Terry,
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
Lmatch 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.
73,
Dave G3UEG
>Dave,
>
>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
>matching network.
>
>Hope this helps. I'll forward Dave a copy of my EZNEC file.
>
>73, Terry N6RY
>
>
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