RadioBanter - View Single Post - Cobra multiband dipole (linear loaded) help pse

December 8th 05, 07:49 PM posted to rec.radio.amateur.antenna

wrote:

Well, not exactly, but close. A half wave on 160 is 260 feet, half of
that is not 140 as in the Cobra and 80 meters half wave is about 134
feet, so half of that is not 70 feet, as in the Cobra antenna. But its
a good enough starting point to work with I suppose. Maybe I'll try 35
feet for 40 meters.

I didn't say anything about wavelength. The 140 ft. Cobra is alleged
to work on 160m. The 70 ft. Cobra is alleged to work on 80m. So a
35 ft. Cobra would be alleged to work on 40m.

Incidentally, I just modeled a 124 ft. Cobra version that has
performance on 160m that is superior to the 140 ft. version
because the SWR on the 450 ohm feedline drops from about 63:1
to about 47:1 according to EZNEC. Performance is comparable to
a 124 ft. dipole on all HF bands. This looks like a fairly
reasonable way to obtain 160m performance from a 124 ft. antenna.
--
73, Cecil, http://www.qsl.net/w5dxp