On 7/9/2023 11:32 PM, dyno lab wrote:
However, a new K3s Retrofit RF power amplifier is coming on the market that
will resolve this problem and it may be seen in my W7YNC Bio at QRZ.com
Engineering is NOT defined as producing an ideal product, but one with
certain user objectives, one of which is operation from 13.8VDC, and in
a compact package that can be carried on an airplane to a DX operation.
The K3 solves the latter design objectives quite well; while it's IMD is
not wonderful at 100W, it's pretty good at the 25-50W level need to
drive most power amps, and the real enemy of two radios in close
proximity on the same band, phase noise, is spectacularly good. What
matters about IMD are clicks and splatter when the signal is loudest,
usually when it is driving a legal limit amp.
It's a byproduct of my work in the highest levels of pro audio, where I
learned not to make the lab measurements of a distortion, but to measure
the practical effects of it, clicks and splatter. And modern spectrum
analyzers, like the P3/SVGA and lots of SDRs with good software blow
away the lab gear for these measurements by at least two orders of
magnitude! The frequency resolution of my HP8590D is only 100 Hz,
compared to the P3 at a few Hz and the P3SVGA 10x better! Yes, the P3
can display only 80 dB of its 100 dB dynamic range on screen, but the
bodies are buried in the range of 40-70 dB down!
The K3 is a spectacularly good neighbor on CW, thanks to the carefully
shaped keying -- my neighbor K6XX and I, about 3 miles apart, can run
legal limit to serious antennas and work within 500 Hz of each other
when contesting. And thanks to the control of phase noise, our CQP team
could run K3s with KPA500s on the same band with in-line dipoles and
Yagis from 80-10M.
At home, I learned that could run two K3s and Ten Tec legal limit
3CX800A7 amps on the SAME BAND, 20M and above, within 60 kHz of each
other, feeding Yagis separated by 100 ft, colinear to each other, and
not know the other transmitter was there!
There is FAR more to life than measurements of IMD test signals! A FAR
better test of IMD is the measurement of the bandwidth of a signal using
spectrum analysis capable of very narrow resolution bandwidth, like the
P3 (a few Hz), or even better, the P3/SVGA (a few fractional Hz).
Download and study
http://k9yc.com/P3_Spectrum_Measurements.pdf
and
http://k9yc.com/TXNoise.pdf
The first link shows measurements of my K3, pre-upgraded synths, driving
a Ten Tec 425 (2 3CX800A7s), a KPA500, and another amp I sold as soon as
I realized how dirty it was compared to the others. The second link is
my analysis data ARRL Labs sent me in electronic form of their
measurements of more than a dozen rigs, plotting all on the same graph
making comparison jump out at you! It was motivated by complaints by
WRTC participants of trash competitors in the same group of sites were
generating with rigs like the FTDX1000.
BTW -- after I'd done the work for the first link, Warren Pratt, NR0V,
inventor of Pure Signal and long-time running partner of Rob Sherwood,
NC0B, demonstrated to me that the RX in the $900 ANAN transceiver could
display fractional Hz resolution with 120 dB dynamic range with his
software (for ANAN) running the radio. I bought one to use in my
measurement lab! I've never used it as a transceiver.
73, Jim K9YC
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