[BC] Re: SUPER MODULATION & AM STANDARDS

[DANA PUOPOLO]

The 125% limit was put into effect because of splatter.  Stations that
supermodulated (especially ones near the top of the dial) used to splatter
like crazy, wiping out most stations within 20 or 30 kHz away. I remember 1510
in Boston being 1/2 an inch wide on my Mustang car radio's dial. This was done
on purpose to have dial dominance.

-D



------ Original Message ------
Received: Sat, 14 May 2005 10:29:46 AM PDT
From: "Phil Alexander" <dynotherm at earthlink.net>
To: Broadcast Radio Mailing List <broadcast at radiolists.net>
Subject: Re: [BC] Re: SUPER MODULATION & AM STANDARDS

On 12 May 2005 at 10:18, Lamar Owen wrote:

> So it's not really an interference issue in the positive modulation 
> direction; it's a sidestepping of coverage limits.  You raise the sidebands

> up and you get more distance to effective reception.  And you walk on your 
> co-channels' sidebands, as well as you first adjacents' carriers.

Back in the days when the FCC Broadcast Bureau was run by Harold Kassens, I
think you might have gotten a different opinion regarding the fact that it
WAS an interference issue. This probably was the reason for the RM that led
to the limit of 125%, a truly insignificant amount from an interference 
standpoint in the adjacent channel consideration. Remember that there was
no NRSC frequency limit in those days and modulation in the 12-15 kHz range
was relatively common in most plants. There was a time when adjacent channel
interference was taken quite seriously. Alas, there are few today that recall
those times and none of them are on the Commission.

Phil Alexander, CSRE 
Broadcast Engineering Services and Technology 
(a Div. of Advanced Parts Corporation) 
Ph. (317) 335-2065   FAX (317) 335-9037




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