ANTENTOP-
01- 2005, # 007
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Building Antennas
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by Igor Grigorov, VA3ZNW
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Almost all modern buildings contain lots metal parts inside.
For example, any building has water pipes (as a rule copper), main
wires, telephone wires, inner metal skeleton. Some building has
a water (steam) heating system. The hidden metal parts can work
as transmitting antenna. You only have to connect your transmitter
to the metal in proper way.
In this article we discus antennas based on domestic water heater system.
Let's name the antennas "Water Heater Antenna System",
or just WHAS. Certainly, diagram directivity and efficiency of WHAS
often are far from desirable. Anyway such antennas allow ham to
be on the Air.
Base of WHAS
Water steam pipes, which go from down to up through a building,
create hidden metal structure. The question is: in what manner we
can connect to the pipes in order to these ones work like an antenna.
Below we discuss several ways how to do it.
Before you go to create your own WHAS please keep in mind the advice.
Do not use powerful TX, limit your power to 50 (and below) watts.
At large power, at first you may do a burn to your neighbors, at
second large power can create unhealthy electromagnetic environment
at your place.
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A Good Antenna
for the 160 meters
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My experiments
show that there is no big difference in operation between WHAS designed
either in brick or inside concrete building.
At my experiments WHAS lose 2- 6 balls (at scale RS) to outdoor
antennas. As rule WHAS lose more at operation on the higher HF amateurs
bands. Efficiency WHAS dramatically falls from the 12-m band. However
the antennas can work very well at the 160- 30 meters. By one from
the bands WHAS sometimes work better the outdoor antennas. As rule
WHAS is very noisy at working on receiving, so, use a separately
receiving antenna.
WHAS with Gamma Matching
WHAS used gamma matching is very simple in design and good
in work. Fig. 1 shows the
design. As rule the WHAS works not bad on the most of ham HF bands. |
Electrical contact to battery of heating is done at two
places, one near the ceiling another close to the battery of heating.
Wire of gamma matching is located approximately in 5- 10 centimeters
from the pipe of heating. For fixing the distance it is possible
to use empty plastic bottles from soft drinks. The WHAS is connected
to TX through an ATU. Ground of the ATU is connected to battery
of heating. For better work the WHAS install ferrite rings (5- 20
ring with any permeability) at two ends of the coaxial cable going
from TX to ATU.
Two Wire Line WHAS
The WHAS works not at all location. Make an experiment at your place to
check its work. Sometimes at some location the WHAS works very
well. The WHAS has only one advantage - this one is very simple
in design. Fig. 2 shows the design. The pipes are connected
to an ATU by any two wire open line or just by single wires.
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