Wednesday, November 4, 2009

Ron H. Re: Expanded Band Stations

I think there is a low power limitation for all AM broadcast stations operating on 1610 KHz or higher. The local station in Chicago was operating 10 KW during the day, but they were required to reduce their power to 1 KW at night on their 1690 frequency. They continuously claimed they were applying to the FCC for authority to use 10 KW at night. The station changed format; therefore, I lost interest in following their fight for more power. The whole idea of having an expanded band was to give some low and medium power broadcasters a chance to have a signal without having nearby competition on the same frequency. I remember reading all of the stations in the newly expanded part of the AM band were going to be required to run AM stereo. It seems that requirement has been forgotten. There is another point of relevance: they could not be authorized a frequency which was twice the frequency of any other local station because of the possibility of harmonic interference. As an example, 1700 KHz could not be licensed if there is a station in the same area operating on 850 KHz. This seems strange to me because I thought harmonic radiation was not a huge problem in the AM broadcast band. I won't try to explain image frequencies, but they are a problem caused by a deficiency in the typical AM receiver. These phantom signals usually appear 910 KHz above the station's actual transmitting frequency. One might hear these phantom signals on his or her radio if it is tuned to the upper end of the band, and there is a local station operating in the lower end of the band. There is a good explanation at .

It is my guess receiver image frequencies would be more of a problem than harmonic radiation from today's sophisticated transmitters. Any comments are welcome?

Ron Henselman W9FT Melrose Park

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