From: email@example.com (Gibbo)
Date: 22 Oct 2002 15:34:00 GMT
Organization: AOL, http://www.aol.co.uk
Subject: Re: How does a mixer work?
"Kevin Aylward" firstname.lastname@example.org wrote:
>"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?
It means they haven't had a power failure at the transmitter. It means the ship
hasn't actually sunk. It means the plane hasn't actually crashed. Perhaps silly
arguments, but information nevertheless.
> 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.
Perhaps you use the term "information" in some technical form that I do not
know. In general English useage the presence of an unchanging carrier (or
sideband) can and does carry information.
Not trying to be awkward. Just making a point that all that wonderful maths
isn't quite as definitive as some seem to think.
>SuperSpice, a very affordable Mixed-Mode
>Windows Simulator with Schematic Capture,
>Waveform Display, FFT's and Filter Design.