From: utzoo!decvax!cca!Stephany.WBST@PARC-MAXC@sri-unix
Newsgroups: net.ham-radio
Title: Re: Thoughts on CW
Article-I.D.: sri-unix.4472
Posted: Mon Nov 29 09:01:33 1982
Received: Tue Nov 30 02:24:27 1982

The bandwidth of a CW signal is 4 times the words per minute (5 letters/word
not 4 letters/word as in Canada and England).  As the information rate is
increased the bandwidth goes up  ....  a law of physics and  not a thing that can
be eliminated.  The confussion in these types of arguments is the fact that you
mix the time and frequency domain.    In the frequency domain there are only
sidebands and carriers that never change in time.  In the time domain there are
only carriers that change in amplitude. The components in the frequency domain
always add up to what you get in the time domain (fourier transform).  In the
case of CW the unvarying components in the frequency domain add up to a
signal in the time domain that goes on and off. The components in the frequency
domain do not go on and off when keyed.

The frequency domain is what you get when you tune across a signal with a
receiver of bandwidth much much  less than the signal bandwidth.  The time
domain is what you get when you tune across a signal with a bandwidth much
wider than the signal bandwidth.  In reality we are always between the two.
Usually you set your bandwidth to be just a little bigger than the signal so the
output is in the time domain but not so much in the time domain that you get a
signal you don't want.

If a dit becomes a microsecond then the bandwidth is about two megahertz or a
little more and you occupy two megahertz of spectrum.  The FCC doesn't like
that although the Germans did just this during WW2 in sending to their subs.
They sent CW in a burst, recorded it and played it back at a low speed so the
operator could copy it.

The faster you switch on and off the wider the bandwidth.  If you restrict the
band width you lose information. In other words Shannon's formula:

   Signal bit rate/Bandwidth = log(base 2)  (signal/noise +1)

If you send more information you need more power or more bandwidth.  This is
a fundamental limit of nature for which there is, at present, no way of getting
around.

				Joe   N2XS