Reply-To: "Kevin Aylward"
From: "Kevin Aylward"
References: <7Tbt9.2176$R24.email@example.com> <firstname.lastname@example.org>
Subject: Re: How does a mixer work?
X-Newsreader: Microsoft Outlook Express 6.00.2800.1106
Date: Tue, 22 Oct 2002 15:58:37 +0100
NNTP-Posting-Date: Tue, 22 Oct 2002 15:58:43 BST
"Gibbo" wrote in message
> "Kevin Aylward" email@example.com wrote:
> >> If you insist in filtering the carrier with an almost infinitely
> >narrow filter
> >> to prove that it is useless then try the same thing with one of the
> >> and see how much information you can get out of it.
> >But this misses the point. A channel of zero BW cannot carry any
> >information, i.e. H = BW.log(1+S/N) bits/sec. By assumption, the
> >sidebands are varying, or obvously, they dont carry an information.
> They can tell you whether or not there is a modulating signal.
> information. No amount of maths "proving" otherwise can change that.
The idea being the definition of information is the ability to use such
information constructively. As far as transmitting, for example, a
random data stream, a continuous sideband is useless. Sure, you might
know it on, but so what? What use is this? If you say it can tell you
that it is not off, this means nothing, unless you can also have it in
an off state as well at some point. That is, if it has two states, it
has log2(2), i.e. one bit of information. However, in this case the
system BW cannot be zero, otherwise it would take infinite time for it
to change from one state to another.
Unfortunately, your concept of "information" is not very fruitful, and
no one, and I mean no one, doing serious work in communication theory
and systems uses it.
SuperSpice, a very affordable Mixed-Mode
Windows Simulator with Schematic Capture,
Waveform Display, FFT's and Filter Design.