[Elecraft] Key Clicks

[Earl W Cunningham]

Keith, W8GX wrote:

"How does one go about measuring the CW bandwith of a transmitter and is
this information available in the ARRL reviews or anyplace else?"
========== 
Someday perhaps the ARRL will publish CW bandwidth figures in their
reviews.  They'll probably use a lab spectrum analyzer to determine CW
bandwidth as X dB down at Y Hz from center frequency.  Many CW contesters
will read those figures with great interest because key clicks are a
major problem today, especially during CW contests.

I don't have a spectrum analyzer, so here's the way I do it:

1) I set up the transmitter under test to send a string of dits at about
30 wpm into a dummy load.

2) I set up a receiver with a narrow CW filter (250 Hz or less) to
monitor the test transmitter.  The steeper the receiver's filter skirts,
the better.

3) I adjust the power output of the test transmitter and/or the
receiver's antenna attenuator so that the received signal is S-9 (about
100 uV is S-9 on most of today's radios when their preamp is turned off).

4) While sending a continuous string of dits from the test transmitter,
tune the receiver away from the signal's center frequency until it is
just outside of the receiver's passband.  All that you will hear now are
"clicks".

5) Continue tuning away from the signal's center frequency.  The clicks
will gradually diminish in strength until they can no longer be heard. 
Call the point where they can no longer be heard "freq A".

6) Repeat steps 4) and 5) on the opposite side of the center frequency,
but call the second measurement "freq B".

7) The difference between freq A and freq B is the bandwidth of the CW
signal.

Not very scientific, but that's the way I do it and it agrees closely
with others who have measured CW bandwidths including one of the gurus on
the subject, W8JI.

73, de Earl, K6SE