Good Idea Mark: You save wire plus ditching or burial effort which is
equally important (maybe more so). 73, Dan, N5AR
"Mark ." wrote:
>
> 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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