PMP450 MicroPoP out of sync events

Our 5GHz integrated sector MicroPoP experiences frequent “GPS is out of sync” events using the on-board GPS. Is anyone else experiencing this?
I upgraded to 20.2.21 because I see in the release notes that 20.2.2. included a fix for MicroPoP connectorized on board GPS not working. The software upgrade didn’t help.
When sync is active and I check the the AP it typically reports around 20 satellites visible. As I watch the visible satellite information the number of tracked satellites is in the 3 - 5 range (usually 4). The AP is mounted on a wall that faces mostly east and a little south. I haven’t observed the sync problem occurring while I watch the satellite info. Is this just a case of the on-board GPS not seeing enough satellites or is it possible that something more is going on?

Hi Don,

is your MicroPoP sector AP still experiencing frequent out of sync events? If so, would you be able to collect an engineering.cgi log after you see a recent sync loss? Our Development team can analyze the log to try to understand what is causing these losses. Ideally the log should be collected within an hour following a sync loss event.

The number of visible satellites you reported seems fairly typical, but your tracked satellite count is very low. As you may know, a minimum of 4 satellites must be tracked to achieve a 3D fix, and 3 satellites are needed for a 2D fix. With the low numbers you are seeing it is not surprising that the AP is not able to maintain stable GPS sync. We generally expect to see the tracked satellite count in the double digit range when the GPS receiver has a good signal and a clear view of the sky.

While we are waiting for the log, it would interesting to see what the AP is reporting about the visible and tracked satellites. If you have a screenshot of the GUI Sync Status page that you could send us that would be very helpful. We would be able to check the measured SNR for all of the tracked satellites.

Many thanks,



Hi Dave
Thanks for your reply. As I watched our Sync Status I saw the number of tracked satellites go as high as 6, and then down to 0 when there was no sync. I’ll mail you a cgi file. Here’s screenshot showing 3 satellites being tracked. Lots of satellites with SNR = 0 Maybe the MicroPoP is just not installed in a good location.

Hi Don,

thanks for sending the files. I believe that the GUI displays an SNR of zero when the signal quality is not sufficient for the GPS receiver to make an accurate measurement. It is common to see zero reported for some of the visible satellites even when the AP is mounted in a good location.

What jumps out at me from the screenshot is that your AP is not tracking any GPS satellites, and is only able to track a few GLONASS satellites. In the North America region we generally see a mix of GPS, GLONASS and Galileo satellites being tracked, with the majority being GPS. The GLONASS satellites alone may not be enough to provide a stable 3D fix. I notice that you do not have Galileo enabled on your AP; you can change this under the Sync Setting section of the General Configuration page, and it may help prevent the sync losses until we can resolve the GPS problem.

Was this AP installed recently, and has it been experiencing sync loss since it was first powered on, or was it operational for some time before this started happening? Also is the sync loss occuring essentially constantly, or have you noticed any pattern to it? For example, does it tend to happen more frequently at certain times of the day?

The first basic thing we would suggest is to try power cycling the unit, if you have the ability to do so. This will restart the GPS receiver and clear the list of satellites. We can then see if the AP is able to lock on to the GPS satellites from a cold start.

The next step would be to check for a local source of interference that could be desensitizing the receiver in the GPS band. Nearby transmitters such as LTE, 5G, 900 MHz band, HDTV, etc. have the potential to interfere with GPS operation. Ideally it would be useful to set up a test AP nearby with a UGPS or cnPulse unit connected to its Aux port, which would confirm if GPS reception is a problem in the general area. However, I know this would likely be very difficult unless you happen to have another AP already installed in the vicinity.

Best regards,


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Thanks Dave
The AP has been experiencing sync loss since it was first installed. We normally have it set to Generate Sync in order to avoid the event notifications.
I checked some other screenshots from yesterday and they also show GLONASS being tracked but not GPS.
I did try enabling all of the satellite types at one point but we still experienced loss of sync events.
I haven’t noticed any pattern in the timing - it seems like we always start to lose sync within an hour or so of enabling Autosync.
We have a nearby tower (500 metres) with PMP450i APs and CMM5 that is able to maintain sync.
I’ll try power cycling and report back. It may be a week or two before I can get to the location.

Thanks Don. Do you happen to have any photos of the installation that you’d be willing to share with us? Ideally something showing the environment that the device is installed in as well as a closer view of the AP mounting itself? This would give us a better idea of what sort of a view of the sky the GPS receiver is getting, and whether there is any other equipment installed nearby that could be a source of interference.

If power cycling does not help and there is no obvious source of GPS band interference nearby, we might need to consider initiating the RMA process for this AP. If you have a spare MicroPoP AP available, it would be worth swapping it in to see if it is also affected or if the problem is specific to the currently installed unit. Alternatively you could try powering up the AP on the ground away from any possible restrictions, if that is a viable option in this location.

Best regards,