I re-ran the IMD tests with another PS and put 30 db more attenuation in front 
of the spectrum analyzer and the K3 now looks good above 65 watts.  -30 db IP3 
at 100 watts, in fact.
Sorry.
But it's still cleanest down in the 30 watt range.
Rick  K2XT



> From: rstea...@hotmail.com
> To: elecraft@mailman.qth.net
> Date: Tue, 1 Sep 2015 15:18:05 +0000
> Subject: Re: [Elecraft] K3S IMD Questions
> 
> I have been playing with a Flex 6300 here in my shack recently.  I consider 
> it a great piece of test equipment for analyzing signals in the shack as well 
> as on the air.  It does everything and more, as a spectrum analyzer, that my 
> old HP141 analog setup did, except it doesn't have a tracking generator.  
> My measurements are not completed and I am still experimenting, but here is 
> what I've done so far.  Phase noise, cw transmitted bandwidth, and 2 tone IMD 
> tests.  My two rigs are a K3/100 and an FT100D (how good, and how bad can you 
> get!)
> Using a Flex 6300 as a spectrum analyzer, I fed a greatly attenuated signal 
> into it, keeping the level just under 0 dbm, and assuming it is not 
> generating imd of its own, but I haven't quantified that yet.
> Phase noise tests - I was interested in seeing if it could display the 
> RELATIVE benefit of the new synthesizer on my K3, looking at phase noise. 
> Here are PRELIMINARY RELATIVE results, without numbers, in order of phase 
> noise level at 2 khz separation:An 8640B signal generator (known to have low 
> phase noise)The K3 with original synthesizerThe FT100 After I install the new 
> synthesizer I hope to be able to compare it to the original one.
> I verified the FFT spectrum analyzer (Flex 6300) can give an instant view of 
> transmitted bandwith of the cw signal sending fast dots. MUCH easier and 
> better than the old analog HP spectrum analyzer which had to sweep extremely 
> slowly across the band with a narrow filter.  With this setup you hold the 
> key closed, and hit the control-print screen buttons on the keyboard and you 
> have a beautiful picture !  Ain't technology great?
> 2-tone IMD measurements -The two tone test of the K3 showed something 
> interesting, since it has both 10 watt and a 100 watt PAs installed.  
> Starting with low power and cranking up the power control, you notice, of 
> course, that the ten watt PA has worse IMD just before the big PA kicks in, 
> in the 11-12 watt range.  Then it is very clean (approximately -40 db for 
> third order) at its best, and ok in the 30 watt range (where it would be set 
> to run my 8877 amp) but then gets quite ugly above 65 watts.  And I mean in 
> the -20 db range at 100 watts.  IF it was overloading the spectrum analyzer 
> these tests would be invalid, so I need to verify that.  As I said these 
> tests are preliminary.  I need a few more hours.
> 
> In my humble opinion, running at full power, 100 watts barefoot, my K3 would 
> be transmitting an unacceptably sloppy signal.  Keeping it in the 65 watt 
> range or under, or driving an amp would be better, provided your amp is 
> clean.  My 8877 amp is VERY clean.  I don't know about a solid state amp.  
> Some of the ugliest signals I have seen on the bands with the Flex panadapter 
> in very limited observations have come from Expert 1500 watt amps (2 
> examples).  The very best was an Anan 100 with a Ten Tec 1500 watt tube amp.  
> The waterfall was a brick wall - NOTHING whatsoever outside the 3 khz 
> bandwidth.
> Rick  K2XT
> 
> 
> 
> 
>                                         
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