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From: Chuck Simmons
Organization: You jest.
X-Mailer: Mozilla 4.61 [en] (X11; U; Linux 2.0.33 i586)
Subject: Re: How does a mixer work?
Date: Thu, 24 Oct 2002 01:15:10 GMT
NNTP-Posting-Date: Wed, 23 Oct 2002 18:15:10 PDT
John Woodgate wrote:
> I read in sci.electronics.design that James Meyer
> wrote (in email@example.com>) about 'How does a mixer work?', on Wed, 23 Oct 2002:
> > Many (I hesitate to say "most") SSB transmitters generate SSB by using a
> >balanced modulator to (almost) completely remove the carrier and then a filter
> >to remove one of the sidebands. There is no ( well perhaps -80 dB) carrier
> Well, it wouldn't be easy to recover that. But WHY go for such an
> extreme suppression? 20 dB carrier suppression takes up 1 W of a 100 W
> transmitter. How much more range do you get with 100 W than 99W? And a
> carrier at -20 dB can quite practicably be recovered.
> Put half a brick on one side of your DBM to unbalance it a bit.(;-)
Where this is leading is that the carrier is not precisely information
free in that it is intrinsic to the information transmitted and
therefore must always be present to recover the information. That is,
given only a sideband, it is not possible to recover the information in
it unambiguously without the carrier. In the case of voice
communication, it is not so hard to insert a usable carrier at the
receiver by trial and error. In more complex situations, there must be
some evidence of the original carrier in the transmission or the
receiving end must have a priori knowledge of the appropriate carrier.
The latter method is implemented by agreement over a communication
channel meaning that the carrier must not be considered content free.
... The times have been,
That, when the brains were out,
the man would die. ... Macbeth
Chuck Simmons firstname.lastname@example.org
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