>
>
>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.
good show
>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!
>
well put, George
- Rich..., 805.386.3734, www.vcnet.com/measures.
end
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