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[TowerTalk] Multiband dipole made out of rotor wire??

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Subject: [TowerTalk] Multiband dipole made out of rotor wire??
From: (Roger L. Elowitz)
Date: Mon, 19 May 1997 23:22:36 -0400
Hi Steve, NW9G

Pardon my taking some liberty here with your question but.... using flat or
even bundled round rotor control cable for a dipole may cause you more
problems than it's worth.  First off, IMHO,  I don't think the flat wire
will have enough conductor strength to hold up a 160m dipole for very long.
Proximity of conductors becomes a significant factor in adjusting element
lengths so you're in for a big headache there.  Then, if you're still
considering round, multi-conductor cable... how do you propose to get rid of
the conductors that aren't needed beyond the cut.... out toward the ends.
Here you just have extra weight for your under-capacity wire to support
unless you can pull them out of the jacket.

I suggest you scrap the idea and simply go for suspending dipoles below each
other with a common feed point at the center.... as I have done with my
160-80-40 meter dipole.  The 160m dipole is made from #12 stranded wire
(copper clad steel is very difficult to work with and I don't recommend it).
The two other dipoles are #14 stranded.  These numbers aren't critical.  The
trick is what to use to separate them.  Some people use really thin ( 1/2" )
pieces of plastic plastic water pipe or electricians tubing.
The only thing is that I feel they tend to get rather heavy when you have
enough of them.

My recommendation is to find a source of perforated ( 3/16" holes )
fiberglass circuit boards with no foil on either side.  I used 1/2" strips
about 8-inches long between each set of wires.  The fiberglass strips were
spaced about ten feet apart and held in place mechanically by a few turns of
solid copper enameled wire. (Don't bother soldering here.) 

 I also found it necessary to use two, 4-inch fiberglass strips a few inches
out from the center insulator.... which had a coax SO-239 connector molded
into it.

The ends of the 80m antenna were far longer than I actually needed ( a good
idea ) and so I just folded them back on the dipole and twisted them in
place with no end insulators used. I then took a piece of monofilament
fishing line and attached it to the ends of the 80m dipole and secured it to
the 160m support dipole with some tension to pull the 80m dipole sort of
taut. I did the exact same thing for the 40m dipole, suspended below the 80.

I feed the whole shebang with 75-ft of RG-8x for light weight and have the
following data to report for those interested....

One end is about 55-ft up in a tree.... the other end... about 35-ft up in a
tree with the antenna supported by rubber bungee cords as it doglegs past a
TV mast on my house roof.

Absolutely no balun is used or needed since I didn't desire to add weight
and expense to this structure.  Since the dipole runs partially over my
house on one half and the other half runs through branches and leaves... all
over sloping terrain... I doubt you'd find a more unbalanced antenna to
begin with.  IMHO, why would anyone consider such a device for this antenna?
Even Mr.Sevick in his book on Baluns and Ununs says it isn't necessary.

My rough data, measured with an M.C. Jones MicroMatch swr bridge at the end
of the 75-ft feedline.......

Band    Length    Resonant Freq   SWR     2:1 SWR Bndwidth  3:1 SWR BW 
160m    248'-2"      1.890 Mhz            1:1         84 Khz
140 Khz                
  80m    123'-10"    3.795 Mhz         1.5:1       110 Khz
220 Khz                
  40m      68'           7.140 Mhz        105:1       125 Khz
210 Khz

I doubt anyone would find this performance outstanding.  However the antenna
does work nicely and meets all my low band needs without resorting to an
antenna tuner... which I tried to avoid.  At these elevations I'd expect the
dipole to be more or less omnidirectional with some fairly high take-off
angles. I'm not looking for miracles. 

The biggest expense was the wire, the center insulator and the dacron rope
ends all purchased at hamfest flea-markets..  One does not need to purchase
a "kit" for this project unless your aim is to spend extra money.  All you
do need is some hefty end insulators for the 160m dipole that'll take the
weight and tension. Pulleys on the ends help to easily raise and lower the
beast for adjustment purposes which can be many....many....times.

All in all.... it's a real fun project chock full of great learning
experiences. Be sure to clean the copper wire well and solder properly at
the center insulator.... indoors if possible.

Good luck Steve in your multi-band dipole endeavors. Do let us know how you
made out.

Roger, K2JAS


At 01:56 AM 5/19/97 +0000, you wrote:
>Anyone have any luck with swr/performance using rotor wire
>to make a multiband dipole from 160 meters on up?
>What type of rotor wire did you use, flat or the round 
>8 conductor type?
>Thanks in advance and cu on cw.

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