IM Check Procedure

1. Determine if there are any co-located transmitters at this facility.
2. Collect information on each of the following transmitters:
■ Antenna types
■ Emission type
■ Transmit power
■ Location of antennas
■ Operator of equipment
■ FCC license number
3. Conduct an intermodulation study report looking for hits in your own
band or in another band based on the nature of the problem.
4. Allocate sufficient time to review the report.
5. Determine if there is a potential problem.
6. Formulate a hypothesis for the cause of the problem and engineer a
solution.
Based on the actual problem encountered, the resolution can take on
many forms:
■ Is the problem identified feasible?
■ Can the problem be resolved through isolation alone?
■ Is the problem receiver overload-related?
If the intermodulation product is caused by the frequency assignment at
the cell site, then it will be necessary to alter the frequency plan for the site,
but first remove the offending channels from service.

If the intermodulation problem is due to receiver overload, the situation
can be resolved by placing a notch filter in the receive path if it is caused by
a discrete frequency. If the overload is caused by cellular mobiles, using a
notch filter will not resolve the situation. Instead, mobile overload can be
resolved by placing an attenuation in the receive path, prior to the first preamp,
effectively reducing the sensitivity of the base station receiver.