[AMPS] Conjugate Matching and Efficiency

[Tom Rauch]

> I was cruising through my 1987 ARRL handbook the other day (yes, I have a
> newer one, but I am more familiar with the old one).  In the PA section,
> it does the VERY thing Tom says you can't do.  It talks about efficiency
> based on the resistance of the source.  It goes inside the source model
> and acts like there is a dissipative resistance inside.  They even show
> this nice graph of efficiency vs. match vs. power transfer to buttress
> this "fact."

It isn't if I say we can or can't do it that is important. 

What is important is the MODEL says we can't use the model that 
way!

Say we have a transmission line coming out of a wall and we don't 
know what is on the other end. We have a nearly lossless 
matching network we place at that point, and adjust it for maximum 
available power into a load.

That satisfies the Maximum Power Transfer Theorem, and creates 
a conjugate match. What is the power loss in whatever is behind 
the wall?

The ARRL Handbook says it is 50%. Truthfully, it can be nearly 
100% if the source is a class D amplifier, or near zero percent if it 
is a class A amplifier with low drive and high quiescent current. We 
don't know a thing about what happens on the other side of the 
wall, and don't care. The model can only tells us what to do to have 
maximum available power in the load.

The only thing the Handbook proved is someone doesn't 
understand why we use models.
73, Tom W8JI
W8JI@contesting.com 

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