Dear Walt,

Ever since reading your 1973 QST articles, being a second-year student at
the Polytechnics/Technical University of Copenhagen, I have referred to
your ground-breaking work for removing the myths and misunderstandings of
the (un)importance of the swr over and over again. Somewhere I still have
the ageing photocopies of all the articles. But having the opportunity to
get it all and more in one piece in Reflections III is really greast. I
have ordered my copy right away.

Later on, both in my professional life after receiving my MSc(EE) as a
radio engineer and during my 19 years as Technical Editor of 'OZ' (the
Danisk QST) I have had to weed out misconceptions about swr and
transmission lines. My early understanding from your work was a great
help. Thanks!

All the best,

vy 73
OZ7S Sven

Got delivery to-day.

As mentioned earlier, most of the stuff is old hat to me - but I really look
forward to dig into the chapters concerning tx output impedance. A highly
controversial subject for decades.

vy 73
OZ7S Sven

Hello Sven,

Glad you received your copy today. To pique your interest in tx output
impedance, Chapter 19 will do that for you, especially Sec 19.14 on
Page 19.22. This section describes in detail, in fourteen steps, how
the output Z is measured.

I've seen a lot of discussion on this subject, and most of it shows
that many who discuss it don't have a clue to the correct answer.
Which is why I have made many measurements of the output Z to
determine the truth.

The output Z is determined principally by the proper adjustment of the
tank circuit with respect to the load. I'm talking now only about tube
amps with pi-network tank circuit coupling the amp tube to the load. I
cannot comment on solid-state rigs, or those that have no tuning
adjustments.

There are those who believe that the output Z = 50 + j0, and there are
those who believe the Z is much higher. Here's what really happens.
With any practical grid drive, load and tune the amp into a 50 + j0
dummy load to deliver all the available power. In this case the output
Z of the amp will be 50 + j0 ohms.

Now add 50 ohms of inductive reactance to the same dummy load. The
result is now a load impedance of 50 + j50 ohms. Now reload and retune
the pi-network to again deliver all the available power into the new
complex-impedance load. The new output Z? 50 - j50 ohms, the conjugate
of the complex load impedance. In other words, to determine the output
Z of the amp, simply load it into an impedance of known value such
that all the available power is delivered at a reasonable drive level.
The output Z is then the conjugate of the load impedance.

You say you want proof of this simplistic procedure? Fine. It's all
right there in the fourteen steps in Sec 19.14 that describe the
entire measurement procedure. I'm sure you'll find the procedure
enlightening.

Walt, W2DU