Violating guidelines and replying inline.
On 5/25/2018 2:25 PM, Jim Brown wrote:
On 5/25/2018 1:43 PM, Wes Stewart wrote:
I have no idea what you are actually measuring but it certainly isn't IMD in
the classical sense.
I think I made it plain that I was measuring the "envelope" of keying
sidebands, usually described as "clicks." This envelope is due to a
combination of the shape of the keying waveform and IMD.
Actually, you said below, "I evaluate IMD blah blah..."
FWIW, I really don't care about IMD as a number. What I'm concerned with is
clicks, splatter, and phase noise from another station that's loud covering a
weaker station I want to work.
Since the numbers are more-or-less specified by Elecraft I'll go by them. I say
more-or-less because they don't actually have a firm specs.
While it might be "well known" that IMD decreases at lower power, it isn't
necessarily true.
Right -- it depends on the transmitter design and implementation. K6XX's work
shows that to be true of the K3, and my measurements (done on 20M as I recall)
confirmed it. I also recall that you noted increased IMD around 15W, which is
likely the result of the K3 firmware causing the power amp to be turned off
and the QRP output stage to be driving the load at it's full rated power.
Under that condition it is consistent with my (and K6XX's) observations that
IMD is often lower at reduced power output.
You recall incorrectly. First, I've never stated that and second, the HPA
engages at 12 W. I have however, stated in strong terms several times in this
and other forums that a K3 should never be operated above 10W on the LPA. I and
others have asked for a firmware change that would insure this.
What is really not well known is that in the K3(S) IMD is highly frequency
sensitive.
That's news to me.
Well even experts can learn something new now and again.
The 3rd order IMD in my K3S at 10W output varies 18 dB with respect to
frequency.
Again, the power amp is not engaged and you're running on the driver. But that
much variation also implies a problem. Have you sent the rig back to Elecraft?
Just four times. (Actually, three times and I changed the HPA once.)
Furthermore, my K3S on 10, 17, 20, 30 and 40-meters has higher IMD at 20W
than at 100W.
Interesting.
Yep. Which is why I state that I can't with reasonable confidence measure
KPA500 IMD.
Wes N7WS
73, Jim
Wes N7WS
On 5/24/2018 8:17 PM, Jim Brown wrote:
On 5/24/2018 7:30 PM, Wes Stewart wrote:
I haven't measured IMD on my KPA500 either since I don't own two generators
that are clean enough with the necessary power to do so.
I evaluate IMD by looking at keying sidebands of a long series of dits, as I
posted hear yesterday. Details of the measurement setup and method, and
lots of results, are here. http://k9yc.com/P3_Spectrum_Measurements.pdf
It's well known that IMD in the K3/K3S increases at rated output, and is a
lot lower at the levels needed to drive a power amp. It takes 25-30W to
drive the KPA500 to full power, and about twice that to drive my Ten Tec
Titans. The K3/K3S is pretty clean at these levels. The plots for the two
amps look almost exactly the same, and have the same shape as the K3 at
those drive levels.In other words, neither amp is increasing bandwidth. Note
that these measurements are of the envelope of peaks, so they are, in
essence, capturing clicks.
IMD also increases with low DC supply voltage. I've not done any disciplined
measurements to put numbers to it, but K6XX has. His data is in this pdf
slide show. http://k9yc.com/K6XXAmpTalk.pdf
73, Jim K9YC
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