NPR: Tests Show Substantial Number of FM Modulators Exceed Emission Limits

NPR: Tests Show Substantial Number of FM Modulators Exceed Emission Limits
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(This story and all content is copyright Radio World.) In a new study of FM modulators intended to study “real-world” conditions, NPR Labs says the measured field strength of about one-third of the consumer devices exceeded Part 15 emission limits.
This is separate from a recent study released by the NAB on the same topic. Broadcasters have complained that the modulators, installed in cars to allow consumers to hear satellite receivers and audio devices over their FM radios, cause interference to surrounding motorists.
NPR Labs took measurements from more than 28,000 moving cars on two channels. In a study to measure the field strength of signals on 88.1 MHz and 87.9 MHz emitted from a variety of highways in the Washington area, NPR Labs found nearly 1% of the 5,000 car average on each highway measured had operating FM modulators on the two channels. “Of these, approximately on-third are operating with emissions that exceed the regulatory limit,” states NPR Labs.
John Kean of NPR Labs told RW Online that between the NPR and NAB tests, “We’ve answered key questions” about FM modulator use. NPR is passing on the results to the North American Broadcasters Association, a member of ITU.
Read more in an upcoming issue of Radio World.

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NPR Finds Objectionable Interference

NPR Labs has conducted what it describes as a real-world test of how FM modulators are used, to determine how much signal leakage from the consumer audio adapters is affecting the lower part of the FM band.