On Feb 25, 2005, at 12:39 PM, VK3HE Craig wrote:
> 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.
Craig -- What sort of IMD results when a TS-850 is operated from 16vdc
and the power is adjusted to 160w?
> However having said that,, i will
> say that the TS850 cranked down to drive most amplifiers is one of
> the
> cleaner radios out there.
Agreed, and the Rx audio has remarkably low distortion as well.
>
>
> 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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Richard L. Measures, AG6K, 805.386.3734. www.somis.org
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