John & fellow Topbanders:
"John Harper" <john@ae5x.com>wrote:
Subject: Topband: Fire tower as support for 1/4-wave sloper
> Hello,
>
> I have obtained permission to operate from what I hope will be an ideal
> location (better than my home QTH) for the upcoming ARRL 160 Meter
> Contest -
> a fire tower-like tower, 90 feet tall way up on a hilltop above the
> surrounding terrain with a building at the base with all the creature
> comforts. My plan is to put up a sloper. Although I've never used a sloper
> before on any band, I understand they can be hit or miss as far as
> performance goes.
>
> My question is:
> To achieve resonance, is it better to trim the length of the sloper or
> experiment with the height of where it's fed on the tower?The tower in
> question is steel, about 20' on a side with a steel stairway going up the
> center.
>
> Thanks,
>
> John Harper AE5X
John, I would consider a different approach as well.
An inverted-L 160 feet long, about 80 - 85 feet vertical with the rest
sloping out at less than 30 degrees below horizontal will put out a great
signal over decent radials. I have used such an antenna over 40 - 50
radials each averaging 80 ft length with great success. One does need a 500
pfd variable capacitor to tune out the reactance, as the impedance is about
Zant = 50 + 200j ohms. I have used 500 pfd vacuum variables and 300 pfd
vacuum variable with a 250 pfd vacuum fixed padder with good success.
Another idea: Add 2 to 4 each 40 ft top loading wires to the fire tower and
shunt feed it!
Good luck 73 George K8GG
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