EMRFD Message Archive 4898

Message Date From Subject
4898 2010-08-14 18:20:50 aa7hq two-element antenna tuners
now i am about to turn 90. mother nature has given me lots
of time to think about some favorite topics. the book emrfd,
and some acquaintance with the authors, has led me to some
ideas i want to share with any readers of a like mind.

however, i note that many posts on emfrd fail my PCB index:
piffle, claptrap, and balderdash. the commonest sin is using a
word to mean what ever the user wants rather than the generally
accepted meaning. (i was once the village idiot for asking some
who had impulse responses for a receiver to share them. of
course, there were none.)

i have been thinking about antenna tuners of the two element
kind, maybe a series inductance and a shunt capacitance i
visualize it in a circular impedance chart, a Smith chart. this
chart is normalized to 1. this is to take advantage of symmetry
between impedance and admittance, and to eliminate all those
two-pi mistakes. further, the shunt element and the series element
take the forms z=2j, or z=j, or z=j/2, and y=-j/2, -j, -2j etc.

there are 64 possible loads for any one such tuner for which
SWR =1. if you calculate these, and plot them on a Smith chart,
all will be clear!

you can easily see the result of adding switched elements you can
guess at the impedance at the midpoint of the curvilinear squares
and estimate the SWRs at the "bumps".

you can easily see what happens if you use a frequency 2f, f/2, etc.

i got started on this by the suggestion to tune a three element tuner
by a rule of thumb"! as Dorothy Parker used to say, it made me want to fwow up!

if you like this, tell me. if you don't, just go away! we nonagenarians-about-to
be don't give a hang for any scolding by the hot dogs!

warmest regards,
ed, aa7hq
4899 2010-08-14 19:05:52 Phil Sittner Re: two-element antenna tuners

If there is a first part of your thread I have missed it and if you have initiated it please go on! This is my most favorite forum and people share the most wonderful and intuitive ideas so encouragement is tantamount. Understanding is founded on the most basic of ideas and your topic is absolutely mainstream.

Do it.

Phil kd6rm
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4903 2010-08-15 21:25:38 KK7B Re: two-element antenna tuners
Hi Ed,

This is really cool. I've read your post 3 times now, and each time it gets cleverer and cleverer. Mother nature appears to have been kind indeed--your are as sharp as ever.

I can't help wonder if this was Phil Smith's initial exercise. The more famous of his many charts falls out quite naturally.

Best Regards,


4907 2010-08-16 09:51:45 aa7hq@comcast.net Re: two-element antenna tuners
it's probable that hundreds of people have viewed tuners from the normalized
point of view, and very nice to conjecture that Smith did it! my objective
is to get a few more to realize that using the Smith chart is not very difficult,
and is VERY useful.

and thank you for the kind words!

regards, ed

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