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.

What is the antenna length?


Now as for Al foil as an antenna construction material:

It works electrically, but isn't very strong. Your cardboard tubes
aren't terribly weatherproof either. You might be able to shellac them
heavily. But still it isn't a very good choice.

Making contact with the aluminum could be an issue. Tubular aluminum is
used on antennas, but the connection is usually helped by corrosion
inhibitors, and nuts/bolts with washers to help "dig in" to the AL. Your
thin foil will deform at best, and more likely rip with that sort of
treatment.

- 73 de Mike N3LI -