CW Bandwidth

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From: Marshall Emm (mgemm@mtechnologies.com)
Date: Sun Jun 01 1997 - 09:07:22 EDT


I get annoyed with published articles in which the author is either
sloppy or ignorant about matters relating to CW operation-- e.g
confusing the mode with the code, or calling an A1A signal
"interrupted continuous wave"-- but I have my own areas of ignorance
and hope someone on the list can clear something up for me.

When I started to "learn radio" almost 30 years ago, CW was
defined as a "continuous wave" having a single frequency,
turned on and off to provide telegraphic content.

The CW signal, like an AM carrier, was specifically described as a
"point frequency" having ZERO (or "infinitely narrow") bandwidth.

When I was studying for my US license I had to learn that a CW signal
has a bandwidth in Hz equal to 5 times the keying rate in words
per minute. There's at least one exam question on that.

A quick check of the ARRL Handbook indicates that a CW signal will
always have key-clicks and/or (?) switching transients, and therefore
will occupy bandwidth. But...

A) surely this is a factor of the state of the art in equipment
design (some rigs are clickier than others, and there is an
apparently unspecified point at which key clicks become a reportable
fault), and

B) surely, given the above, to presume a constant rate of
bandwidth creep as a factor of speed in wpm must be pretty arbitrary.

By the way, they never said whether those were "PARIS" wpm or "CODEX"
wpm, which indicates a secondary layer of arbitrariness [g].

I can understand that a pure A1A transmission is not practically
achievable (just as I understand that you can't really fit an
infinite number of CW signals into a single Hz), but it does seem odd
to me that we would muddy the waters by apparently assigning a
notional bandwidth in such arbitrary fashion! And how could such a
thing become enshrined in the technical doctrine as reflected
in the question banks?

Maybe it's time to see about some medication. Maybe this is like
arguing about how many angels can dance on the head of a pin, but
then again maybe we can find out if we get down there and boogy with
them [g].

 
73
Marshall Emm
AA0XI/VK5FN
aa0xi@mtechnologies.com
http://www.mtechnologies.com/mthome


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