Evaluation of External Filters in Reducing Type B1 and B2 FM BroadcastInterference to VHF Communications Avionics Receivers

摘要

Commercial FM broadcast stations radiate high power signals in commercialairspace that can produce type B1, third order intermodulation products, interference in the aviation very high frequency (VHF) communications band. It has been proposed that passive, external filters may be a possible solution to this problem. Tests performed on three passive, external filters at the Federal Aviation Administration (FAA) Technical Center are described. These tests compared avionics transceiver performance both with and without the filter installed and were performed in a controlled laboratory environment, using eight avionics transceivers. It was found that passive, external filters can reduce interference effects due to Type B1 intermodulation in some cases. However, this was only a technical investigation of the filters and as such did not consider other issues; e.g., (1) certification requirements, (2) cost versus benefit, and (3) environmental operating conditions. These issues must be fully evaluated prior to any installations.