On Tue, 5 Feb 2002 "Sain'T Tom" <k4rv@mindspring.com> writes:
>
> Anybody got any REAL WORLD and WORKING height dimensions
> of a 160 meter quarter wave vertical made of Rohn 25?
>
> Thanks
> Tom K4RV
>
The ARRL Antenna Books (and Handbooks?) have a graph showing
% of freespace length vs. L/D ratio of the 1/2 WL wire (or element).
I believe someone indicated that Rohn 25 could be modeled
as a cylinder of 8 or 9 inches diameter,
OR, you could model it as 3 cylinders of 1-1/4 inch diameter
in a triangle 11-1/4 inches center to center with the ends
connected. I assume you are not planning for any other
antennas on the tower / vertical.
If you are going to shunt feed it, anything close will work.
Tom N4KG
OK, here are the numbers...
Speed of light = 300,000,000 meters / sec = 984,000,000 ft/sec
Frequency = 1,800,000 cycles / sec
1/2 WL = ( 984,000,000 / 2 ) / 1,800,000 = 273.3 ft
Length / Diameter ratio for 1/2 WL = 273.3 / ~0.7 = 390
"K Factor" for L/D ratio of 400 ~= 0.97
1/2 WL at 8.5 inches OD = 273.3 X 0.97 = 265 ft
1/4 WL = 132.5 ft
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