[Elecraft] High Tx IMD with new K3s/10

[Vic Rosenthal]

Not normal. Make sure the power supply voltage is stable and do the testing at 13.8v.

Vic 4X6GP

> On 3 May 2016, at 5:10 AM, Bill Leonard N0CU <billincolo73 at gmail.com> wrote:
> 
> I recently got a new K3s/10 built up and running. This week I ran some tests
> to get familiar with it and one test that surprised me was the high Tx IMD
> levels. I first noticed that the two tone waveform on a Tek o'scope showed
> flat topping starting at about 4.5 W. As the power level was increased the
> flat topping got worse. I checked the spectrum with my HP spectrum analyzer
> (on 14 MHz) and measured the following 3rd order IMD levels feeding a 1.1
> SWR:
> 
> 1 W: -36 dBc
> 4 W: -31 dBc
> 4.5 W: -33 dBc
> 6 W: -34 dBc
> 8 W: -25 dBc
> 10 W: -21 dBc
> 
> It was interesting that as the power was increased from 4.5 to 6 watts, the
> increased distortion didn't show up in the 3 rd order IMD, but rather the 5
> th and higher order products.
> Since I am new to Elecraft radios, I don't know if this behavior is expected
> or if there is something in my transmitter that needs to be checked out.
> I have built up a number of amps over the years and I am used to seeing flat
> topping start at, or a little below the maximum CW output power. My K3s puts
> out about 12 W max, so I was expecting the flat topping to start at about 11
> W.
> 
> Bill  N0CU
> 
> 
> 
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