On Wed, 02 Apr 1997 12:49:37 EST, wa5whn@juno.com (Jay D Miller)
wrote:
>QRP-Lers,
>
>
> If You have access to 300 ohm ribbon twin lead, cut one-half of the
>dipole for 30 meters (one side of the ribbon cable, one ribbon cable can
>make 2 dipoles), then the bottom half part of the twin lead for 20
>meters, that way, You have a 300 ohm ribbon twin lead, with the top part
>of the ribbon cable, cut for 30 meters (1/2 wave) & the bottom half for
>20 meters (1/2 wave). I had made up another one, for 17 & 15 meters. They
>are feed, at the center, with RG-174, no traps, no tuners, and they roll
>up nicely into my back pack with either my Sierra (N6KR design) or
>GM-30/20/17/15 combo (NN1G design). The idea for this is from "The ARRL
>Antenna Book", 14th edition, 1982, page 8-3. I was looking for light
>weight antennas, for hiking around in the Mountains. For example, You
>could build (I have not done this combo yet) a 40/30 meter dipole with
>300 ohm ribbon twin lead, where the upper part of the ribbon cable (top
>wire) is cut for 40 meters & the bottom half (bottom wire) is cut for 30
>meters. You will find using the old 468/Freq. (MHz) will make this dual
>combination a bit long, but You can prune it. If none of this makes any
>sense, I can upload a few *.JPG files on to the W5BI web page, and show
>You what I am talking about. Essentially, You take 300 ohm ribbon twin
>lead, trim the top wire part of the cable for 40 meters, the bottom part
>of the cable for 30 meters. It becomes a dual band (resonant) antenna,
>light weight. All fed with one feed line, tied to 3 insulators.
>
> What You have is a dual band antenna, using 3 insulators, fed with one
>piece of coax, in the center. In this case, RG-174 for QRP purposes.
>RG-58 for QRP & QRO purposes.
I did this with 450 ohm ladder line -- for 40/30, it took 56.5 ft.
total, cut as follows:
|cut here
_______________________ ___________________
40m - 33 ft. 30m - 23.5 ft.
_______________ ___________________________
30m - 23.5 ft. |cut here 40m - 33 ft.
Cut the space between the wires (9.5 ft), and trim to resonance.
This uses the 468/f formula, and works out a bit long, so you have
room to trim. Might want to add 6" or so, if you are unsure.
72 es 73 de
Marty, KM7W
__________________________________________________________________
Jackson, Tennessee e-mail: mdwatt@usit.net
http://www.public.usit.net/mdwatt
"The Curmudgeon's Corner"
NorCal #???? - ARCI #7514 - QRP-L #953 - AK/QRP #098 - Grid EM55oq
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