[Amps] Re: [Amps] Re: [Amps] Re: [Amps] BirdŽ 43 Ma nual

[Tom Rauch]

> 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