On Tue, 26 Apr 2011 14:37:58 -0700 (PDT), "Sal M. Onella"
wrote:

Thanks Richard. Intuition is that the Zs is near 50 ohms for as many
frequencies as the designer can manage. I am on record (including in
this group) of letting intuition lead me down the path to ruin.

Well, if you miss the path, you are certain to be reminded where it
is.

I get from you that there's a presupposition that I know the source
impedance or can easily establish it. Hm-m-m ... not so.

It is printed in the specifications. There are other ways to derive
it, of course, and they would merely confirm that number.

One big
problem I see is the need to try to measure power delivered in a
non-50-ohm system with my existing instruments that depend on a 50-ohm
system. I don't have a nominal 75-ohm power meter. Won't putting a
50-ohm meter into a 75-ohm circuit not only read wrong but introduce
reflection losses, too?

It is easier to measure voltage and current and use your calculator.
Now having said that, measuring voltage and current is damned hard at
HF. It is achievable with care, but now we are back into your same
question with many hands pointing at that path to ruin.

As both are difficult (power or voltage times current), you could
trust authority (which confirms what is intuitive), or you could
listen to argument (which at the distance of time and recall becomes
murky and opaque).

I think I'd need a collection of non-inductive load resistors and an
accurate rf ammeter. I'd need to connect them and calculate power at
a few points in every band.

Bravo! This reduces complexity because RF Power resistors of high
accuracy and bandwidth are commercially available. You will need to
practice your skill at mounting to a heat sink, however (another
non-trivial achievement).

Maybe the papers that Cecil cited for me will fill in the gaps or
suggest other approaches.

Walt and I have been corresponding over these matters just these past
two weeks. Skimming that content will once again confirm intuition.

73's
Richard Clark, KB7QHC