[78-L] AM radio--WAS: acoustic recording

[Steven C. Barr]

----- Original Message ----- 
From: "Michael Biel" <mbiel at mbiel.com>
> I do take exception to David's contention that broadcasting has limited 
> frequency response.  FM mono extends to 20 K and FM stereo extends to 15 
> K.    I don't know about Canadian law, but I do know that in the U.S. 
> there was no upper limit on frequency response on AM until the late 
> 1990s.  Before then it was routine for AM stations to have response 
> beyond 10K, usually uip to 13 or 14 K.  The limitations in AM sound is 
> due to the lousy radios made since the mid-70s.  Radios from the 50s and 
> 60s are much better before manufacturers purposefully reduced their 
> bandwidth because of increasing interference from new short-spaced 
> stations.  Top response now is allowed to 10 K and must be filtered 
> beyond that.  There are only a couple of radios made today that can meet 
> that response, such as the GE SuperRadio 3 and the Grundig S-350, but 
> the stations are broadcasting to 10K, at least here in the U.S.  
> 
How is that wide response possible for AM broadcast? An AM signal
has "sidebands" equal to Fc (the centre frequency) + AND - the modulating
frequency...am I right here? Therefore, if a 1000KHz signal is modulated
with a 14KHz sound, the sideband signals generated would be 1014
and 986 KHz...both well outside the station's assigned bandwidth...and
interfering with broadcasters assigned frequencies of 1020 and 980 KHz...?!

Steven C. Barr