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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 |
#3
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On Jun 13, 10:10*am, Richard Clark wrote:
On Sat, 13 Jun 2009 01:08:24 -0700 (PDT), wrote: Oh well, some more cable along with a UHF/ VHF splitter (combiner) and that big Winegard in the garage will hopefully cure it. By this little snippet of what was intended as an aside may, in fact, be your solution for VHF. *Given your predicament of "code" (arbitrary or otherwise), you can put the cable to work. 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...velopment%20of %20Coll... 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 I hung the spectrum analyzer on the Winegard all channel antenna in the rafters of the garage. The VHF channels are strong and free of response 'bumps' (meaning no serious multipath) and the UHF may be better than the squareshooter on the roof. Tomorrow I shoot a hole in the stucco wall to get the new RG-6 coax (crazy guy at Torrance Electronics sold me 100 ft for $9) pulled in to the splitter to feed the computers and STB. It looks like it will be good. G² |
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