Jim,
But Joe, you are fixating on a single specification, which is only
one part of what establishes the cleanliness of a radio. On CW and
FSK, there is the keying waveform, and on all modes there is phase
noise.
IMD is not an issue with CW or FSK (or JT65/JT9 for that matter) - they
are modes designed to work with saturated (class C) amplifiers. IMD is
a real issue with SSB when you separate out all the other junk caused
by bad ALC, excess IF gain and excess *audio* processing.
The K3 can be 4 to 6 dB *cleaner* than it already is if the proper
approach were taken in the KPA3. Since I don't use an amplifier, I
want the cleanest "exciter power level" possible and it is annoying
that given all the other attention to detail, the K3 has a dirty PA
(IMD comparable to the IC-706mkIIg on my test bench) simply to make
it compatible with a battery pack.
Six months ago, when I began doing my own measurements with a
P3/SVGA, you insisted that the IMD in a K3 would make a mess of
PSK31, so I measured PSK31 signals. They are in the set of P3
measurements I have posted here several times, and they clearly show
that you were wrong! :)
Your PSK31 "measurements" are clearly not believable. Look at the
IMD values in most PSK software when the K3 is run at more than 30
to 40 watts *average* power output. You will see the PSK IMD rise
significantly because the KPA3 is going into compression. If you
measure at 100W *instantaneous* peaks (using an oscilloscope and
looking for 70.7 Volts peak RF across 50 Ohms), the average power
in a PSK31 signal (e.g. measured on the K3 Wattmeter or a Bird 43)
will be around 30 Watts then the IMD of the KPA3 (and the rest of
the signal chain) will be acceptable. If you press the K3 to 100
W *average* output in PSK31 the PA will saturate, you will cause
about 4 dB of compression (peak clipping) of the PSK waveform and
PSK IMD will be around -15 dB or worse.
Non-linearities (compression) destroy BPSK and QPSK signals.
73,
... Joe, W4TV
On 2015-05-11 11:12 PM, Jim Brown wrote:
On Mon,5/11/2015 6:45 PM, Joe Subich, W4TV wrote:
The K3 may be cleaner than low end 12V/100W rigs like the Icom 706mkIIg
7000, 7100, Yaesu FT-450/991, etc. but it is certainly *not* as clean
as the other top of the line contest rigs like the Icom 7600/7800,
Yaesu 2000/5000, Kenwood 990, etc. For example, ARRL measured the K3
at -29/-43/-46/-51 dB vs. -32/-49/-52/-54 dB for the Icom 7800 and
-31/-46/-54/-57 dB for the TS-990. That makes the K3 3 to 6 dB *worse*
than other top of the line rigs at rated output.
But Joe, you are fixating on a single specification, which is only one
part of what establishes the cleanliness of a radio. On CW and FSK,
there is the keying waveform, and on all modes there is phase noise. The
K3 rise time for both modes is quite well controlled, so the keying
transients that excite IM in those other radios don't excite IM in the
K3. And phase noise in the K3, even before the new synth boards is close
to the best of any modern radio.
The occupied bandwidth measurements show the SUM of all these
mechanisms. I've been using pink noise for SSB spectrum measurements
because the signal excites IMD in a manner similar to what a voice
would, and I've made measurements with me talking into a live mic.
There's no significant difference between the live mic and the pink noise.
The FTDX5000 report to which I posted a link shows that the K3 and
FTDX5000 have almost the same occupied bandwidth on SSB, but the K3 has
10 dB of signal processing. AND -- my K3 is even narrower because I've
cut everything below about 400 Hz with TXEQ. If you missed the link,
it's on my website.
In many contests, I've got a CQ machine 8 miles from me with a 7600 and
a legal limit amp who regularly wipes out 5-10 kHz on CW, but K6XX, only
3 miles away with a K3 and ancient tube amps is only 700 Hz wide at -50
dBC. The 7600 and 7800 tested quite similarly in bandwidth tests by ARRL.
Six months ago, when I began doing my own measurements with a P3/SVGA,
you insisted that the IMD in a K3 would make a mess of PSK31, so I
measured PSK31 signals. They are in the set of P3 measurements I have
posted here several times, and they clearly show that you were wrong! :)
For those who missed the link, the measurements, as well as a
description of my test setup, are on my website. k9yc.com/publish.htm
73, Jim K9YC
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