1 FM Blanketing Interference: a Case Study of Problems and Solutions for a Typical High Power FM Station
1 FM Blanketing Interference: A Case Study of Problems and Solutions for a Typical High Power FM Station Thomas M. Eckels, P.E. Hatfield & Dawson Consulting Engineers, Inc. Seattle, Washington ABSTRACT FM broadcast stations in urban areas often operate from and TV signals and cause undesired signals to be transmitter sites which are either surrounded by residential introduced into home electronic equipment (e.g. broadcast development or are being encroached upon by residences. audio on a homeowner’s telephone). Within the area close to a high power FM transmitting The typical blanketing interference problems and facility blanketing interference is very likely, affecting solutions described in this case study were drawn from radios, television sets, and other consumer electronic the author’s experiences in resolving blanketing devices exposed to the high field strength levels produced interference complaints for Non-Commercial FM station by the transmitter. This paper describes the FCC’s rules and KVTI(FM), Tacoma, Washington. policies with respect to blanketing interference, the kinds of consumer electronic equipment typically affected by blanketing interference, the types of interference produced FCC RULES AND POLICIES within the blanketing contour, and the technical and “public The FM Blanketing Rule relations” measures which have been effective in ameliorating the effects of blanketing interference. The present FM blanketing rule, §73.318, was adopted in October 1984, by Commission action in Docket 82-186; the rule became effective January 1, 1985. The pertinent INTRODUCTION part of the §73.318 reads as follows: Blanketing interference is a general term which refers to the (b) After January 1, 1985, permittees or licensees interfering effects of very strong AM, FM or TV signals who either (1) commence program tests, or (2) produced in the vicinity of a high power transmitter.
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