3 Sector Cluster 900Mhz

Recently put up 3 900Mhz APs using 120degree 10.5dBi Sectors (SuperPass).

I’m seeing on some of the installs/surveys for people in this area great downlink test results, but lower than average uplink results.

Typically, I’ll see 95-100 downlink, 30-70% uplink.

Some background on my setup right now…

Tower is 110’ AGL
3 APs are set to generate sync.
NO CMM is used (at this time)
Each AP is set to a non-overlapping frequency. (906,915,924)
APs are running 7.3.6 software Hardware Scheduling and 2x rate.
SMs are running 7.3.6 software, Hardware Scheduling and 2x rate also
Antennas are SuperPass.

First question: Does this sound like self-interference at the tower side?
Second question: Is this a problem caused by no CMM/GPS sync to the APs?
Third Question: Are SuperPass antennas decent?
Fourth Question: Is this moreso a problem with the 120 sectors?

I had shut off 2 of the 3 APs and ran a test at an install and saw marginal performance increase on the uplink test to 89% (1x mode)…

This particular test case is roughly 4.5miles from the tower and moderate foliage (clump of trees in the distance). I have 3 other subscribers on this setup (2 subscribers on 1 AP and 1 other subscriber on the AP I’m having difficulties with at this time).

Here is a radio mobile graph of customer to tower:

larger picture

Sorry for the lengthy post, hopefully it was informative enough and thanks for the replies in advance!


Turn all AP’s off, and then one at a time put them in SM mode and measure the noise floor. This will let you know if what you are even trying to do (provide coverage) is a good idea. Second, go out where your subs are and use the SM in analyzer mode and get an idea of your noise floor. You should be able to average the numbers to get an idea of how many dB you need to be above…

Second, the way you have your system doing sync is not going to work. Just because they are all generating sync doesnt mean that they are all sync’d.

All the transmitters must turn on at the exact same time so they do not clobber each others frames (remember, canopy is a TDD based system)

You need to have something generate a pulse, and pass it on to the others. I never have tried 3 AP’s from one AP… I would look into a SyncPipe with a SyncInjector. All said and done you should be at around $300 plus shipping and cabling.

3 AP cluster without sync…???

You are walking all over yourself and any body else in the area. (if that is an issue.)

Sync allows all APs to TX and RX at the same time, this is imperative for coexistence on the same space.

CMM or SyncPipe are a must in this application.

Good Luck

During a call to Motorola Tech, I had asked if I would be able to utilize 3 APs on one tower without a CMM in 900 band using 906, 915, 924 and was told it would work. (It is possible the tech did not understand my situation/question, and could not have made a well informed decision regarding it working correctly…)

My plans are to get a CMM up there, as I have one right now, and test it out returning to a few trouble customers and re-running tests.

The noise floor at the tower is extremely quiet, sitting in -95 range all the way down the board for the most part. Likewise at a few customer locations with troubles (minus seeing the AP).

I’ll report back what I find.

Thanks again,


If this is your only tower and there are no other 900 AP’s within about 10 miles, you could not use a CMM using this procedure:

Set one AP to generate sync
Carry the sync on the RJ11 pins 1,2,3,6 to the other 2 AP’s
Set the other two AP’s to receive on the timing port.

Confirm DL%, Max Distance, and Control slots are the same on all three AP’s.

Of course if plan on adding more towers, then the CMM should go in now.


Do you mean that I should make a Y adapter to connect these 3? I’m a bit confused on the wiring aspect.
AP1 -> AP3
AP1 -> AP2

Or does this need daisy chained?


Thanks again!


Split or daisy chain, does not matter. You just want to connect all three radios RJ11 pins 1, 2, 3, and 6 together.

AP1 --> AP2 --> AP3


AP1 --> AP2