"Lew Hodgett" wrote in message
...
wrote:

was told that this dimension was related to the bandwidth one
expected to receive. If so, wouldn't there be a difference in required
length for UHF vs VHS, vs FM, say?

I'll let any Hams on list answer your question; however, 60" covers
everthing including FM in my area.

SFWIW, Radio Shack sells a factory made unit which is 60".

The "accepted" (on FCC tests) simplified equation for a half-wave dipole
wire length is:
feet = 468/MHz.

A folded dipole simply folds each leg of the dipole back to the center.
Effectively, the 5' long folded dipole has 10' of wire. Its resonant
frequency is thus 46.8 MHz according to the formula. Interestingly, this
works out to about a full wave for the 100 MHz FM band. It might be worth
experimenting with slightly shorter lengths, moving the resonant frequency
to, say, 75 MHz. The gains will be minimal, if measurable at all (let alone
noticeable).

The simplified formula differs from the theoretical value in a vacuum by the
velocity factor of the wire, in this case apparently about 95% (from 492/MHz
in a vacuum). I wouldn't worry much about it. The antenna's resonant
frequency is not nearly so important for receive-only operations as it is
for transmitters. A mismatch on a transmitter presents a very high
impedance, causing the feedline to also radiate, and plays all kinds of
havoc to equipment in the vicinity.

A dipole is also somewhat directional, with about 2 dB of gain in its
broadside direction compared to a point radiator. This implies the same 2 dB
attenuation in its side lobes, off the ends. Given a choice, I would face
the antenna toward the signal and the ends toward the local RF noise.
However, if reception is so marginal that this is enough to make or break
the chain, consider it broken and get a tuned, multi-element, directional
antenna. The same goes fiddling with the wire length.