[AMRadio] Physical Reality of Sidebands


Bob Bruhns bbruhns at erols.com
Sun Jan 16 16:54:15 EST 2005


I contend that we are synthesizing a double-sideband with carrier signal
when we modulate amplitude by varying PA B+, or by other means.

You can draw a graph of the carrier, upper sideband and lower sideband sine
waves (of course you must make the relative timing/phase correct), and add
them together, and the resulting composite signal will be identical to the
modulated signal we produce with our modulated stage.  Therefore I conclude
that they are the same; that the sidebands exist, and that the carrier is
continuous, even though the composite signal may vary from 0 to 2x the
carrier level.


----- Original Message ----- 
From: <W7QHO at aol.com>
To: <k4kyv at hotmail.com>; <amradio at mailman.qth.net>
Sent: Sunday, January 16, 2005 4:12 PM
Subject: Re: [AMRadio] Physical Reality of Sidebands


> Sounds to me like the old question as to whether or not a tree falling in
a
> forest makes a crashing sound if there is no one around to hear it.   In
> answering such a question one has to draw a distinction
> as to whether "sound" exists only as the reaction of the human auditory
> system to pressure waves in the conducting medium (air in this case) or,
do these
> pressure waves themselves constitute "sound."   Don seems to be saying
> sidebands exist only exist as a "physical reality" when apprehended by a
human
> observer through the reactions of some kind of instrumentation (narrow
receiver,
> etc.).    Seems like a philosophical rather than an engineering issue to
me.
>
> Dennis D. W7QHO
> Glendale, CA
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