APs Losing GPS Sync Capability

We have 9 towers up, all but one on water towers. On our site in Cromwell, OK we have a PMP 100 900 omni at the top of the water tower and a CMM3 inside an enclosure at the bottom. The only other thing plugged in is a PTP 100 5.2 backhaul.

The AP on this site will lose power port syncing capability about once per year, at which point we replace it. It does not sync well through the timing port, perhaps because the backhaul is not the same firmware version (we don’t want to upgrade the 5.2 because that will likely drop the power due to the newer FCC compliance). We have replaced the cable, replaced the ends on the replaced cable, and changed CMM ports. We may have even changed CMMs but I’m not sure about that one.

Any ideas? Dirty power? It’s not exactly a trial and error scenario since it only happens about once per year.

Is the cabling shielded?

No. We have in the past. At one point they had us take our equipment down and move it to another tower four miles away while they were fixing and re-painting the tower. When we moved it back I think we replaced the old cable that was there with the gel-filled stuff we’ve been using lately.

But maybe in the past we have not taken full advantage of the shield? Are you supposed to do anything different when you use shielded cable?

I sent my boss a link to the Packetflux Syncpipe Deluxe. Hopefully that will come in soon and will be a cheap solution.

We have that occasionally as well. 900MHz Canopy gear has a SMD diode right next to the ethernet port on the board that sometimes needs replaced to get sync-over-power working again. I don’t remember the details of the component, but we’ve replaced several on our gear over the years. (150 900mhz APs in the network right now)

For a single AP I’d use the same POE injector cord you use with SMs, and mount a Packetflux SyncPipe Parasitic next to the AP - the Parasitic goes inline between the AP and the POE on the ethernet cable to draw its power, then uses a timing cable from the GPS in the SyncPipe to the timing port on the AP. No CMM needed. (If no other tower sites nearby use the same 900mhz channel you can often get away with just generating sync on the AP, but if there’s any geographic or frequency overlap you want stable sync) Not an efficient approach with multiple APs at one site, but can still be used for a single AP that no longer receives sync over power.


Yeah timing signal is veeerrry finicky. With long runs like that your pulse can get distorted. We prefer to keep the run between the CMM and AP as short as possible. SyncPipe would work too, if it’s close to the AP.

When using shielded cable it is necessary to use at least one shielded end and connect the cable’s shield to it with a drain wire. Often times a little dab of solder along with a crimp. However if the device you’re going into isn’t set up to deal with shielded cables then you’d be well off to run the drain wire to an actual grounding stud.