great signal, bad link test

We have 900 omni antenna with an access point. There are 30 clients on this particular AP. All 30 clients have a great signal but 17 of the SM are getting very poor link test. Downlink is around 80 and uplink is around 40-50. We are going to try and do spectrum analysis around town to see if there is interference and then see if we can track it down. We have changed out everything in the way of hardware. We have changed frequencies to everyone available, 906-924.
Also, if it turns out that there is interference, what can we do about it?
Thanks in advance for any help.

Tell them to throw away their 900 MHz cordless phones. That is a possibility.

An Omni is a double edge sword. You get alot of coverage but low EIRP at any given point on the compass reducing your range. Also, the AP sees all of the noise which can de-sensitize it’s ability to see AP’s.

The ideal solution would be a CMM with 6 AP’s with 60deg antennas, but that is a good chunk of change.

An alternate solution would be to go to 3 AP’s with 120deg antennas. This will increase your effective power and be somewhat less prone to interference.