All out of ideas - poor upload speeds

We have a tower with six co-located 900Mhz units, running opposed frequencies as so:

SE, NW = 924
S, N = 915
SW, NE = 906

We know there is interference in the 924 band and we are shortly to test a bandpass filter on those APs. Some SMs jump right from SW to N if I reboot the SW AP, instead of the NW, which should give you an indication what I’m talking about.

We’re using MaxRAD connectorized units. Right now on the 915 N we are using a Last Mile bandpass filter, but it hasn’t improved things much (anyone know if there should be a different setting for external filters delay?) The 900Mhz gear is at 280’ elevation on a large bluff, and it is all GPS timed (through a 300’ cable, it should be noted). Using the large non-connectorized panels at that height would not be good…

OK, here’s the issue:

We have 100% download in all cases, but uploads are between 30% and 70% for the most part, and they fluctuate. We have been out with an oscilloscope and it doesn’t appear to be interference (particularly on the 915 frequency) causing our problems but the variation in signal strength is a question. The A.P. panels are more or less vertically mounted but are horizontally polarized (if that makes sense to you). Upload speeds vary between 95Kbps and 450Kbps with the same customer over the course of a day, usually a bit worse at night for some reason.

It’s not timing, they’re all timed. We’ve turned off all but one unit (the worst is N) and there was no change for the subscribers, so that’s probably the best proof that the units are timed and not interfering with each other. The bandpass filter is not improving speeds but it has stopped some of the re-registrations. Even at 11km, these customers are getting 100% downloads and many of them are line-of-sight or near-line-of-sight.

All units are set at 28dbm output. Max range is set to 20 miles. Control slots set to 1, downlink data set to 75%.

We got sidetracked a little on the Frame Calculator today but realized that they are all running Hardware handshaking (tried software, same results) and so no change is required - as well as the fact that we shut all but one AP off and had the same issue.

We’re stumped. Elsewhere, we have 900Mhz units running great. Does anyone have a suggestion for us?

P.S. I know it probably doesn’t help, but we have six 5.7Ghz APs on the same tower at 270’ and performance is awesome but of course, we are limited by distance and heavy foliage.

Take an SM up there and turn it into a spectrum analyser. Breifly shut down the 900 cluster and take a look at the noise on the SM’s Analyser page.

Since you are getting 100% down and 30% up, I would suspect RF interference is blinding the AP’s.

We’ve done this and unfortunately the SMs register no interference.
We also see no major interference on the 915 band anywhere.

It’s a mystery.

It is a mystery and I feel your pain.

Had a problem that was similarly bizarre. We had some breezecom cables that were in place and converted them for use with Canopy. When it rained water was getting in the end of the cable, running down the inside of the cable and pooling at the RJ45 socket on the CMM. The 24V was shorting across the data pins and causing charring. The dropped packets were causing poor performance.

I would go up when the road dried up a little, and by the time I got up there the water would dry up in the CMM and the network would start working fine again. Drove me nuts. Finally wiggled the cables and heard the crackling. Replaced the CMM and the problems cleard up. fixed the cable issues also.

Perhaps you might consider:
double checking that all the AP’s are receiving GPS sync
Shutting down AP’s one at a time to see if one is defective
re-terminating all of the RJ45’s

Failing the above change out the CMM (if it’s common to the 6 AP’s)

Let me know…

Jerry Richardson wrote:
double checking that all the AP's are receiving GPS sync

Yes, they all report that they have sync.

Shutting down AP's one at a time to see if one is defective

We shut them all down but one and still had the issue.

re-terminating all of the RJ45's

I would do that, but I don't see how that could cause the RF issue we are seeing. As you know, on a 280' tower that is a great deal of work. :(

Failing the above change out the CMM (if it's common to the 6 AP's)

It is, and I think it's something we will try.