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Aluminum foil capacitance hat
Aluminum foil is fine for the purpose, electrically, but I think you'll
have a dickens of the time maintaining good contact to it. You might even end up creating a rectifying junction which could generate harmonics when transmitting and intermod when receiving. Roy Lewallen, W7EL MGFoster wrote: -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 I've made some Al foil cap. hats for a 34ish foot linearly loaded dipole (based on NN0F's antenna in the ARRL Antenna book, 21st ed, p. 6-35 - he used 6ft wires as cap. hats and 450 ohm ladder wire as the radiator, w/ coax feed). I was wondering if Al foil has enough "umpffh" to act as cap. hat material? Cap hat construction: 45 inch cardboard rolls wrapped in 1-1/2 layers of Al foil (shiny side out). 300 ohm twin-lead (the ant. radiator) leads soldered to copper tape, which was stuck to the Al foil (I check for continuity between the foil & the copper tape & between leads & Al foil they were OK). Final version wrapped in clear packing tape. I attached this ant. to my Elecraft K1 & got 4.7:1 SWR on 80 meters (where I expected it to resonate). On 15 meters got 1.2:1 SWR. Ant. is abt 45 ft above ground, fed by RG58 coax. Ground is concrete. Actually, the ant. is on my apartment bldg roof. That roof is covered in a silver paint or metallic weather-proofing (I don't know). The ground surrounding the apartment bldg is concrete and asphalt. I always select "Very poor - cities, industrial" as a ground description when using the EZNEC pgm. Thanks for any comments. |
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