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Author Topic: Multiconductor Cable For Raised Radials  (Read 729 times)
WB4CMB
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Posts: 39




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« on: January 26, 2013, 06:39:44 PM »

1.  If I wished to use multiconductor cable as raised radials, would it work (well) if I cut each of the wires to a seperate resonace for several bands without physically seperating the wires?

2.  If this would not work well what would be the minimum seperation?

I'll try ground radials first, but I would like to experiment with different set ups.

Thanks       Ray
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WB6BYU
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Posts: 13015




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« Reply #1 on: January 26, 2013, 06:48:16 PM »

There will be a lot of interaction among the wire lengths when they are that close
together.  Yes, it can be done.  No, it might not be easy.

Probably the best approach is to cut two such pieces (by overlapping them and
cutting each wire in a different place you may be able to get two such radials using
a total wire length of the longest plus the shortest lengths) and connect them
as a dipole, then tune it up in the normal manner (starting with the longest wire
first.)
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AE5QB
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Posts: 265




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« Reply #2 on: January 26, 2013, 07:50:02 PM »

It is not quite that simple due to the interaction of the different lengths of wire.  If you go to the Bencher website and look at the installation manuals for their verticals, you will see what they recommend for a multiband tuned radial system.  It is made from 300 ohm twinlead.  It is quite expensive and the difficulty with trying to make one's own is finding 300 ohm ladder line of good quality and durability that isn't outrageously priced.

If you just want to experiment then by all means have at it.  Don't be surprised if you can't get it to work well and can't really make heads or tails of what you are seeing.

I am working on a solution to this as well.  I have an HF9V to put on the roof of a school.  There are lots of trade offs and difficulties involved with the mechanical installation of the antenna and radials and keeping it all connected and weatherized/wind resistant and building manager happy.

Good luck in your experimentation.  Have fun with it.
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W5WSS
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Posts: 1644




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« Reply #3 on: January 27, 2013, 12:54:47 AM »

I have a indoor elevated vertical and installed radials.The following are some empirical findings relative to my installation:
They are in tuned pairs of insulated #14 copper wire quarter wave length that are installed horizontally and symmetrically routed traveling away and opposite in direction from each other around the room baseboard evenly and had to be almost bundled together but are slightly fanned relative to each set.

5 sets of two. 10m 12m 15m 17m 20m.

I knew that Their specific interaction would be difficult to predict.

I actually achieved a tuned each set and managed to get a 50 ohm non inductive matched system along with a narrowing of passband and proper current and voltage measurements....but could Not get the 15m band isolated from some destructive mutual coupling until I disconnected  all the pairs from the feed point except the 10m set while attaching them to a common junction just below the vertical base.
Then
 Everything resonated slightly shorter than formula relative to loading effects but radiation is excellent and the matched system allows me to use a feedline length in a matched state that enables me to have all the equipment located on the far opposite side of the house.

The feedline could not be routed along the same radials path however, I needed to maintain a 45 degree angle route relative to their travel. 

Elevated Radials do radiate about -40 to -50db of remnant horizontal radiation even when everything is optimal and will couple when they are close relative to each other.

This system is a variant due to being elevated and indoors and radials are isolated from the Earth surface etc.

Results are unpredictable pattern development and coupling re radiation of nearby conductors but does offer some hf work for an otherwise impossible situation.  73



 
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WI4P
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Posts: 42




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« Reply #4 on: January 29, 2013, 12:52:07 PM »

Made a 10/15 meter vertical as a novice in 1976 using plans in an ARRL newsletter called New Ham News.  It used two lengths 300 ohn tv twinlead for the radiating elements and 4 conductor rotor cable ( split in two ) for the ground plane radials.  Can't get more close spaced than this.  It worked quite well as measured and cut with no pruning that I can recall.  The pi-network in my Tempo One tube type rig loaded it very well.  Rotor cable is failry inexpensive.  Why not give it a try.
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