GPS Problem

Please help,

I have lost the GPS sync on my CMM. I have worked around the problem with sync cables connected to timing port, but that is not stable, I’m loosing GPS Sync Pulse often and we are having trouble working on cold weather.

Besides the possible solution for the GPS antenna can anybody help me how to connect the one access point to timing port on the CMM? The idea is one AP to generate the sync pulse, GPS Timing Pulse on the CMM to be set as slave, and other AP to receive the Sync Pulse trough the power port. How should I make the cable if it is possible?

Below is the situation with the CMM

Device type
CMM 0a-00-3e-e0-01-9d
Software Version
CANOPY CMM 2.1.1 Aug 12 2004 10:54:59
System Time

02:13:14pm Thu Dec 09 2004

Up Time
Satellites Visible
Satellites Tracked
N41 58.6130
E21 24.4340
642 meters
Tracking Mode
Acquiring Satellites

SYNC Pulse Status

Have you tested the LMR cable between the antenna and the GPS receiver? There is an article on the knowledge base that shows expected values and how to do so: … d=247&c=14

If all levels are as expected then I would look at possibly moving your antenna to a different location.

I had the same problem. Figured it was a raven sitting on the GPS antenna for a bit (CMM ison the roof of the prep plant at a coal mine). Turned out to be the LMR-400 cable between the CMM and the GPS antenna. At the time I didn’t want to play around so I replaced the entire CMM, with GPS antenna, and cable. I later found the intermittent cable in the shop during testing.

That said, with the new CMM in place, the GPS stats on my AP and BHM both read all zeros. The tracking mode says “Reserved” instead of 3D Track. They act as though I am passing timing from a slave to a master but I’m not. Any ideas on this? Anybody? Everything seems to work fine though so I’m not too excited about it (it’s been that way for about 2 months now).



Are you using a CMM2 or a CMM3 (CMM Micro)?

We are using the CMM2 in a couple of places. The next few jobs we will be doing will have CMM micros.


I’ll toss out some experience here. This happened almost a year ago, so some details have been lost in the fog of my memory.

We had a CMM2 that, for some unknown reason, would drop GPS sync after about 10 minutes of operation. GPS status would show with some error, and receiver information was basically garbage.

Calls into Canopy Tech Support were basically worthless, I talked to several script kiddies who were obviously reading off a list of questions, not someone who actually knew something about the product. The general gist, ultimately, was that the whole CMM2 would have to be pulled out and sent back for warranty repair. Yeah, take my whole canopy network down so the CMM could be sent back, they wouldn’t even send a replacement to run on in the interim.

Did some digging into the chassis and realized that the GPS module was a Motorola (of course) Oncore M12+ Timing GPS receiver. Aha, I just so happen to have one of those lying around on my workbench (I’m also a Ham Operator doing stuff with APRS). Only difference between the receiver I had and the one in the CMM2 was that mine didn’t have the backup battery onboard.

So, I powered down the chassis and swapped out GPS modules. Brought the thing back up, and it has been running wonderfully ever since.

Called back into tech support again and explained what I found, and just asked them to send me a replacement GPS module. Hah, no way, it has to be a whole unit replacement, they couldn’t swap any parts at all.

Finally, I just said to hell with it. Being out the $80 for the spare GPS module I had, cost far less than the frustration I was going to have to deal with in getting the CMM2 replaced.

GPS Receiver info from a normal CMM2 shows:
SFTW P/N # 61-G10268A
MODEL # P283T12T11
HWDR P/N # 2
SERIAL # <yeah right>

GPS Receiver info from the CMM2 in which I replaced the Oncore:
SFTW P/N # 61-G10268A
MODEL # P273T12T11
HWDR P/N # 2
SERIAL # <yeah right>

Having said all this, if you have GPS problems and it’s not the cable or antenna, may be worth swapping out the GPS Receiver module itself. I’ll make a shameless plug, has the Oncore M12+ modules.


Edit: Corrected GPS Part Description

Thanks for the info on the receiver.

It doesn’t surprise me that they wanted the entire CMM back. Otherwise they can’t prove that the GPS receiver was the only problem. The are not allowed to believe that any of us have any technical knowledge and exeperience and can do the same tests they do. The only difference between them and us is they have all of the schematics and service manuals. And more throw-away parts.

I like the

script kiddies who were obviously reading off a list of questions
. :smiley: How true is that?!! :lol:


Interestingly enough, the GPS board provides a 1PPS as well as +3VDC and -3VDC TTL signalling out. If you ever read the pinout of the RJ25 port on a radio, pin 1 is 1PPS, pins 2 and 3 are +3/-3VDC TTL. Gee, where do you think those go??? :wink:

I have been playing with in my spare time, which has been very rare lately, creating an arrangement to distribute the 1PPS and +3/-3 TTL signals to a bunch of ports, obviously for distribution to radio units. The 1PPS can be done in a pure buss-bar arrangement, I’m still looking at what is necessary for the TTL bus, if I have to use something like a 1488/1489 to keep the signal levels up. More difficult is developing the power to feed to the GPS module… it wants a regulated +3.0VDC to power the module itself, and +5VDC on a pin which feeds out to the GPS antenna. A 7805 does the job nicely for producing the +5VDC for the antenna when using a standard +13.8VDC power supply. I’ve yet to come up with a good conversion from either +13.8 or +5 down to the regulated +3.0 that the GPS board wants.

Now if only Canopy would support 802.3af for inline power… <wishful thinking>

For those who are reading this thread and haven’t looked into the 802.1q thread in the suggestions discussion, here’s why I’m doing this. If I can come up with an extremely low-cost CMM equivalent which provides ONLY the 1PPS and TTL information, then I can use whatever back-end network switches I desire, like those that can support 802.1q VLAN tagging, since CMM2 and CMM3 can’t do it.

I am having GPS sync issue here with a CMM Micro unit. It show plenty of satelites visible but barely tracks 3-4 and occasionally loses sync entirely. This unit has been in service for about 7 years. Trouble started after a big wind storm that popped the GPS antenna off the mount such that it was just blowing in teh wind. No other damage visible. Placed GPS antenna back on the mount - its eems to work find for about 5-10 minutes and then the number of tracked satellites fell off to <4. Replaced the GPS antenna and had the same results.

I suspect that the GPS timing receiver is the fault - but why after the wind storm is beyond me. The CMM enclosure was not affected by the wind at all. Somehow it seems that the GPS receive in the CMM has was in some way damaged.

I am particularly interested in your postiing about using the Oncore M12+ unit to replace the existing GPS received in teh CMM micro. In reading your posting it seems that it was just a plug-n-play swap for the Oncore M12+. Thank you for the link to the Synergy units. Can you enlighten me if there was anything more involved? 



That strongly implies to me that either the cable or antenna was damaged by the wind but the damage isn't visibly apparent.  Replacing the cable seems warranted.

The GPS antennae aren't perfectly sealed along the screw holes on the bottom so it's also possible that water got into it when it wasn't level.  You can see that by comparing the resistence of a known good antenna against the one that is giving you a hard time.