Here's a pdf file collecting a lot of measurements I've made on the rigs
and amps I could easily get to measure.
http://k9yc.com/P3_Spectrum_Measurements.pdf
Remember that what we call CW is really 100% amplitude modulation of a
carrier by a rectangular wave. The rise and fall time have an infinite
spectrum, and the components excite intermod. Slide 8 is a steady
carrier with no keying. The sidebands at -70dBC are 60 Hz hum. Slide 11
is the same for an FTDX5000.
Slide 14 and many that follow are a series of dits at about 30 wpm. The
stuff below about 55 dB is IMD.
Slide 63 shows an amp that is adding IMD to a CW signal. Yes, the
sidebands are clicks. Slides 70-72 compare that amp to the Titan and the
KPA500 at their rated power.
On all of these rigs and amps, the differences are more than -40dBC.
That matters when the broad signal is very strong and the bands are
full. Like in a contest. :) I see lots of signals that are 20-30 dB
over S9, so their -50 dBC sidebands can wipe out a lot of signals I want
to work. And when one of these broad radios shows up next to my running
frequency, either he has to more or I do, because I can't hear half the
guys calling me.
The K3 keying is carefully shaped to provide clear keying at QRQ (up to
100 wpm). If I remember correctly, they're using a raised cosine
function to shape it. Isn't DSP wonderful? Last I've heard, the better
(later) firmware for some SDR radios is doing the same thing or
something similar.
Most other rigs give the user a menu setting that allows them to vary
rise and fall time; clicks increase with faster rise and fall times.
Below about 35 wpm, bandwidth is independent of keying speed and depends
only on the keying waveform; above that speed, information theory takes
over, and the higher speed causes bandwidth to increase. I don't work
faster than about 35 wpm myself, but some of the QRQ guys on 40M are
running WAY up there, mostly with keyboards, I think.
Not all of the broadness is clicks -- on the worst radios, some of the
really broad stuff is phase noise. That's the "whooshing" noise that we
hear corresponding to keying. BTW -- that Mark V Field had been "fixed."
K6XX has a big station about 3 miles from me on top of the ridge that I
have get over to get to EU. We both run K3s and tube amps. Because we
keep our signals as clean as possible, we can work 500 Hz apart on CW,
often not knowing the other is there.
73, Jim K9YC
On Fri,12/30/2016 8:34 PM, Jim Thomson wrote:
Date: Thu, 29 Dec 2016 01:27:49 -0800
From: Jim Brown <jim@audiosystemsgroup.com>
To: amps@contesting.com
Subject: Re: [Amps] FCC Denies Expert Linears' Request for Waiver of
15 dBRule
The IMD from this amp is significantly higher than my "good" amps, so
I'll eventually replace it, because I can't use it for contesting
(because the IMD makes it broad on CW). The Titan remains my contesting
amp, clean as the K3 that drives it at legal limit. But the SPE gives me
3 dB more than my KPA500 on 6M (and instant on at HF), which is why it's
on my operating desk. :)
Glen says the 1.3K he bought is close to 14-15 dB gain, but that the
vendor offered to tell him how to get the additional available gain. It
would, indeed, be nice if SPE used the additional gain to reduce IMD.
But the DXpeditioners love the 1.3K-FA -- it's light weight (thanks to
an SMPS), very close to legal limit. And when you're DX in the middle of
nowhere, you don't have neighbors who care if you're a bit broad. :)
73, Jim K9YC
## Im trying to wrap my head around poor IMD vs being broad on CW mode.
Im assuming a clean CW signal from the xcvr.... driving an amp with mediocre
IMD. Exactly what effect are you seeing. Does it sound like key clicks.
How much broader are you talking about, several hundred hz or what.
Jim VE7RF
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