If he has an RF bridge, couldn't he simply terminate the tuner's input
with 50 ohms resistive and measure the impedance at the tuner's output?
Well, the conjugate, anyway. I'm trying to imagine the benefit of doing
it that way, rather than simply measuring the impedance at the
transmission line directly.
Chuck,
NT3G
W9DMK (Robert Lay) wrote:
On 31 Jul 2005 21:01:19 -0700, "
wrote:
Hi Group,
I have a pi-network, or at least I believe it is a pi-network in my
antenna tuner. It has two caps to ground and one in series inductor.
If I tune my SWR for 1:1 and go back and measure each value of the
capacitors and inductor, is there a equation or computer program I can
use these measured values to obtain my complex impedance at the input
of the coax cable?
de KJ4UO
I would caution you in regard to measuring the values of the C's and
the L of your pi network. If you actually have an RF bridge or other
test equipment suitable for accurately making such measurements, you
are indeed lucky. Even with such equipment, you should realize that
you will have to disconnect certain components from one another in the
tuner in order to actually make the measurements on each of the three
components. You are also probably going to have to remove some of
those components entirely in order to make the measurements with
reasonably short leads. For anything below 10 MHz, the lead length
will not be a significant factor.
Assuming that you are successful in making the measurements with good
accuracy, the necessary calculations require a good knowledge of
complex numbers and complex arithmetic - much of which is adequately
explained in the Amateur Radio Handbook.
My suggestion at that point would be to simply post your results,
including the frequency of measurement, to this forum and request that
one of us make the calculations for you. I'm sure many, including
myself, would be glad to do that for you. It's the quickest way, by
far.
Bob, W9DMK, Dahlgren, VA
Replace "nobody" with my callsign for e-mail
w9dmkatcrosslinkdotnet
http://www.qsl.net/w9dmk
http://zaffora/f2o.org/W9DMK/W9dmk.html