[Elecraft] K3 Suddenly Putting Out Only 25 watts at 100 watts indicated

[Wes Stewart]

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, john at kk9a.com 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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>
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