Hello guys,
I have an issue on one new ePMP 1000 GPS Sync.
The GPS can't track satellites.
Can you help me?
Here's what I'm seeing:
Hi giuseppe4,
It appears that the satellite signals are very poor or there is high interference at the GPS frequency (1.6 GHz) or one of its haromonics. Are you using the external GPS puck antenna? If not, please use that. If you are using it, please try to position it at a different angle or location on the AP, antenna or mount. Remember the GPS antenna needs to have clear view of the sky. Some customers have had better satellite reception by pointing the Cambium logo on the GPS antenna towrds the south sky (if you are in the northern hemisphere). Lastly, do you know if there are other UMTS/LTS gear nearby? Depening on what frequency they are operating on, they could be wiping out the GPS signal (as shown by 0 SNR on all the satellites). For example, if there is an UMTS repeater operating at 800 MHz and situated on the same tower as your AP, its 2nd harmonic could be interfering with your GPS signal.
Thanks,
Sriram
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Hi Sriram,
Thank you for your answer!
I mounted two ePMP on the same site, the ePMP External GPS (I used it) are one next to the other.
The other ePMP has full GPS reception, this one hasn’t.
I’ll try different position of the GPS receiver, but… What can I check?
There are other antennas in that site, and I think also 800MHz cellular, but this doesn’t explain why the other receiver works perfectly.
They both have clear sky view!
I’m in Italy
@giuseppe4 wrote:
Hi Sriram,
Thank you for your answer!
I mounted two ePMP on the same site, the ePMP External GPS (I used it) are one next to the other.
The other ePMP has full GPS reception, this one hasn't.
I'll try different position of the GPS receiver, but... What can I check?
There are other antennas in that site, and I think also 800MHz cellular, but this doesn't explain why the other receiver works perfectly.
They both have clear sky view!
I'm in Italy
Hi giuseppe4,
It is odd that one of the radios has good reception while the other one doesn't. Are the GPS antennas for both radios facing the same direction? I'm wondering if one of the antennae is isolated from the celluar antenna. I'm almost convinced the cellular system is wiping out your GPS reciever. I would try positioning the GPS antenna in different angles and positions. I would even try removing the external GPS antenna and letting the internal patch antena on the GPS chip take over. Sometimes, the patch antenna may not hear the celllular noise as well and may be able to lock on to the satellites. Remember that the radio needs to be able to track at least four satellites to achieve a 3D lock. You shouldn't have a problem tracking 4 GPS satellites in Italy (you already have 12 visible) as long as you have clear view of the sky and work around any cellular interference.
Thanks,
Sriram
1 Like
I'd suggest swapping the GPS antennas if you can do so without too much difficulty, see if the problem follows the antenna or stays with the same AP. If it follows the antenna then (obviously, at that point) replace the antenna, otherwise dig deeper on the GPS and AP itself, which might need an RMA. (if it were our tower, I'd send someone up with a replacement GPS antenna and a replacement AP, first swap GPS antennas, if that fails swap APs and diagnose later)
j
2 Likes
newkirk, I'm doing exactly as you suggested!
Tomorrow I've planned exactly that with our guys... I'll keep you updated :)
Thank you for your answers!
Hello,
I solved the issue I had on this tower by changing GPS position.
The problem is LTE/UMTS for sure, because I had this issue on all towers with LTE radios on 800MHz.
Is a solution for that?
I have some towers near LTE cells (or co-located with LTE radios) and it's very annoying to have unstable GPS Sync.
I partially solved the issue by shielding the GPS cable, but I would like to have something more "official".
Anyone? Cambium?
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I think you'll find what I found. You can try out PacketFlux, but that also uses GPS for sync. The idea is that GPS antenna is not passive, so it could fight off interference from the cellular. Otherwise, you're stuck with using a CMM, which will certainly fix the issue.
1 Like
Thank you Cory!
PacketFlux seems to be very interesting... If I understood correctly, I have to purchase one Gigabit SyncInjector SyncPipe Basic and then select "CMM" as Sync Source on the ePMP?
Did you try it? Does it work?
guiseppe4,
I believe you're right in what you've said. I can't confirm however since we haven't actually decided which route to take for this site to mitigate our GPS issues. I know that Sri could give you a more firm answer. He was very helpful in our conversation regarding GPS issues.
Our issue was not as severe as yours, but still a problem. At random, the SNR on all of the tracked satellites would plummet to the single digits and caused radios to lose sync. I'd be curious which hardware you choose and your results.
2 Likes
So, waiting for Sri answer! You were very helpful!
@giuseppe4 wrote:
So, waiting for Sri answer! You were very helpful!
Hi guiseppe4,
You have done all the right things. Cory has some good advice for you as well to get past this problem. Unfortunately there's only so much we can do against the high powered cellular radios operating at 800 MHz. Their harmonics are just too strong especially when collocated on the same tower. Cory's suggestion to try Packetflux or CMM4 is very good. Alternately you can try an GPS puck antenna with slightly higher sensitivity such as this one: http://www.synergy-gps.com/index.php?option=com_content&task=view&id=147&Itemid=114
Ultimately, with repositioning the GPS antenna, shielding it and possibly using a higher sensitivty antenna could solve your issue. It appears you have already done that. Your other options are to use Packetflux or CMM4s.
Thanks,
Sriram
2 Likes
Hi Sriam, thank you very much for your answer!
Could you post the datasheet of your GPS puck antenna (N000900L005A) so I can make a comparison between others and yours?
Is there some special feature the GPS puck antenna must have?
Unfortunately in Italy I can't find the GPS antenna you suggested... :-(
Can you suggest a better shielding?
I opened a CAT7 cable and I used its shield around the GPS cable.
In some cases it worked, but not in others, even if on the same tower, but on different heights.
I think Cambium should include a better shielded and better performance GPS antenna puck in the ePMP!
Hi everyone,
Unfortunately I’m still having some issue with GPS and I decided to try PacketFlux.
Is the sync the same as GPS units? I mean: will other devices that I can hear from the AP, synced using the internal GPS, sync to my tower which use PacketFlux?
Thank you
I asked to PacketFlux directly and they answered:
We make sure that our GPS sync pulse is the same as Cambium’s. So yes, the internal GPS will absolutely work with our devices, specifically the Gigabit SyncInjector.