> Thanks for jumping in Tom. Whether all the power is absorbed in the
> PA does not matter to me as long as some of it is. My point is that
> my transceiver which is drawing 20-amps DC at 13.8 VDC is dissipating
> power somewhere in the radio.
Conservation of energy makes that true. The radio has to be
outputting 20 amperes times 13.8 volts worth of energy in some
fashion...either by light, RF, heat, mechanical energy or something.
My point is that for many combinations of load impedance, PA
current is REDUCED which generally means heating is reduced.
Those are the load combinations that increase voltage on the PA.
This is a primary reason PA's arc tuning caps or bandswitches
when underloaded or if the load faults at high power. Either current
becomes excessive (which potentially overdissipates the tube or
transistor) or voltage becomes excessive which potentially reduces
dissipation but increases voltage (which potentially causes an "arc"
or other voltage related component failure).
If I take my Omni Six and attach no
> transmission line whatsoever or if I attach an essentially lossless
> length of unterminated line, where is the power being dissipated?
Depends. If the line is the correct range of lengths and has no flaws
like instability there will be LESS power dissipated than when the
PA is properly terminated. Only voltage will increase, which
hopefully will not punch through the junctions of the output device
or cause it to break down.
There also can be more power dissipated if the line is within a
certain range of lengths.
> Let's assume for the moment that the radio cannot attain full power
> under this condition. Where then is *any* power attained being
> dissipated?
Any increase in dissipation is mostly in the PA section and mostly
in the output device, IF power input does not drop more rapidly than
load power reduction decreases. But there are almost always
phase angles of the reflected signal that will cause input power to
drop more rapidly than load power drops.
>
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>
73, Tom W8JI
W8JI@contesting.com
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