What would cause loss of GPS Sync?

We have been having issues where some of our radios lose gps sync.  The number of tracked radios dropps below 4, which as I understand it you need 4 tracked to sync.  What I don't understand is why these radios would go from 10-12 tracked radios down to under 4?  Some are on cell cites and others are not.  Some that loose sync are right next to others that do not loose sync.  Pucks are installed in the gps slot in the ePMP sectors, but one in particualr is installed outside with clear line of site to the southern sky.  I even oriented that puck with the logo facing upward as someone reccomended previously in these fourms.

Does anyone have any ideas?  It's driving me crazy.  This is also happening to our newly installed ePMP 2000, where it went from 13 tracked down to 3, from snr on the tracked radios of 40-50 down to 10-15.  Why would this happen to one radio but not the other that is on the same side, just feet away?

All chips are updated with the newest firmware. AXN_3.20_8174 and AXN_1.51_2838

Hi Matt,

Sometimes in noisy environment external GPS antennas cannot perform with good quality.

They collect electromagnetic radiation and lose satellites tracked because of this.

They are especially sensitive to FM transmitters.

For these cases we recommend to use internal built-in GPS antenna in ePMP Sync devices.

Thank you.

Why use the external GPS at all then? Why not put everything on internal?

Internal antennas are less gain than the puck, receiver saturation can be reduced using a lower gain antenna, but using a lower gain antenna in some situations can cause a loss of sync. Or if your radio is in a metal case. Both antennas have thier ups and down and neither is perfect for all of the different situations out there. For us, the eternal antenna, or ground based sync is needed from the metal housings on the back of the kp sectors.