Hi,
It was written....
> >>It is only true if the amplifier is tuned up at 250w. If the amplifier
> >>was tuned up at 1000w, and then the drive was reduced to 1/4, there would
> >>be less circulating current through the contacts with reduced drive. .
> >
> >Don't I recall that you (and maybe others) have indicated that this is the
> >proper way to tune for best IMD --- set up at full power and then reduce
> >the drive?
> >
> Carl Heuther and some others approve tune-up at full smoke - followed by
> a small increase in loading. I doubt that increasing loading a tad
> makes a noticable improvement.
I also think this is a good way, so long as "full smoke" is
equivalent to "full smoke with good linearity." I actually played
with the loading while watching the 3d and 5th order products on my
4cx1600b amp. (Two-tone test... I know, I know!) While loading a
bit heavier didn't make a significant improvement in linearity, it
was a move in a good direction. That is, if I DECREASED the loading
a bit, then 3d and 5th order nasties INCREASED measurably. So "full
smoke and a small increase in loading" was a conservative recipe for
tuning.
> The major source of feculence is
> undoubtedly solid-state radios - not amplifiers. For example, 3-500Zs
> are typically -40db, while radios are in the low to mid-30s range.
Yep. My 4cx1600b ran minus 35-38 db using two RF tones from two
(CW) exciters and a carefully balanced combiner. Using two audio
tones into any of my exciters gave just over -30db. That's when I
realized that a two-tone test using two audio tones into a "modern,
store-bought" transceiver wasn't an adequate way to test the
linearity of an RF amplifier!
73,
George T. Daughters, K6GT
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