Subject: Re: missed you

From: Christopher Rose <[email-masked]>
Date: Thu, 6 Mar 97 21:49:51 EST

Hi Jude,

Sorry, but I won't be in tomorrow.  As for communications, it's really
very simple. The trick is knowing what is really important.

For example, the sifting property of impulses is really important
and so is the bit about duality and multiplication in time domain
mapping to convolution in frequency and vice versa.  It you know
those basic properties COLD then you're way ahead of the game
in AM (and NBFM) modulation.  You should know in your sleep
at 3am that the transform of cosine looks like goal posts at
the frequency of the sinusoid.  Likewise, you should know that
sine looks almost the same, but with one of the posts pointing down.

By the way, the sifting property is the one with an impulse
when convolved with anything else gives a shifted
version of the "else" it was convolved with.... for example

delta(t-t_0)*g(t) (where * is convolution) gives
g(t-t_0) as a result owing to the sifting property.

Thus when we multiply g(t)cos(w_0 t) you get something that looks
like  G(w-w_0) + G(w+w_0) in frequency domain because you convolve
G(w) with two goalpost delta functions.

In any case, almost all FM and AM modulation can be boiled down to a
few linear systems facts (there are a few others like the properties
of transforms of real signals... conjugate symmetry...  which are
useful for singl=sideband AM... but it's not a large number of facts).
You could start by asking me some specific questions.  It's MUCH
easier to use email since I'm not in and free that often.

Now as for special problems, I'll leave that ball in your court.
Suggest a project when you want to (post to
[email-masked]) or express interest in one of the
projects that pops up on the group.

Gotta go... will be away this weekend so I won't be able
to respond to mail... sorry bout that.

Cheers,

Chris