[Elecraft] folded dipole of topic

[Guy Olinger, K2AV]

----- Original Message ----- 
From: "David Schornak" <dschornak@adelphia.net>

does anyone know of a math to design a folded dipole I know the length
is 468/fMHz but what is the distance between the two wires

-----

The spacing between the wires is not critical.

Most modeling programs have a devil of a time with close spaced
parallel wires. Further, if this is a low-band antenna, height above
ground 1/2 wavelength or less will vary the resonance. The
time-honored tradition serves well. Cut it long, raise it to height,
measure, and prune it onto your desired frequency.

Practically speaking, the worst physical issue with folded dipoles
made from a spool of wire is keeping wires from tangling. This
accounts for the popular use of "window line" or "twin lead" as the
the parallel wires. The velocity factor of these wires is not well
controlled, making the "tune and prune" method necessary. The window
line has a good deal less dielectric loss than the 300 twin lead.

Folded dipoles will tend toward an impedance in the low 200's,
depending on height, which is not related to the characteristic
impedance of the windowline/twinlead. They are also somewhat more
broadband than a dipole. This makes the use of a lightweight 4:1 balun
at the antenna center, 50 ohm feedline and an Elecraft ATU a solution
which covers the entire 75/80 meter band.