On 11/01/2013 05:02 PM, George Danner wrote:
Guys, AM Broadcasting isn't your grandmother's AM radio of old. Many years ago, along came NRSC and it's 10kHz brick-wall filter
FCC regulations [73.44 (b)] for AM broadcast stations require the emissions to be at least 25 dB down from the un-modulated carrier at frequencies greater than 10.2 kHz from the carrier. Back in the days of analog filters it was difficult to get much more than 5 kHz bandwidth and still guarantee at least -25 dB at 10.2 kHz. Now with digital filtering you can get out to almost 10 kHz and still meet the spec.
For comparison, the audio bandwidth of FM stations is 15 kHz and the audio tends to have much less distortion (which is generated mainly in the receiver's AM detector).
Since AM stations in the US are spaced 10 kHz apart, a station whose modulation extends +/- 10 kHz from the carrier will heavily interfere with the channels above and below it. Supposedly the FCC assigns channels in such a way that stations in the same area are not adjacent, in order to reduce interference. But of course that does not work at night due to long-distance skip propagation.
Alan N1AL ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
