home
***
CD-ROM
|
disk
|
FTP
|
other
***
search
/
Ham Radio 2000
/
Ham Radio 2000.iso
/
ham2000
/
antenna
/
antennas
/
vhfuhf1.art
< prev
next >
Wrap
Text File
|
1994-05-30
|
5KB
|
113 lines
SUBJECT: VHF & UHF Hidden antennas for PUDs/Condos/Apartments
These antennas are much easier to hide because of their size.
I'll get into some high level design concepts here and expound on
them later.
I'll be discussing the following antennas:
o Stealth Verticals
o Stealth Beams
o Indoor Antennas
o Indoor/Outdoor use of Mobile Antennas
o Field Day / Portable
---------------------------------------------------------------
Stealth Verticals:
This type of VHF / UHF antenna is very popular with amateurs. The are
easy to build and install. Many commercial antennas are available, but
for the dollar, an amateur can build a superior VHF or UHF antenna for
the base or mobile use. For the PUD/Condo/Apartment user, even a simple
vertical can be a major problem to install. Location in an apartment may
be one of the biggest problems facing an amateur when antennas are
prohibited.
There are large multi-element verticals on the market such as Comet and
Diamond. The size of these antennas makes these a bit more difficult to
install. There are other homebrew antennas that can be installed however.
These antennas will be discussed here.
J-Pole
The J-Pole is an exceptionally good antenna and easy to build if the
directions in the ARRL handbook are followed correctly. One modification
I recomend for the J-Pole is to solder the tuning connections after the
SWR is set. This allows for 'no maintenance' on the J-pole and no
surprizes with SWR changes due to corrosion.
1/4, 3/4 wave ground planes
These ground planes offer unity and 3dB respecfully. These antennas
do not need coils or tuning circuits to accomplish their action.
Discones
This antenna can be homebrewed or bought commercially. The discone is an
excellent antenna, but has it's drawbacks in hiding. The antenna has unity
gain and can be used on multiple bands.
Vertical Dipole
This antenna can be put together in various configurations with various
matching devices. The dipole is a halfwave.
Full Wave Loop
This antenna can be configured to vertical polarization. It is not omni, but
exhibits good gain in a bidirectional pattern.
There are many more antennas that exist. Some are larger, some don't have
the bandwidth, and still others require coils & capacitors to make them
work. The aboved mentioned antennas are easy to homebrew and make for
good antennas that can be used by PUD / Condo / Apartment dwellers. All
the above antennas are in the ARRL antenna book. The design and
construction of these antennas is easy if the directions are followed in the
book. What I intend to accomplish here is placing the antennas such that
they go unseen by all.
-----------------------------------------------------------------------
INSTALLATION OUTSIDE
Let's look at the first one: The J-Pole. Gain wise, this antenna exhibits
about 1.8 bDi of gain on transmit and recieve. If you make your J-Pole from
brass rod or like material, placement of the antenna should be accomplished
fairly easy. You should remember not to install the antenna near other metal
objects or fixtures. Give it about three feet of room from conducting
surfaces.
The best hidden J-Pole I've seen was painted to match the chimney brick work.
Everything that went with the antenna was matched to the chimney. The coax
was painted to match not only the chimney, but the roof and then the paint
color on the side of this PUD home. The J-Pole was bent to the contours of
the brickwork and masonery. The amateur installed the antenna under the cover
of cleaning and repairing the chimney. His plan worked well.
Another J-Pole I've (almost) seen was mounted to side of a tree at thirty
feet. It too was painted to match the bark of the tree.
I designed and built a J-Pole for a friend that looked and matched the
foliage of a white pine. I used artificial plastic Christmas tree elements
to match a branch on the pine tree. If you didn't see where it was installed,
you couldn't tell it from the rest of the tree.
Another design was mounted to a swing out arm which was installed under
a window sill at thirty feet. The Ham painted the J-Pole to match the
natural wood finish on the condo. At night, he would swing the J-Pole
out from the window and talk on the local repeaters. The dark color of
the J-Pole, helped the amateur, by blending the antenna against the
night sky.
*** END PART ONE ***
-WS