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The range with the Mast Antenna and this transmitter depends on
ground condition, frequency, the ADF, and atmospheric noise which
in turn depends on location and time. Range for most locations in
the United States with one of the lower priced ADF's is from 50 to
70 miles for frequencies above 250 KHz except over low conductivity
ground. SAC does not recommend this antenna for land installations
at frequencies below 250 KHz. The "T" Antenna is far superior at
all frequencies and should be used whenever space permits. The
50-foot Guyed Mast is recommended for land installations where the
"T" cannot be used. Calculated range over sea water with the Mast
Antenna and this transmitter is 40 miles at 200 KHz, increasing to
i00 miles at 400 KHz.
Ideally, this antenna should be in a clear area; however, this is
very seldom feasible on offshore structures. Large obstacles close
to the antenna will affect the directional properties and the tuning
of the antenna. If possible, the antenna should be installed with
a clear area in the direction of the most traffic.
The Mast Antenna is electrically very similar to a 200 pF capacitor
in series with a small resistor. See the figure at the end of this
section for a plot of the capacitive reactance.
4.2 "H" Antenna
The "H" Antenna is used on the helipad of offshore structures where
there is no clear area to install the Mast Antenna. It is a wire
structure that is installed on the perimeter of the helipad. The
transmitter is mounted directly beneath it so that the vertical
portion of the antenna is the offshore structure itself. Electrical
characteristics vary, depending mostly on the size of the helipad
but are generally similar to the Mast Antenna. Range is also
comparable with the Mast in most cases.
4.3 50-Foot Guyed Mast Antenna
This antenna is a guyed vertical monopole with capacitive top loading
that was designed for land installations where space is limited.
The capacitive top hat consists of six 8-foot radials. The coun-
terpoise system consists of sixteen 60-foot radials made of #i0
copper wire with 6-foot ground rods at each end and one in the
center. The antenna is guyed at the top and center.
The calculated range with the Guyed Mast Antenna exceeds the Mast
Antenna but is less than the "T" Antenna under the same conditions.
This antenna is recommended for land installation where space does
not permit use of the "T" Antenna.
82
Southern Avionics
SS-800AVS
Company
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