On Sun, 20 Jul 2003 10:50:35 -0000, "David Robbins"
wrote:


Actually, several people (W8JI among them) have measured the output
impedance of common amateur linear amplifiers by at least a couple of
methods. The most credible measurements show, interestingly, a value
very close to 50 ohms when the amplifier is adjusted for normal
operation.

but is that a real resistive 50 ohms, or a dissipationless 50 ohms
non-resistive? or could it be a virtual 50 ohms hiding some other fake
steady state value?

What would make it real for you?

you can't read it when you connect an ohm meter to the
output connector, so how can it be a resistance?

You can't read a 50 Ohm resistor with an Ohmmeter through a 0.1 µF
capacitor either, would you hold one while you pour a KW at 10M to the
series pair?

or is it really a complex
impedance that can be ignored when you calculate the output power?

I used real loads. I can repeat this with reactive ones, but it will
only shift the curve of data.

but then
again it might be due to internal reflections making it an infinite sum of
many other factors?

That is the entire point and expressly demonstrated between the
mismatched plane of the source and the mismatched plane of the load.

maybe we have to learn how to conjugate our impedances
before we can have a decent discussion about it?

Care to give an example?

but what if its only a
matching system to free space impedance? when there are reflections does it
reflect or absorb? who started this topic anyway????


Hi David,

What if? What is reflecting? In this case BOTH the source AND the
load. If you wish, we can jimmy up the load to present 377 Ohms and
drive the error of power determination even higher (probably on the
order of 50-80%). However, to this point two hours of work is
sufficient to demonstrate this if anyone wishes to confirm my
analysis. To this point a couple of days has revealed no data to have
refuted my analysis. Denial is an option and opinion is free. Even
at this steep discount none step up to the bench. I didn't expect
anyone would anyway. ;-)

73's
Richard Clark, KB7QHC