[CQ-Contest] CW Band width

Tony Field field at nucleus.com
Mon Feb 26 12:57:42 EST 2001

----- Original Message -----
From: "Tom Rauch" <w8ji at akorn.net>

 > Rise and fall times are only a small part of the bandwidth issue
 > Tony. Synthesizer settling and bounce can be a major player.

If a modern synthesizer is used to key the radio and the radio is not
running in full QSK mode (or if separate synthesizers are used for RX and
TX), I suspect that the only time settling and bounce should be (possibly)
important is for the first cw symbol.  Subsequent symbols should be stable
as far as settling and bounce is concerned.  Thus, I suspect that the rise
time is the biggest single contributor to the "key click" syndrome (the
'apparent' band width).  If the synthesizer has considerable lock range or
jitter, then this  could be a reasonable contribution to the close-in
carrier band width.  It would be interesting to see the band width plot for
a "traditional" (non synthesized) radio and a current production synthesized

It would be useful for some authority to publish a good article on band
width that covers cw, ssb, rtty, and psk. I suspect that most of us have a
rather vague notion (mostly associated with crystal filter widths) of what
bandwidth really is.  I suggested that the ARRL publish such an article -
however I have received no reply.

 > PSK people try to sell it based on how narrow the mode is, and yet
 > it has one of the poorest dynamics of any system used! You
 > should see how the PSK people whine about QRM from other PSK
 > signals when the strengths are 30-40dB different.

I must apologize for showing the image - the psk content was only  there
because of the article from which the image was copied.  The real intent was
to show that CW signals are not as narrow as we suspect.  If someone has
more useful band width info for CW please let us know.  The fact that psk31
is generally narrower than CW is immaterial.

tony (ve6yp)

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