSDO in the house featuring both Rb (a TEMEX Rb) and OCXO (OSA 8666).


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