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Building that is made of radio-transparent stuff
has much more possibilities for installing of the helical
antenna. The antenna may be installed almost anywhere in
the house. For example, at the attic, at the ceiling of
the room, may be located on the wall of the building. However
before installation of the helical antenna the place should
be checked on the absences of the electrical wires, metal
pipes and any stuff that may absorb the RF energy.
When the place for installation of the helical antenna
is found it should go to the second stage- to determinate
sizes and design of the helical antenna.
Design
of the Helical Shortened Antenna
As usual at the window opening it is possible install
helical antenna with length in 1- 2 meter. Balcony allows
increase the length to 2- 3.5 meter. Attic and ceiling may
give the increasing in the length of the antenna up to 5
meter. When the length for the helical antenna that may
be installed is found then think about of the band where
the antenna will be operated. Remember that as usual it
is one band antenna.
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At first
try do not use the helical antenna with high Shortened Factor-
more the 10. If it is possible, try use dipole helical antenna.
Of course dipole helical antenna required more space compare
to asymmetrical vertical antenna but it is compensated stable
operation of the antenna. Asymmetrical- vertical helical
antenna required good grounding that sometimes it is not
possible to provide. Some grounding may influence to parameters
of the vertical helical antenna. Device Artificial Ground
very often helps improve the parameters of the grounding
system. References 9 provides design of the device.
When the helical antenna is tuned to
the resonance frequency it should be measured the antenna
input impedance. RF- bridge, MFJ-259 or anyone other device
may do the job.
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