While looking for signals that don’t belong on the input to a receiver, it’s important to know what signals are typically present in the bands, as well as what other legitimate signals may be present. This can save much time when hunting signals. If this is not possible, the signal can be demodulated so the user can listen for the station ID call sign.
Many interfering signals are not so easy to identify, so field engineers must find them by hunting. Possible interference causes to seek are on-channel interference, in-band interference, impulse noise, harmonics, passive intermodulation (PIM), or intentional interference caused by a jammer.
Locating the source of interference
Once an interfering signal has been spotted and characterized using the tower’s antenna, the next task is to find the same signal using a ground level antenna. This will allow the field engineer to search for the signal, either by direction finding or seeking areas of higher signal strength. One issue is that signals that may be strong atop the tower may be weak at ground level.
Initially, it must be determined if the signal is visible near the tower base. If it is, the signal has been spotted at ground level and it’s time to move to the next task, locating the source. If not, there are several things to attempt:
- Check other