This document provides questions and answers for wireless point-to-point troubleshooting.
A. Locate the source of the interference. In order to do so, look around at both ends of your link. Do you see any other antennas or related equipment? If you identify other nearby radio equipment, try to learn:
Who operates it
Who owns it
What frequency or frequencies it operates on
With how much power does this other equipment transmit
What kind or type of antenna polarization is in use
See if you can contact the owner or operator of this other equipment to find out:
When you have confirmed the type and location (and other details) of the interfering radio equipment, you can figure out a solution. Start with your antennas.
Change the polarization of your antennas to be opposite (crossed) to the polarization of the interfering system in order to solve the problem. You must first ensure that your systems antennas are cross-polarized to the other systems antennas, because this solution is so effective and requires the least cost and effort to implement.
If the problem persists, change the frequency of one of the systems (probably your own). Systems that are not on (or close to being on) the same frequency rarely interfere with each other. If the interferer is very high-powered (such as radar), interference can still occur because the powerful interferer overloads the receiver, and causes interference-like symptoms. Change of frequencies is usually effective.
Note: This solution is only appropriate in the case of systems that operate in unlicensed bands, where the use of a specific frequency is not necessary. This solution option is typically not available to licensed users, although such users are not likely to encounter interference that they can solve this way.
Sometimes, you need to change frequencies for both your system and the interfering system, in order to maximize the frequency separation.
In order to change the frequency of your system, swap the transmit and receive frequencies. This process requires removal and reinstallation of both of your duplexers, in order to turn them around to accommodate the now-reversed TX/RX frequency split. You do not need to make any other adjustment or re-alignment of the antennas. You can try this when you experience interference at only one end of your link (the most common situation), because the link end where the receiver was receiving interference now transmits on that frequency. In other words, only receivers can experience interference!
You must use the final tool to alleviate an interference problem only after you have unsuccessfully tried all the others. That tool is antenna gain. For antennas, higher gain is virtually synonymous with narrower beamwidth. When you change antennas to higher-gain, lower-beamwidth types your system becomes less able to see the interferer, and this step sometimes solves the problem.
Note: Usually only one end of a link experiences interference. Therefore, you only need to change the antenna at the link end where the receiver experiences the problem. Changing antennas is the most costly and time-consuming solution. Therefore, install antennas of adequate gain (narrow enough beamwidth).
If you decide to replace one or both antennas with higher gain units, verify that the TX power needs to be adjusted downward to ensure that the radiated TX power (EIRP) still complies with the applicable FCC rules.