> I have the basic idea of how it works , but does the
> parallel wire need to be 450 or 300 Ohm ribbon or will
> any 2 parallel wires do ? Is the impedance important ?
Robert:
Any 2 parallel wires will do, although matching probably
helps to maximize the apparent directivity. If the unused
port of the 2 wire Beverage is not matched, then the "other"
port is looking into an unterminated (or poorly terminated)
Beverage, and the uni-directional characteristic suffers.
I use a pair of #14 wires spaced 9 inches 8 feet above ground
which has an impedance very close to 675 ohms. Then, 9:1
transformers (3:1 turns ratio) make a decent match to75 ohm
cable-TV feedline (RG-6).
Some other interesting combinations:
450 ohms: #12 spaced 1.75 inches, 8 feet above ground
450 ohms: #14 spaced 1.375 inches, 8 feet above ground
I've used the following formula in a spreadsheet to calculate
a few open wire impedances:
Z=276*LOG(2*B3/B2)*SQRT((1+B3/(2*B4)*B3/(2*B4)))
where Z is the balannced impedance, B2 is wire diameter, B3
is distance between wires, and B4 is height above ground, all
in the same units.
I forget where I found this formula, but a little Googling could
probably find it. The results seems to match data in other
places, such as in Misek's book.
Victor, K1LT
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