[time-nuts] Novatel Dual frequency GNSS receivers on ebay

Gregory Maxwell gmaxwell at gmail.com
Sat Oct 7 15:17:17 EDT 2017


There is an ebay listing for "Novatel GPS-702-GG with SPAN-CPT Single
Enclosure GNSS/INS Receiver + Cable" with a fairly large number
available.

This is a Novatel OEM628 dual frequency receiver (supports GPS,
Glonass, SBAS, apparently including L1C and L2C), plus a three fiber
ring gyros (with bias performance that blows away any mems gyro I've
ever used) and an 3-axis mems acceletrometer in an aluminum case, plus
a decent dual frequency antenna.  This is a generation-ish old kit.
The industrial casing conspires to make it look somewhat less modern
than it actually is.

The receivers have external clock input (though not plumbed to the
outside of the case) which appears to work though I didn't try much
with it yet. Mine came with 2013-ish firmware but easily upgraded to
current (2016) firmware. There is a windows based firmware update tool
which talks to it over serial and is very straight forward (The
firmware update OEM6631.zip can be found via google).

You can communicate with them over serial in ascii, there is extensive
firmware documentation that goes over every command
https://www.novatel.com/assets/Documents/Manuals/om-20000129.pdf  some
of which are specific to other modules. There is also a separate
manual for the inertial navigation specific features (NovAtel SPAN-CPT
Users manual.pdf)

The external clock should allow you to hang it off a more stable
oscillator which will improve the stability of the GNSS results, and
_I presume_ improve the quality of the PPS output-- the firmware
manual and operating manual are thin on details, and mostly just go
into telling you how to adjust the kalman filter constants for
different clock types.

These also appear to support the novatel 'align' mode where you serial
connect two receivers separated by a short baseline and get really
accurate absolute headings; I'm planning on trying that that but
haven't set it up yet.

Looks like uber (last position was ubers offices in denver) had a
fleet of these things. The couple I got run great, including the IMU,
the antennas obviously spent a long time outside, but work fine. The
cable they come with is weird, but I had no problem chopping one end
off and figuring out the pinout (see bottom).

The novatel OEM6 is well supported by rtklib and I was able to get
post-processed positions very easily.

Seller takes best offers a fair amount below the $649 asking price.
Looks like they may have another 30 or so of them.

May be useful for doing time transfer especially with the clock input.
Just using it to get nice dual band observations to precisely survey
an antenna location for a traditional GPSDO may improve GPSDO
performance by a fair amount.

Here is the signals and wire colors on the cables mine came with.
YMMV, I'd suggest not blindly trusting that colors match on other
units.    These cables don't plumb out many of the signals from the
module (in particular, they don't carrying COM2, which is why I
haven't tried multi-receiver headings yet, since I'd need to figure
out how to talk to it over USB if com1 is in use for that), I'm unsure
if they're wired through the to external connector.

01 white          power return (-)
02 brown          9-18 VDC power input (+)
03 yellow        COM1 RS232 TX
05 pink           COM1 RS232 RX
09 green          COM1 GND
10 black          USB D+
11 purple         USB D-
12 yellow brnstp  USB GND
15 red            ODO SIGA
16 blue           ODO SIGA-inv
29 grey pinkstp   PPS (high resistance? 80 ohm)
30 whitw grnstp   Event1
31 red blustp     signal ground



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