[TenTec] Vertical radial question

[Lee A Crocker]

I find this chart most useful in determining the point
of diminishing returns for a given radial system. 

Table 9-1 is from ON4UN's book and reads as follows:

Table 9-1 
Equivalent Resistances of Buried Radial Systems 
Radial 	Number of Radials 
Length   2 	15 	30 	60 	120 
0.15    28.6 	15.3 	14.8 	11.6 	11.6    
0.20 	28.4 	15.3 	13.4 	9.1 	9.1
0.25 	28.1 	15.1 	12.2 	7.9 	6.9     
0.30 	27.7 	14.5 	10.7 	6.6 	5.2 
0.35 	27.5 	13.9 	9.8 	5.6 	2.8 
0.40 	27.0 	13.1 	7.2 	5.2 	0.1 

Across the table is increasing number of radials and
down the table is increasing radial length in
wavelength (i.e .25 is 1/4 wavelength)

>From the chart it is easy to see that for short
radials increasing numbers buys you no increase in
efficiency.  However there is a significant difference
between planting 15 radials and 120 in terms of work
and expense.  15 radials is a nice afternoon in the
back yard, 120 radials is a project.  For this
questioner the band of interest and hence the
wavelength was not specified so its hard to make a
recommendation, but with the chart one can do the
analysis for one's self.

The difference in efficiency between 15 .15 radials
and 120 .15 radials  is .3 dB for a standard 1/4 wave
vertical.  I think the .05 or .025 rule is a good one
for 1/4 wave or longer radials but I think it is over
kill for short radials.

Efficiency = Rad Res/(Rad Res + Ohmic loss)

73  W9OY

 


 
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