On Sat, 13 Jun 2009 10:10:24 -0700, Richard Clark
wrote:
(...)
The solution is called a "Franklin Antenna." It would be disguised as
an antenna cable (or telephone cable, or power line, or other
innocuous wire) that trails up (to something innocuous), but never
connects (who is going to look? and if they did, it could always be a
dummy connection).
A Franklin antenna is a stacked, gain antenna that is very colinear
(hence the cable motif). These are most often described on the Web
for home wi-fi or bluetooth applications, but with scaling you can
bring them back down into the TV VHF band. A quick search gives:
http://www.para.org.ph/membersarticl...s%20-%2021.pdf
which on page 11 gives a pictorial representation (I can't say I vouch
for the entire paper, but it is representative of the topic).
73's
Richard Clark, KB7QHC
The only problem is that a Franklin antenna is usually vertically
polarized. TV is horizontal.... well some station have a vertically
polarized component, but it's mostly horizontal.
http://www.tvtechnology.com/article/68820
The Franklin antenna is not very wide band, covering perhaps a few UHF
channels, but certainly not the entire UHF TV band.
Topic drift: Franklin or AMOS antennas for Wi-Fi. NEC2 deck is under
the "main" page and is easily scaled for your favorite TV channel.
http://802.11junk.com/jeffl/antennas/AMOS-7/index.html
http://802.11junk.com/jeffl/antennas/AMOS-5/index.html
I don't have photos of the "disguise" TV antenna I installed on top of
a 175ft redwood tree. It was vertically polarized, crammed into a PVC
pipe, and filled with urethane foam (fence post compound). 20dB gain
wide band GaAsFET amp at the base. It was painted brown, to match the
tree trunk.
Performance was a disaster. There wasn't enough gain so most stations
were noisy. With an omnidirectinal pattern, it did a superior job of
converting reflections from the surrounding mountains, into obnoxious
and irritating ghosts. 4 tries, and no luck.
The plan was to install a pully near the top of the tree, and use a
rope to raise and lower verious experiments. Unfortunately, I used a
rope that did not do well in the sun. After about a year of trial and
error, the rope crumbled. The pully is still in the tree and can
probably be used again.
As for other disguise antennas, I've done some tinkering
characterizing various road signs for operation as antennas. The
aluminum sign is a tolerable radiator, but the galvanized steel
support is a problem. I've also seen all manner of urethane
sculptures, designed to resemble a tree, cactus, building materials,
lamps, boulders, etc, each with an antenna behind or inside. Also
fiberglass panels for hiding antennas in the sidewalk.
I've also crammed wi-fi repeaters inside a plastic owl. I've
disguised a wi-fi antenna by making it look like a giant bird nest. If
the neighbors asked, I told the owner to tell them it was a Roc nest.
http://en.wikipedia.org/wiki/Roc_(mythology)
For HF, I've loaded into the rain gutters, installed chicken wire
under the carpeting for a ground, and strung wires between telephone
poles.
--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060
http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558