Scroll down to the bottom of this and you will see it was me :-)
I have made hundreds of IMD measurements on both my K3 and K3S using the
built-in two-tone generator and an SDR-IQ/SpectraVue as a spectrum analyzer. I
have a string of power attenuators followed by a step attenuator for calibration
purposes. Within its linear range the SDR-IQ is remarkably good. This is a
laborious process, sped up a little with the K3 utility and saved instrument
states in SpectraVue. One nice thing about this setup is that I can actually
record the spectrum display and play it back later for analysis just as if it
was live. A guy smarter than I could probably automate this; I put the numbers
in an Excel spreadsheet and let do the charting.
What you can find doing this is that the IMD is sensitive not only to power and
voltage but to frequency. Pick the right frequency and IMD can be -40 dBc, pick
the wrong one and it's -20 dBc; same radio, same supply voltage and output power.
Wes N7WS
On 12/13/2018 3:50 PM, Bob McGraw K4TAX wrote:
Someone suggested performing 2 tone tests. Seems reasonable.
I tried that with my K3S into a dummy load and an a RF sample fed to my RSP1
receiver using HDSDR software. I find that it does indeed display the IMD
products from the 2 tones. I now need to study the results a bit more to
evaluate the test.
{Oh, don't forget to set 2 TONE to OFF mode or you'll get a surprise when you
jump into that SSB rag chew group. The comments won't be very kind.}
73
Bob, K4TAX
On 12/13/2018 1:03 PM, [email protected] wrote:
It would be nice to know what conditions caused this FET failure. Is there
an easy way to know when this failure occurs other than getting crappy
audio reports?
John KK9A
Peter Dougherty (W2IRT) wrote:
This happened to me at the start of CQWW-SSB in October. My K3s is finally
enroute back home after a 6 week stay in the Elecraft Repair Department
with a blown FET in the HPA, cause unknown. And I know I've been told I'm
not the only one to suffer this failure, and it sounds like this is now a
known issue.
Does anybody have an idea as to what could be causing these FETs to fail,
or steps to consider to lessen the chances of it happening? I can't speak
for anybody else, but I baby the heck out of my gear and was shocked to
discover it failed, when feeding directly into a KPA-1500.
----------------------------------------------------
Regards,
Peter Dougherty, W2IRT
-----Original Message-----
From: elecraft-bounces at mailman.qth.net [mailto:elecraft-bounces at
mailman.qth.net] On Behalf Of Wes Stewart
Sent: Wednesday, December 12, 2018 4:55 PM
To: elecraft at mailman.qth.net
Subject: Re: [Elecraft] K3 Suddenly Putting Out Only 25 watts at 100 watts
indicated
If you have another receiver, run a two-test and listen to the K3 output in a
narrow BW. Ideally, the two tones will be considerably stronger than the
first
pair of sidebands.
I suspect they won't be, you'll have a lot more than two and you have a blown
FET in the HPA.
Wes N7WS
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