RadioBanter - View Single Post - W2DU's Reflections III is now available from CQ Communication...

Owen Duffy · May 28th 10, 01:08 AM posted to rec.radio.amateur.antenna

Keith Dysart wrote in news:7974e65c-6e3a-442b-
:

You left Class A out of the list. Does this mean that Rp is the source
resistance for a Class A amplifier?

Keith,

Assertions have been made about the Thevenin equivalent source impedance
(Zs) of an RF PA. In the discussions over the years, some people have
imposed some qualifications (eg classes, tuned / untuned etc).

Zs can be measured by a number of methods. It is interesting to note that
in many of the discussions on the 'net on this topic, more focus is given
to dismissing the experiment design for experiments that produce
unfavourable results to some, than questioning the proposition that Zs is
50+j0 or thereabouts.

Whilst Walt has documented a quite rigourous experiment, and it produced
a favourable outcome, it is my view that that in itself is not proof of
the proposition.

Whilst one favourable experiment cannot proove the proposition correct,
just one valid experiment can prove the proposition to be not generally
true. No doubt the reason for the focus on proving experiments invalid.

If you give some thought to what you could use Zs for, then every valid
experiment that is designed around that application must produce a
favourable outcome if Zs is as proposed. If they don't, then the value
assumed for Zs must be wrong.

I posted a simple test earlier that in my experience does not support the
proposition that typical ham HF transmitters have Zs=50+j0 or close to
it. The test is documented so that individuals can try it and make their
own mind up. Some might get favourable results on limited trials... but
in my view, that is outweighed by unfavourable results from valid
experiments.

Owen