Dear Mikek: Thank you for your response. Knowing goals is important.

A great deal could be learned by using an antenna modeling computer program
such as EZNEC.

Note that my estimate of the antenna's Z is calculated with one assumption
(some loss in the series inductor) and that its calculations equate 55 + j0
to the impedance of the inductor, capacitor and antenna. Some of the
calculations I have seen seem to assume that one has applied 55 ohms and
then look backwards from the antenna.

Place my estimate of 159 -j526 in parallel with -j717 and then add (the
series) 3 + j310. You should fine the result to be
55.053 -j 0.0711 which is close to 55.

Maximizing the sensitivity of a semiconductor diode detector is probably
done empirically because of the difficulty of finding an appropriate model
for the non-linear detector. Expect that the apparent answer will be
amplitude dependent.

Do report you findings. Regards, Mac

"amdx" wrote in message ...


"J. C. Mc Laughlin" wrote in message
...
Dear Mikek (no call sign):

Assuming that the inductor is 3 +j310 because it must have some loss and
calling the capacitor -j717, my trusty calculator estimates the antenna
looks like 159 -j526. The real part seems high - probably due to ground
losses.

From what I have read it seems very high, could I have 130 ohms of ground
loss?
I don't think so.

I'll be looking into the ground, I think it is just a 6 foot rod, I put it
in years ago.
I'll add FWIW, I connected the AC ground from a receptacle and it made zero
change.

However, the idea that even such a simple an antenna can be modeled as an
R and C over the AM broadcast frequency range seems unlikely.

Ya, that's not the plan, I'll check it every 100 khz and make a graph, with
R and C.


An instrument such as the AIM4170C would provide Z with greater confidence
and do so at each frequency of interest. However, in the broadcast band
it is not clear that such a set of impedances can be used for something
useful. What is the actual goal?

I put the antenna up for multiple use, but to start, I want to use it with a
crystal radio,
the measurements may help me figure out the series cap (range) needed to
make an
R match to the tank circuit over the band.
And it's a project that forces me learn some math.
Thanks, Mikek





Regards, Mac

"amdx" wrote in message ...

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


J. C. Mc Laughlin
Michigan U.S.A.
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