[CQ-Contest] Band edges?

Tony Field field at nucleus.com
Sun Dec 17 08:57:06 EST 2000

From: "Barry Kutner" <w2up at mindspring.com>
> "operating out of band" during the CQWW CW contest. My
> frequency is listed as 21000.46 +/- 0.03 KHz. In the Remarks area,
> W3FAF wrote, "By FCC definitions your sigs were out of band -
> carrier below 21.000 MHz or CW bandwidth is too wide."

Possibly it is necessary to acquire a copy of the "FCC definitions".  Such
"definitions" are probably designed to account for a "worst case"
possiblility and not necessarily reflect upon a true measurement on an
individual signal.

> A CW signal 400+ Hz wide?!
> I was curious, and went to the ARRL Handbook. According to it,
> there is a linear relationship between bandwidth and CW speed.
> There is an example, stating a 60 WPM CW signal has a
> bandwidth of 150 Hz. As I was sending about 32-34 WPM, my
> bandwidth was about 80 Hz.

The occupied band width of the cw signal is related to speed and the keying
characteristics of the transmitter.  A transmitter with a steep rise time
for the cw symbol will be wider than one with a soft rise time.  The steeper
rise time results in key clicks - which is tantamount to wider band width.
This can be displayed on a spectrum analyzer. It may be that the FCC
definition assumes extremely hard keying characteristics.

This is also implied in the technical review of the IC756PRO when the ARRL
lab boys discuss the "keying artefacts" of the dsp processing and  concluded
that soft transmitter keying resulted in the absence of key clicks and the
hard keying displayed the "keying artefacts".

It would be nice if the ARRL techy folks could properly analyze the cw
signal width and report this in a good article in QST.

tony field
field at nucleus.com
ve6yp at rac.ca

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