Thanks very much for the model and the explanation and taking the
time to do it...
I see what you have done, in that the capacitor has gone to ground
effectively in parallel with the coil.
My thinking is that the series C does indeed go to earth but
**through** the 50ohm resistive source impedance.
Is it just a convention that this resistance can be ignored in the
model? The proof is that it seems to work without it..
I have got TLW on a CD somewhere, I must look it out and load it onto
this (new) PC.
I should just say that I made a small mistake in the previous post in
that the vertical was only 37ft high (not 48) so that was why my
L-match components were different from yours. (I have been playing
with several different models and got them mixed up) I have modified
your model to the correct values.
Thanks again for your help.
>My EZNEC model may be a little different than yours. I used 3
>sections of 16 feet each with 2.5, 2.25 and 2 inch diameters (64
>segments each), then inserted a 0.25 foot section of 2.5 inch (1
>segment) at the base where I place the source. With no matching I
>got 425.5 -j 536.7 ohms (MININEC ground).
>I put that into TLW, from the ARRL antenna book. It produced a shunt
>L of 2.93 uH (Q=200) and a series C of 68.7 pf (Q=1000). TLW says
>the loss in this network is 0.15 dB.
>I added a 0.25 foot piece of 2.5 inch conductor horizontal and a 0.25
>foot piece to ground, where I placed the inductor. The series C went
>on the base segment along with the source. The impedance was now
>47.4 -j 4.5 ohms. The resonance occurs at 10.175 MHz, where the
>impedance is 48.9 ohms.
>One issue is that this antenna is very close to 1/2 wavelength long,
>and the impedance is very sensitive to segmentation, even without the
>Hope this helps. I'll forward Dave a copy of my EZNEC file.
>73, Terry N6RY
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