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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