[Elecraft] TX IMD

[Dave Hachadorian]

There is something that has been puzzling me for the last 17
years.

In November of 1991, QST reviewed the Yaesu FT-990, which
used a 13.8 vdc PA. Worst case measured 3rd order IMD
was -38 dB, 5th order was -47 dB. This measurement was at
100 watts output. The review is available on ARRL's
members-only web site.

ARRL had this comment, "It's refreshing to see that it's
possible to make a 100-W MF/HF radio with low voltage finals
AND such low-distortion transmitter performance".

As far as I know, no ham 13.8 volt radio has even come close
to this TX IMD performance ever since.  Looking at the 990
PA, there's a 2sc2166 predriver, a pair of 2sc3133
drivers, and a pair of 2sc2879 finals, all npn transistors,
nothing exotic.

So what was Yaesu's secret, and why hasn't anyone else even
come close?

Dave Hachadorian, K6LL
Yuma, AZ

























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