Topband: Optimum number of radials for given wire length

[Richard (Rick) Karlquist]

> 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