[Elecraft] [K3] Hearing aids, meet K3

[Jim Brown]

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