On 9/26/2018 8:48 PM, Jim Thomson wrote:
K9YC can chime in
Actually, I'm citing K6XX, an EE who works for Elecraft and has been
part of the team working on their power amps. This was news to me too.
Bob is my neighbor (about five miles), and we're both contesters. This
issue is not unique to solid state amps. When I moved here from Chicago
12 years ago, he made sure that I knew the importance of tuning my amps
(then a pair of Ten Tec Titan 425s). At the time, he was also running
tube amps; now he's running one tube amp and one KPA1500. I'm currently
running 87As.
While contesting at legal limit, Bob and I can work 500 Hz apart on CW
and hear each other as nothing more than a strong signal.
Bob's take on this is in a talk he gave to our contesting club in 2013,
to which I added material on audio and P3 spectrum plots of both his
signal and some dirty ones. The slides are here.
http://k9yc.com/K6XXAmpTalk.pdf
Remember that CW is 100% amplitude modulation by a rectangular wave,
which consists of very strong AF harmonics. Those harmonics create IMD,
and can be clearly seen on spectrum plots. The combination of AF
harmonics and the IMD products are heard as clicks.
The best modern transceivers carefully shape the keying waveform to
minimize the harmonics, and thus the clicks. The Elecraft K3 is the
first rig that I'm aware of that did this, and several SDRs (Flex, Anan)
have followed suit. The early Flex rigs were pretty nasty, including the
first 6500/6700 that ARRL tested. Soon after, this was greatly improved
with new firmware that implemented the shaped keying waveform.
The worst rigs for clicks Yaesu, ICOM, pay little or no attention to
this, and even give the user a control to decrease the rise/fall time,
which increases the clicks. My own measurements of several rigs are in
this file.
http://k9yc.com/FTDX5000_Report.pdf
73, Jim K9YC
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