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#11
June 27th 05, 04:47 AM
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Nice website!
Pete "Richard Fry" wrote in message ... "Pete KE9OA" ....it would be very difficult to have a standard preemphasis curve for AM stations, because there are so my receivers with different characteristics because of different I.F. bandwidths and different rolloff characteristics in the audio chain. ______________ In the US, broadcast AM pre-emphasis is defined by a voluntary standard of the Nat'l Radio Systems Committee. The tx audio response is a modified 75 us curve. The curve has an 8700 Hz break frequency to reduce adjacent channel interference. The NRSC standard expects the amplitude response of the narrow RF/IF bandwidth of "typical" MW broadcast receivers to restore ~ flat system response, not that a network complementary to that at the tx be added to audio circuits following the 2nd detector. However that is not prohibited -- it is just more expensive. Also, that approach to implementing AM pre/de-emphasis would not be "backward compatible." RF (retired broadcast field/systems engineer -- RCA & Harris Corp) Visit http://rfry.org for FM transmission system papers. |
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