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