[time-nuts] Novatel Dual frequency GNSS receivers on ebay
J. L. Trantham
jltran at att.net
Sat Oct 7 17:36:37 EDT 2017
Any idea what they are selling for at this time?
I see that some sold for the BIN price of $349.99 up until June 20. After that, 'Offer Accepted' occurred up through October 5, with a BIN price now of $649.99, all plus $40 shipping.
From: time-nuts [mailto:time-nuts-bounces at febo.com] On Behalf Of Gregory Maxwell
Sent: Saturday, October 07, 2017 2:17 PM
To: Discussion of precise time and frequency measurement
Subject: [time-nuts] Novatel Dual frequency GNSS receivers on ebay
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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