Hi all, running 4.6.1RC27 on a epmp 3000L and I see now there is a handy graph showing the gps satellites and the SNR, what do you think about this…
As per a post by Fedor this is passable but is it really adequate? The radio is not modulating the best.
What do you mean by “the radio is not modulating the best.” Do you mean that the GPS radio is not getting a lock to enough satellites and is losing sync often… OR do you mean that the SM’s attached to this specific AP have poor modulation?
On it’s face, GPS sync and AP/SM modulation don’t have anything to do with each other. That being said, if your losing GPS sync on one or more collocated AP’s that need to have sync in order to support the desired channel plan (e.g. back to back frequency reuse and/or tight or no guard bands on adjacent channel use between AP’s), that might cause one or more AP’s to have modulation issues. Symptoms include poor modulation to all SM’s, many SM’s deregistering frequently all at the same time at semi-regular intervals.
The ePMP GPS hold off timer can help a little bit, but eventually the sync will drift and unless a GPS lock is obtained soon, then sync issues can occur.
Based on the pic I provided what can I do to increase the SNR of the satellites… Install pucks instead of using internal? I have a couple epmp 3000 with external pucks that are tracking over 20 satellites but the SNR is poor.
Here are two epmp 3000 radios, one facing east … has great snr to satellites and the other, west facing, does not…
East facing…
West facing…
Here are the other 2 epmp 3000 on that tower… North facing and south facing…
North Facing…
South Facing…
It would be very interesting to see your West facing 3000 (only 4 yellow sat signals) and with no changes, other than connecting an external GPS puck, and positioning the puck so it’s clear to the southern sky.
I think if you contact Cambium Support via a Support Ticket, they may send you some of the latest/greatest pucks (I’m not sure what the policy is) but that AP would be a great test I think.
Those 4 pics are epmp 3000 all with pucks… top of tower with no obstructions to sky. I am wondering if the west one is possibly disrupting the sync… these 4 are using frequency reuse with their respected partner.
Well the West one certainly has some issue with receiving Satellite GPS signals. So, either the GPS puck is broken, or the GPS puck is mounted where it’s blocked, or there’s a connector loose or broken or something. It’s obviously not getting anywhere near enough GPS Satellite signal.
As for whether or not that’s disrupting sync – if that’s losing GPS Lock, then the AP will keep broadcasting for whatever your Holdoff Time is set to. The clock will drift, without GPS to keep them all regulated. So, right away, a loss of GPS isn’t critical, but depending how long your ‘Synchronization Holdoff Time’ is set to… that AP’s clock will drift more and more - and if you’re using frequency reuse, then YES, that can affect the other ones for sure.
So - two questions to address and fix really:
FURTHER TO THAT THOUGH - there are still lots of ways to have self-interference, even with GPS turned on and synced. GPS is the key to mitigating self-interference and to spectral efficiency… but it’s still possible to have it set incorrectly, or to have it implemented incorrectly. It’s not magic in and of itself. 
Yes I see… All 3 of my towers have been an uphill battle with modulation not being what it should be. I have followed the guide lines set out by Cambium and I still have issues… some have abandoned the epmp 3000 gps for packetflux and as I am using GPS sync on some towers, I am curious as to why the sectors using frequency re use are performing poorly, as I have one tower with 2 epmp 3000 not using frequency re use perform as expected.
But the tower in question is very rural and no other WISP in the area but us. 3 sectors, North, East and West. The East and West are using frequency re use and are 180 degrees apart and are 90 degrees separated from the North respectively.
I will definitely have a look at the wires/connections but the gps puck shouldnt be blocked as it is mounted in the cambium sector antenna at top of tower.
I appreciate the reply!!!
OK - I thought the images above showed 4 AP’s - East, West, North, South? It’s difficult to tell without all the information… but GPS Sync and Frequency Reuse can work very well… but they are not magic. There are ways to screw them up too. The goal is to make sure that the SM’s on each sector can hear it’s own sector at least 30 dB better than it hears the opposing sector… and also that each Sector can only hear it’s SMs at least 30 dB better than it hears any SM’s from the other sector.
Hi. Well, if you want advice with modulation problems, I think there are lots on here who would be willing to help out. We’d basically want to see your
Since this thread is titled “3000L GPS”, I’ll say this about GPS - which is GPS generally won’t have anything to do with modulation problems directly - unless the GPS lock fails, and the AP then starts broadcasting un-synced.
Just been monitoring throughout the day and not seeing much consistency in the gps graph of the epmp 3000…one sector earlier today was doing really well with its GPS, most of the tacked satellites SNR in the green and now its tanked, most of the satellites SNR low to very low.
Thank you ninedd, I will get those together and I think I will start a different thread more focused on modulation.
How does one go about this, what you stated above. I know for sure that the SMs on their respective sector do not hear the opposite sector as the opposite sector is not seen in the SM wireless section. And I do know that the sectors do not see any SMs from opposing sector. Please correct me if I am misunderstanding
