In article ,
Jerry wrote:

Thanks Jerry. No you aren't missing anything other than the fact that
my familiarity with Smith Chart analysis is limited to working through
a few exercises in the last chapter of the ARRL Antenna book. I will
be looking for more Smith Chart tutorial info on the web and am
certain I can get myself up to speed enough to start working with
conductance, suseptance, admittance, etc.

I strongly encourage you to work it through from the basic math:

- Impedances and admittances are complex numbers, with both real
(pure-resistive) and imaginary (reactive) components.

- When you put two things in series, add their impedances

- When you put two things in parallel, add their admittances

- Admittance = (1+j0) / impedance, and vice versa.

The math is quite easy to implement in FORTRAN, or any other
programming language which has native complex-number capability. C
doesn't, alas, and you'd have to use a complex-number library or write
your own. I'm sure that there are standard C++ classes and methods
for handling complex numbers.

Although I haven't yet used the capability, it looks to me as if
modern spreadsheet systems (e.g. Excel, OpenOffice Calc) can deal with
complex numbers. You can't use the normal arithmetic operators (at
least, not in OpenOffice Calc) but myst use special complex-number
functions such as IMPRODUCT and IMDIV and IMSUM.

Not too hard to do, though.

I'd suggest starting out with the simplest calculation (e.g. a
inductor or capacitor, in series with a pure resistance). That one's
really easy, you just calculate the impedance of the reactive
component at the frequency of interest, and do a complex addition.

Then, do an inductor or capacitor, shunted in parallel with a pure
resistance... calculate the reactive impedance, invert the impedances
to get admittances, sum them, invert again to get the final impedance.

Once you can do those two basic steps, you can simply repeat them as
necessary to determine the effect of L and T matching networks, tanks,
and so forth.

The Smith chart makes it easy to do this via graphical means - it's
faster than using a slide rule or table of logarithms - but it's very
instructive to do the math youself (with the aid of a spreadsheet).

With the Smith chart, it's usual to normalize all of the impedances to
your reference value (e.g. divide by 50 ohms), do the calculations,
and then denormalize (e.g. multiply by 50 ohms).

Doing so isn't necessary if you do the complex-number calculations
yourself... you *can* normalize/denormalize if you wish, but you'll
get the same results if you work directly with the raw impedances and
admittances.

--
Dave Platt AE6EO
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