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[TowerTalk] Forked Radial System

To: <towertalk@contesting.com>
Subject: [TowerTalk] Forked Radial System
From: eric@k3na.org (Eric Scace)
Date: Mon, 15 Jan 2001 11:15:55 +0300
   I was actually wondering about this arrangement the other night.  Has anyone 
tried it in the field or with NEC4?

-- Eric R3/K3NA

-----Original Message-----
From: owner-towertalk@contesting.com
[mailto:owner-towertalk@contesting.com]On Behalf Of Mark .
Sent: 2001 January 12 Fri 19:14
To: towertalk@contesting.com
Subject: [TowerTalk] Forked Radial System


Greetings Gang;

I have been following the discussion of counterpoise systems for 0.25 
vertical radiators with great interest.
I especially liked the suggestion to use forked radials. It occurred to me, 
after reading all the posts so far, that there is a potential for a 
substantial savings in wire while maintaining counterpoise effectiveness, if 
we allow a maximum gap of 0.05 wavelengths between conductors in the 
counterpoise.

One easy way to implement a forked radial scheme is to split each radial at 
the 0.125 wavelength length, into two more forks of 0.125 wavelength. This 
way, all the pieces can be precut to the same dimension during fabrication. 
Each radial has 3 pieces of wire, all the same length, with an overall 
length of 0.25 wavelengths.

The resulting ground screen looks like a snowflake having a radius of 0.25 
wavelengths.
I guess this might be described as a semi-fractal design.

Here's a case comparison of three schemes for what should be nearly 
equivalent counterpoise systems and the raw wire required to implement them. 
Note the wire savings for the "FORK 15" counterpoise system. If a shortened 
vertical radiator is used (less than 0.25 wavelength), I think shortened 
radials can be used with only a very small reduction in efficiency, if I 
understand the literature correctly. Accepting this, then the potential 
exists for even more wire savings if you select a reduced radial length as 
well.

Case 1: " CONVENTIONAL 60" radial system
  60 x 0.25 wavelength radials
  Number of wires: 60
  Maximum conductor spacing: 0.026 wavelength, at the outside ends
  Expected efficiency: Almost perfect
  Total wire length required: 15 wavelengths

Case 2: "FORK 30" radial system
  30 x 0.125 wavelength radials
  60 x 0.125 wavelength radials
  Number of wires: 90 x 0.125 wavelength
  Maximum conductor spacing: 0.026 wavelength, at the fork junctions and 
outside ends
  Expected efficiency: Almost perfect
  Total wire length required: 11.25 wavelengths

Case 3: "FORK 15" radial system
  15 x 0.125 wavelength radials
  30 x 0.125 wavelength radials
  Number of wires: 45 x 0.125 wavelength
  Maximum conductor spacing: 0.05 wavelength, at the fork junctions and 
outside ends
  Expected efficiency: Within 0.25 dB of conventional 60 radial system
  Total wire length required: 5.625 wavelengths

Case 4: "FORK 15 - 50%" radial system for shortened vertical radiator, 0.125 
wavelengths tall
  15 x 0.0625 wavelength radials
  30 x 0.0625 wavelength radials
  Number of wires: 45 x 0.0625 wavelength
  Maximum conductor spacing: 0.05 wavelength, at the fork junctions and 
outside ends
  Expected efficiency: More than 0.25 dB below conventional 60 radial 
system, but still very good
  Total wire length required: 2.82 wavelengths


In case 3, the savings in wire between the "CONVENTIONAL 60" and the "FORK 
15" schemes is: 15-5.625 = 9.375 wavelengths. For a full-sized 160m 
Vertical, this translates to a savings of about 4,600 feet of wire!

In case 4, with a shortened, loaded vertical of 0.125 wavelengths height, 
the savings in wire between the "CONVENTIONAL 60" (full size vertical) and 
the "FORK 15 - 50%" schemes is: 15-2.82 = 12.18 wavelengths. For a 
full-sized 160m Vertical, this translates to a savings of about 6,000 feet 
of wire!

I will probably try this for a portable vertical project in the future.

Cheers!

--...MARK_N1LO...--



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