Grant wrote:
>>> Or the inverse as I did, cut my T for the low end of the band. Then three
>>> series capacitors with PCB relays to short each individually (none, 1, 2,
>>> or 3) yielded nearly full band coverage <1.5:1 swr. My T is 85' to top and
>>> a 50:25 ohm TLT is a close match, then the capacitor stack follows.
I modeled Grant's configuration with AutoEZ, mostly to see how the optimizer
would handle things. I ended up with capacitor values quite different from
Grant's 4000/2000/1333 pF, but part of that could be because my modeled
conditions do not equal Grant's reality. Here's a full-band SWR sweep which
also shows the values I used for the variables.
https://postimg.cc/image/6o9yxez4h/
Bob wrote:
>>> A simple T antenna will have a radiation resistance of 10-12 Ohms with
>>> electrical height of say 43ft with a Good ground system of quarter wave
>>> radials.
So then I went back and modeled something similar to what Bob described. For
this one I first optimized on both the height of the vertical portion and the
length of the T arms to get a feedpoint Z very close to 12.5+j0 at 1975 kHz
with no series coil. Then I optimized the inductance values for the three
lower band segments all at once.
https://postimg.cc/image/3u6tk1241/
AutoEZ users, if you'd like to see the optimizer setup and the trick for making
the capacitance/inductance values frequency-agile just drop me a note via
private email and I'll send you the models (*.weq files).
Dan, AC6LA
https://ac6la.com/
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