As some have indicated the TS850 at full ouput has a very poor IMD
supression. I have heard several of these radios on the Air cranked up to
200 watts and the splatter is horrendous. However having said that,, i will
say that the TS850 cranked down to drive most amplifiers is one of the
cleaner radios out there.
There seems to be considerable IMD level variation between manufacturers
using the same devices, in particularl the 2sc2879. Why this is so i have
yet to analyse. The TS50, FT990 and TS850 all use 2sc2879 transistors.
However the 2 tone IMD figures combined with 5 the 20 khz away numbers show
wide variation. I suspect this has a lot do to with biasing and poor ALC
design, see SM5BSZ. The FT990 using 2sc2879 is capable of 200 watts output
as well, however this radio has a 2 tone IMD suppression of -36 db pep 3rd
order, just dont activate the ALC. Very good for a 12 volt radio.
Its becoming a battle to find a radio that has a low IMD final amp that
does not splatter. Besides the Yaesu Class A feature, most radios are about
the same, poor to close to horrible. I was shocked to read the review in
QST of the Yaesu FT857D, a final figure of -15 db below one of two tones.
Not a word from the reviewer about such a horrible radio. With a radios
like that being sold i think i can start drawing a few mills of gird
current on the 4-1000 tetrode if most new l radios are going to be of that
standard!
Craig
VK3HE
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