Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!purdue!ames!ucsd!sdcsvax!ucsdhub!hp-sdd!robert
From: robert@hp-sdd.hp.com (Robert Navarro)
Newsgroups: sci.electronics
Subject: Re: Stereo vs. Mono: Q about AM Stereo
Message-ID: <1972@hp-sdd.hp.com>
Date: 4 May 89 17:45:58 GMT
References: <4046@bgsuvax.UUCP> <21000021@m.cs.uiuc.edu>
Sender: news@hp-sdd.hp.com
Reply-To: robert@hp-sdd.hp.com.UUCP (Robert Navarro)
Organization: Hewlett-Packard, San Diego Division
Lines: 50

In article <21000021@m.cs.uiuc.edu> irwin@m.cs.uiuc.edu writes:
>
>/* Written  3:41 pm  May  2, 1989 by robert@hp-sdd.hp.com in m.cs.uiuc.edu:sci.electronics */
>In article <4046@bgsuvax.UUCP> klopfens@bgsuvax.UUCP (Bruce Klopfenstein) writes:
>>He wants "proof" that stereo is superior to mono.  You can laugh, but I have
>
>In the above, Robert indicates that AM radio is restricted to 5KHZ.
>The way I figure it, it is 10KHZ.
>
>On the AM broadcast band, there is a station frequency every 10KHZ, starting
>at 550 and going up in increments of 10 to 1600. If a station were at 760KHZ,
>they would have space 5 below center frequency and 5 above center frequency
>for their lower and upper sidebands. This is a total of 10 in width.
>
>True, each sideband is limited to 5, so, they need to used single sideband
>and gain 5MHZ in band width, they have the space there, it is just not
>being utilized to the best advantage. SSB is still AM, I wonder if the
>FCC would allow it? It would take several years to junk out all of the
>old AM receivers, maybe 25, but, they would eventually disappear, and,
>if you wanted the home radio to get either mode of transmission, you
>may be inclined to upgrade sooner, as the SSB receiver has to reinject
>the carrier locally, so demodulation can take place.
>
 I think you misunderstood me when I said that AM is restricted to 5khz.
What I meant was since the space between stations was 10khz and since 
envelope detection is used for demodulation, each 5khz sideband of the 
transmitted signal is mirror image copy of the other. If the transmitted
AM modutated signal is limited to 10khz, then the baseband signal is
5khz. Now, I have been told that in LA and San Diego, some stations have
obtained permission to transmit a baseband signal of 10khz, but that
means that they are taking up 20khz of the AM spectrum. These are
probably the stations that seem to take up a large portion of the AM dial.

You are correct there is a 5khz sideband above and below the center 
frequency, but in the current AM scheme, these sidebands contain the 
exact same information. SSB AM would be a much better system 
especially since the coherent detection required also gives a slightly
better signal to noise ratio -- but the cost of the receiver is greater
for coherent dectection. Modern electronics may make this cost negligible
but I am not sure on that point.
   One of my main points about AM Stereo is that trying to fit in with
the current AM scheme is going to cause some tradeoffs with AM stereo that
are bound to effect it's performance or cause less bandwidth to be
availiable in the AM band.
 
Robert Navarro
HP San Diego
 
-- 
Robert Navarro