"Jim Lux" wrote in message
...
Jerry wrote:
"dykesc" wrote in message
...
On Jun 4, 2:10 am, Ian Wade G3NRW wrote:

Is this any help?

http://www.wy2u.com/

Scroll down to "Electrical / Electronic Engineering Links" and click on
"L/C Impedance Matching Design Tool"

--
73
Ian, G3NRW

Thanks Ian. That is the type of calculator I am looking for. However,
this one requires both source and load impedance as input. I am
looking for one that will allow you to specify the source impedance
(50+j0), fill in the capacitor and inductor values, and then tell you
what the matched load side impedance is.

Hi dykesc

I may be missing something. But, if the objective it to learn if the
local 105 MHz signal is actually introducing error into your impedance
measurement, only a few Smith Chart Polts are needed. You know the path
(on the Chart) the shunt reactance will have taken while being adjusted
to make a "match". You also know the path the series reactance took.
Start from the Chart center and move the impedance along the circles of
constant resistance for the series reactor. Move along the circles of
constant admittance for the shunt reactance. When the Xc and Xl are
both known, and you know which is closest to the "transmitter", it seems
that a "program" is unnecessary. What am I mising?


Fine, for doing a couple or three. Now do it for a dozen measurements at
different frequencies, especially if you have to convert L and C into Z
for each measurement. A program or spreadsheet is nice to have, because it
automates the tedious calculation.

Heck, if you have a RS-232 interface to the antenna tuner, you can
automate the whole process. Quod fecit.

By the way, the assumption that the run of the mill ham rig has a 50 ohm
resistive output impedance is not necessarily valid. In practice, nobody
cares.. they just adjust until the reflected power is minimized. But if
you're trying to use the tuner as a measuring instrument (essentially, the
variable part of an impedance bridge), it's important.

Hi Jim

As you can see, this plan to 'double check" antenna impedance by relating
the impedance to that which the tuner produces, is very limited in its
accuracy. One might say *why bother*. My thought was/is, the original
poster asked for an online calculator. When that calculator was given, and
he still asked for more, I thought it would be helpful to point out how easy
it is to use the Smith Chart to get some insight into evaluating his
impedance meter. It is my opinion that extensive calculations with a
computer program are not able to provide any exact answer to the question
about actual antenna impedance when only the tuner Xl and Xc are known. The
Smith Chart is a great tool for estimating how impedance matching can be
realized. I assummed that the OP could possibly benefit from knowing how
easy it is to estimate antenna impedance using the Smith Chart if it can be
assummed that the LC circuit is known and that the resultant impedance is 50
ohms. Shunt reactances move the impedance along the circles of constant
1/R and series reactances along the circles of constant R.

Jerry KD6JDJ