Interference to DTV Reception from FM Radio Signals

Interference to DTV reception has been observed in the High VHF Band 174-216 MHz. This interference is due to second order non-linearity in the affected receiver front-end. This non-linear distortion shifts signals from the FM band (88 - 108 MHz) into the High VHF Band where they act like in-channel noise. These distortion products are: the second harmonic of each FM signal and the sums of each pair of FM signals generated in the mixer by the power of these FM signals at the RF input port of the mixer. The RF selectivity of DTV Down-converters tested by the author did not suppress FM signals and loss of DTV reception resulted on one or more channels. This inter-band interference (FMI) had not been anticipated in the planning process for the DTV service. Experimental procedures used by the author and his test results are presented. In addition to FMI in DTV down-converters, it is likely that some DTV receivers, broadband RF signal distribution amplifiers, Low Noise Pre-amplifiers, and "amplified indoor Antennas" also generate FMI.