Topband: 'A cool Beverage Four Pack' QST (April 2006, pp33-36)

[Victor Kean]

> 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