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Need Ideas for HF Antenna at Fire Station
Our local fire station would like us to provide an HF station to be
operated by hams during an emergencies. They have offered to pay the cost of this. We already have an VHF station there. The problem is the antenna. It cannot be visible (or at least not be at all obvious; they are allowing the VHF antenna on the roof now.). The most likely needed band is 75/80 meters, for in-state communications. So we need high-angle radiation, and a vertical does not seem to be a good choice. The roof is metal, so putting an antenna in the attic will not work. The building is a fairly large 2 or 3 story structure, and in the country with no other buildings nearby. Here are some ideas I have: 1, A horizontal loop, running all around the building up near the top, but somewhat below the metal roof. Would likely be non-resonant, although perhaps we could choose the length. Mount it on stand-off insulators just off the wooden siding. Use white insulated wire and paint all hardware white, to blend in with the white siding. Feed it at some convenient point, perhaps with a 4:1 balun and then coax into the building. Open wire feed would be better, but we cannot get that into the building and down to the station. Use a coax antenna tuner in the station. The SWR would not be good, but the losses of RG/8 at 75M are not that high. Maybe we could use some kind of outdoor automatic tuner directly connected to the antenna, but I don't know of any offhand. 2. Use the rain gutters as an antenna. I did this long ago in a house and it worked fairly well on 40M. Bridge all the joints with copper braid, painted white, to endure reliable connections. At one of the corner downspouts near the ground, connect the center conductor of a coax cable to the downspout. Bury radials extending out from the building an appropriate length, in a 270 degree sector, and connect to the shield. I don't know if the gutters are connected to the metal roof, but if so that might or might not rule out this approach. Use a coax antenna tuner in the station. I know this is basically a top-loaded vertical antenna, but the choices are limited. Comments on both these ideas, and other alternative suggestions, would be greatly appreciated. 73, Bob W8ERD |
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