I was not surprised to see a comment about the Tx IMDs in the QST article.
One of the first problems I encountered with my new K3s/10 was poor Tx IMD
performance. What I observed was flat topping that started at about 5W, and
progressively got worse as the power was increased. The distortion was so
bad at 10W, the envelope looked more like a squarewave than a two tone
signal, and the 3rd order products were down only -18 dBc. After several
months of working with Wayne, Rene, and the designer of the KLPA3A
amplifier, replacing the KLPA3A three times, and sending the radio to the
factory, the problem was reduced, but I still don't see better than -28 dBc
at 10W out. Not wanting to send the radio in to the factory a second time, I
decided to just live with the performance.

The transmit signal generation in the K3s is a complex process based around
the internal computer. Signal quality is affected by ALC, transmit power
level, configuration settings, and the transmit power CAL, however, from all
of the testing that I did, the signal going into the KLPA3A was very clean
(-40 dBc). It is also important to note that Elecraft's approach to
distortion management includes spreading the energy in the distortion out
spectrally by the use of pre-distortion. This results in 5th, 7th, 9th,...
order products being higher compared to some radios, as noted in the QST

The QST article indicated that both the KLPA3A and the KPA3A have been
modified to address the Tx IMD problem. I am hopeful that at some point
Elecraft will offer some info/options that will allow us to bring the
unmodified radios up to the performance shown in the QST article

Bill  N0CU

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