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Author Topic: 20 Minute 3 band dipole  (Read 6817 times)
ND1W
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Posts: 10




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« on: June 27, 2012, 04:57:38 AM »

While preparing for field day last week I decided to make a multi band dipole so I would have easier band switching and not use a tuner. Off to the laboratory...I found some 3 conductor rotor wire from an old TV rotor, cut the wires to 20, 15, and 10 meters. It took about 20 minutes to make and worked excellent, <1.5 SWR across the bands. So this got me thinking of using ribbon cable to make another one that covers 5, 6, or even 7 bands.
Has anyone tried this?
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W1JKA
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Posts: 1803




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« Reply #1 on: June 27, 2012, 06:00:55 AM »

   Yes,multi band computer ribbon dipoles are a popular antenna for portable qrp operators.As you found out,quick to make ,light and they work.
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WB6BYU
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Posts: 13454




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« Reply #2 on: June 27, 2012, 08:50:22 AM »

But there is more interaction among the different elements when you use multi-conductor wire
rather than separate wires tied off to separate points.  I've used the latter approach for my
portable dipoles over the years - I can put up dipoles for any combination of bands that I
choose each time, and I haven't needed a tuner since I first tuned the wires in a local park
30 years ago.

However, once you get the lengths set, it should work fairly well.  My main concern would
be that, if you built one for 10m through 80m, you'd still need room to put the whole thing
up even if you were only operating 10m and 15m that day.
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VE3WMB
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Posts: 289




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« Reply #3 on: July 04, 2012, 08:19:01 AM »

Another option which you many not have considered is to use a segmented dipole rather than
a parallel dipole. The advantage is that you have no interaction between bands with the segmented dipole and it is easier to tune.
 
Each leg is made up of a single wire that is broken into segments by insulators that can be bridged using jumpers. The idea is the two wire lengths attached to the center insulator form a resonant dipole at the highest band of operation. Jumpers are then used to bridge the end insulators to add-on an extra bit of wire on each end of the dipole that will make the antenna resonate on the next lowest band. This is repeated to cover as many bands as desired. The idea is similar to a trap dipole except instead of traps you are  manually connecting extra wire on the end of each leg to resonate it on a lower band.

This becomes a bit cumbersome when have too many bands but it works well for a few
if you don't mind lowering the antenna to move clip-leads. It is great for portable QRP operation as it can be made out of lightweight wire and requires no tuner for multi-band coverage (each added on section makes the antenna resonant for the next lowest band).

A picture is worth a thousand words so I will refer you to WA3WSJ's excellent write up on this antenna :

http://wa3wsj.homestead.com/iditarod_mini__dipole.pdf

Michael VE3WMB

P.S. I can't say who came up with this idea originally but I remember an article in CQ Magazine
dating back to the late 1970's.

P.P.S. Mine is made out of #24 AWG Teflon coated, silver plated wire and covers 40m/30m/20m which is perfect for use with my Elecraft KX1.
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