"John - KD5YI" wrote in message
...
On 1/23/2011 11:10 AM, amdx wrote:
I put up a long wire antenna, it is an inverted C.
The antenna is resonant at 3.55 Mhz.
I want to characterize it an the AM broadcast band.
I have made a measurement at 500 Khz and I had to install a parallel
capacitor
to get my variable inductor to bring phase to zero.
I don't know how to do the math to find the impedance of the antenna
with the L and C in the circuit.
Can someone look at my drawing and give me the math so I can figure out
the impedance. Then I can get the numbers at other frequencies for the
band
and calculate those impedances.
See drawing here. I want to calculate the Unknown Impedance.
I need the R and the C of the antenna.
http://i395.photobucket.com/albums/p...naat500Khz.jpg

Thank you, Mikek

Work backwards. You have a 55 ohm resistor in series with a 310 ohm
reactance. Get the equivalent parallel combination of that (the complex
reciprocal). Take the reciprocal of the capacitor (just invert the Xc and
change the sign). Add the two complex numbers. Take the reciprocal of the
answer. This is the impedance the antenna sees looking into the network.
The antenna is the complex conjugate of that (just swap the sign of the
imaginary part).

Does this help?

John

I don't know, I not there yet.

55 + i310
complex reciprocal
55 - i310 / 55^2 + 310^2
reduce
55 - i310 / 3025 + 96100
reduce further
55 - i310 / 99125
Take the reciprocal of the capacitor (just invert the Xc and change the
sign).
Xc = -i717 so 1/i717 ???
Add the two complex numbers.
(55 - i310 / 99125) + (1/i717)
Any mistakes yet?
Going further doesn't get me the answer you have.
Mikek