[Elecraft] FW: Testing IMD3 (dB) K3S (#10490)

[Jim Brown]

On 2/7/2020 4:00 PM, hb9cvq at hispeed.ch wrote:
> I think these IMD3 values are not very impressive. A power amp. would
> typically further degrade the overall results.

In practice, no, because the K3 and K3S IMD is significantly lower at 
the power levels needed to drive an amp. My 87As need 45-55W, my KPA1500 
30-50W, and KPA500 25-30W, in all cased depending on the band. IMD is 
also minimized by running the radio near the top of its design range 
13.8V nominal, 15V max).

> So K3S is rather good for CW but not really good as SSB preference? (I have
> now also a FTDX101MP)

When they were introduced, the K3 and K3S both pushed the state of the 
art for CW bandwidth with low phase noise and a carefully shaped keying 
waveform (that others took years to copy). My measurements of the TX 
bandwidth of my K3 and several other rigs I was able to borrow are here.

http://k9yc.com/P3_Spectrum_Measurements.pdf

It's also important to realize that IMD increases CW bandwidth too, 
because CW is actually 100% square wave amplitude modulation of the 
carrier. Compare slide #9 with #14 - 16, for example. Those little humps 
that look like sidebands are IMD, and are heard as clicks. Compare slide 
#17 (100W SSB) with those that follow. Pink noise is used as a test 
signal because it's spectrum and dynamics far more closely resemble 
speech that white noise.

73, Jim K9YC