Topband: Optimum number of radials for given wire length
Richard (Rick) Karlquist
richard at karlquist.com
Fri Aug 13 09:29:19 PDT 2010
> I have the ARRL's ANTENNA BOOK 20th Edition, and on Chapter 3 (The
> Effects of the Earth), p.3-10 is Table 1 tht maybe contains all you want
> about that.
> If you haven't the book here is the table:
>
> Number of radials 16 24 36 60 90 120
>
> Length of each radial in 0.10 0.125 0.15 0.20 0.25 0.40
> wavelengths
>
> Spacing of radials in degrees 22.5 15 10 6 4 3
>
> Total length of radial wire 1.6 3 5.4 12 22.5 48
> installed in wavelengths
>
> Power loss in dB at low angles 3 2 1.5 1 0.5 0*
>
> with a L/4 radiating element
>
> Feed-point impedance in ohms 52 46 43 40 37 35
> with a L/4 radiating element
>
> * compared to a perfectly conducting ground
>
> 73 Panos SV1GRD
>
The dB loss numbers vs feed point impedance don't make sense to me.
To get 3 dB loss, the feed point impedance should be 70 ohms, not
52 ohms. The dB numbers seem to be off by a factor of 2, IMHO,
like they used 20 LOG instead of 10 LOG.
Also, if your antenna is less than 1/4 wavelength, then of course
the dB loss entries will be considerably different, etc.
Rick N6RK
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