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Old April 6th 04, 08:28 PM
Richard Harrison
 
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Dan Jacobson wrote:
"I will put my wire to work to pull it in even better."

Fitst, you need a line-of-sight path to the desired station. Then, you
need an obstruction in the response to unwanted signals. You need enough
desired signal edge to capture the FM detector and to suppress noise the
undesired signals might add to the mix.

An axial mode helical antenna uses a lot of wire wound into a coil which
is pointed at the desired station, directly or indirectly. Diameter and
coil pitch are optimized for axial gain and directivity.

If a helical coil is small in terms of wavelength, its field is maximum
perpendicular to the coil axis. Such a self-resonant coil makes an
omnidirectional antenna in a plane perpendicular to the coil axis.

We have a rubber ducky as an example of an omnidirectional helix which
is inefficient, limited in bandwidth, but convenient for handie-talkies.
Larger omnidirectional (normal-mode) helices are used by some VHF/UHF
broadcasters to provide circular polarization, but Kraus says on page
173 of his 1950 edition of "Antennas":

"For normal mode the dimensions of the helix must be small compared to
the wavelength, so that from band width and efficiency considerations
this mode is not readily applicable in practice."

There are handie-talkie suppliers and broadcasters who don`t heed Kraus.

Best regards, Richard Harrison, KB5WZI