ANTENNA
SELECTION FOR YOUR
PROPERTY
FIRST:
NEXT:
(Based on above – it will be an iterative decision-making-process,
with physical availability, maximizing performance, restrictions &
costs)
Evaluate
your property for three dimensional space with structures like
buildings, trees, fences, etc.
Another
important consideration is covenants (CC&R’s) which puts
restrictions on what type of antennas can be installed. You should
read them first & determine your restrictions. Typically, this
means antennas must be stealth or within the roof of the house or in
the addict. Stealth could mean an American Flag Pole that doubles
as an antenna. Other stealth things could be a wire antenna that is
attached to trees or does not require free standing structures to
hold it up. Some verticals can be telescoped up at night &
lowered during the day. Antennas such as short dipoles, small
loops, or hex beams can be mounted within the roof of your house.
Dipoles-HF,
longest dimension of property is important for 80 meter dipole (over
120 feet or shortest 80 feet with reduced performance). Also height
is important, especially for long distance signals. Less height is
required for higher Freq. bands like 10 mtr (about 15 ft.). Try for
1/2 wave length above grd. or one quarter wave length above grd.
Verticals-HF,
needs area of 360 degrees for radials. Radial wire for 80 mtrs
needs to be 66 plus feet long. Shorter for higher bands like 10
mtrs or about 9 feet (1/4 wavelength).
A
typical multiband 10 thru. 80 meter vertical is 43 feet high.
Minimum four radials per band makes the efficiency of the system at
about 20 percent which will work good. The appropriate number of
radials is about 12-16 per band and less for multi-band verticals
because some of the low HF band radials will work for the higher
band HF frequencies. Note the ends of the radials can be curved
like an (“L”) to accommodate space limitations.
Yagi
antennas are typically for 20 thru 10 mtr and require a structure to
hold them up (tower & a rotator). This drives cost many times
over the cost of a vertical or a dipole. Yagi’s are directional &
will provide long distances with less power & less QRM. The
height for yagi’s is the same for dipoles. Try for one half wave
length high.
A
suggestion would be to Develop your wants & needs & take
measurements of your property & the structures on it, with
pictures. Then get Elmers from the club to walk the property &
make suggestions based on your needs, property configuration &
available funds.
VHF
& UHF antennas are typically small enough that they can be
mounted almost anywhere without generating visible ques. Otherwise
they can be mounted on or in the house.
Costs:
10
thru. 80 mtr dipoles cost about 50 to 300 dollars & about 100
dollars for a thirty foot pole – guyed.
10
thru. 80 mtr 43 foot verticals cost about 300 to 600 dollars with
radials & a balun and/or matching network.
10
thru. 40 mtr 28 foot verticals with a counter-poise are about 300
to 700 plus dollars.
Mono-band
verticals are about 170 to 250 dollars.
Hex
Beam (2 ele.) 6-20 meters about 700 dollars.
3
ele. plus Yagi 10-20 meters full size about 600 to 5 thousand
dollars. Towers cost about 2 – 50 thousand dollars plus
installation.
Home
Brews can reduce costs significantly.
People
have attached their twin lead to aluminum rain gutters, pieces of
pipe, etc and made them work.
Note
– Non-typical antennas require a high capacity matching network
or antenna tuner.
None
of the perspectives above include coax. Good coax is about $1 per
foot.
Safety:
Do
not put an antenna next to the children’s bed room with more than
qrp RF power & operating for long periods.
Get
a perspective of RF exposure to your family and your neighbors
(property line, i.e. public access).
Things
to think about:
Always
use the longest & tallest & highest above the ground
antenna, as you can! This maximizes the efficiency & is
easier to tune.
Many
short (for a band or frequency) antenna’s require manual
manipulation to use more than 25 khz of a band width or to change
bands. Others have remote control to tune the movement in
frequency or bands.
Always
use the best coax you can afford. For example – on 10 meters,
RG-58 has more than twice the loss of signal as LMR400 does per 100
feet (sending & receiving).
First
- Always tune the antenna as close to 50 ohms for the frequency you
will be using. At 25 ohms and above or 100 ohms and below will
work – 2 to 1 SWR.
Always
check the SWR with low pwr (5 watts) and if necessary use an
antenna tuner to provide a good match for the transmitter before
turning the power up.
NUMBER
ONE PRIORITY IS TO PUT SOMETHING UP AND GET ON THE RADIO!!!! EVERY
SO CALLED ANTENNA WORKS!!!
Pictures
of some typical Stealth antennas:
March 2013 Pictures & DocumentsMarch 2013
QUESTIONS? |
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