On 8/7/2013 8:39 AM, Ron D'Eau Claire wrote:
So if you enjoy music on your A.M. radio, note that it's unlikely your radio is reproducing much of anything above 5 kHz.
99.99% of AM broadcast receivers have audio bandwidth of less than 5 kHz. The only ones I know of with bandwidth greater than 9 kHz are the GE Super Radio, the Carver TX-11, and a couple of models made by McKay Dymek, and all of them are long discontinued. I have a Carver and several of the GE Super Radios. In the early 80s I was selling the McKay Dymek radios to broadcasters for use as monitors, and had one at home for a while.
Beginning more than 30 years ago, consumer radios were built to use the same detector and audio circuitry for AM that they used for FM, which includes 6 dB/octave de-emphasis starting around 1 kHz. This equalizes for the pre-emphasis applied at the transmitter, which was, and still is, the standard for FM broadcasting. This made AM even muddier than it already was, so AM broadcasters adopted the standard of applying pre-emphasis to their signals. I don't remember when that was adopted, but I'd guess at least 30 years ago. As I recall, that standard also required a low pass around 10 kHz.
73, Jim K9YC ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
