Hi Guys,
I'm looking for someone to model a simple Shunt-Fed tower for use on
80-meters. I have no experience using modeling software and don't have time
to
learn until after I retire, so I'm hoping someone is willing to model this
for me.
I'd like to model this tower to help determine the aprx. location of the
50 ohm resistive feed point tap at a frequency of 3.550 mhz. I realize
that I could feed the tower at almost any height and make it work using a LC
Network, but I'd like to keep it simple as W8JI once wrote, by using: "a
simple gamma capacitor and shunt feed conductor with the tap point adjusted to
find 50 ohms resistive". (no inductor required with this simple feed
method) Since the tower is short at 46', it will be relatively easy to climb
it in order to find the exact 50 ohm resistive tap location. However, with
my bad back, modeling it should get me in the general area of the 50 ohm
tap location and save me several trips up and down the tower which would be
much appreciated.
Here's the tower specs:
1) Rohn 45 tower with 18" face width, tower height is 46'.
2) Non-Conductive guy wires. (no steel guy wires)
3) Top mounted Bencher Skyhawk Tribander. (24' boom)
4) 10' aluminum DC grounded VHF antenna top mounted, extends the overall
tower/antenna height to 56'.
5) Proposed Shunt Feed system: 10 gauge copper wire run parallel to the
tower, from the base of the tower upward to the 50 ohm resistive tap point.
I'm flexible with the spacing distance of the wire from the tower, but am
leaning towards an 18" separation unless modeling recommends otherwise.
In addition to determining the estimated 50 ohm resistive tap height, it
would also be very helpful if the modeling software would estimate the value
of the needed capacitance. (such as 150pf)
Thanks & 73!
Dick- K9OM
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