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NNTP-Posting-Date: Sun, 20 Oct 2002 20:54:15 -0500
From: "John Fields"
References: <email@example.com> <firstname.lastname@example.org>
Subject: Re: How does a mixer work?
Date: Sun, 20 Oct 2002 20:48:14 -0700
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"Dbowey" wrote in message
> What information is being impressed on the carrier? (none).
The amplitude of the carrier is being made to vary at a rate which
corresponds directly to the amplitude variations of the modulating signal.
This change in amplitude is the information which is being impressed on the
carrier and which is later extracted by detection. A prime example would be
a crystal radio with a bandwidth unable to discriminate between the carrier
and the sidebands, but which still rectifies the carrier, recovers the audio
envelope with a little lowpass filter, and sends the recovered information
into your ears with an electromechanical transducer of some kind.
> In the process of
> modulation, sidebands at frequencies other than the carrier frequency are
> generated and the net change to the carrier is.... nothing. It is
> serves only as a reference for detection or demodulation of the
OK, let's say that's true and that we're doing something like grid
modulation, where the amount of power required to modulate the carrier is
Now, let's say that you turn on the transmitter and you're sending out 100
watts, CW, with no modulation.
Now, turn on the modulation and create the sidebands. Where do you think
the power in them comes from? Since the power contributed by the modulating
source was miniscule (remember, _grid_ modulation) then it must have come
from the carrier. if it comes from the carrier, then the amount of power in
the carrier itself must be decreasing when the sidebands come into
existence, since the total amount of power available was 100 watts. If the
carrier is diminished because of the creation of the sidebands, then the net
change in the carrier is.... something.
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