[Antennas] Diminishing Returns

[Ross Primrose]

On 6/4/09 4:52 PM, David C. Hallam wrote:
> To amplify a bit on my radial problem.  I have the usual 1/4 acre city
> lot.  On this lot there are 7 medium size Live Oak trees.  On the lot
> line adjoining my neighbor there are 4 more.  The only place I have to
> put the vertical is an area between the house and the lot line.  This
> area is approximately 95x20.  The antenna is placed approximately 65 ft
> back on this strip.  The radials will have to run in two pie shaped
> wedges about 180 degrees apart.  The maximum I can get at the end of the
> wedge is about 20 ft.
>
>   From the replies I have received, I gather I am wasting my time putting
> radials down.  I have put in two 8 ft ground rods.  I guess I will just
> go with that.  Because of trees and overhead wiring, I can not elevate
> the antenna.  Living in coastal FL I do not want to roof mount anything.
>
> David
> KC2JD/2
>

I think you've drawn the wrong conclusion. Yes, putting radials down in 
your situation will be far from optimal. Put down what radials you can, 
even short ones in the directions that short is all you can run. Will it 
work as well as 120 half wave radials? No, but it'll work a heck of a 
lot better than no radials at all...

Ross AJ4LL
> Merv Stump wrote:
>
>> David, just asking this question may start a religious war.  However, I
>> believe the most efficient use of radial wire occurs when the tips of the
>> radials are about 0.025 wavelengths apart.  For example, on 80 meters a
>> wavelength is about 260 feet.  0.025 X 260 = 6.5, so the tips of your
>> radials should be about 6.5 feet apart.  If you use quarter wavelength
>> radials on 80 meters they will be about 65 feet, and thus the diameter of
>> the circle they cover will be 130 feet.  The circumference of this circle
>> will be pi X 130 or approximately 408 feet.  408 divided by 6.5 is 62, so
>> about 60 radials is optimal if they are a quarter wavelength long.
>>
>> This is not to say that adding radials beyond this will not show
>> improvement.  It is to say that if you want to improve on the 60 quarter
>> wave radial system, you are better served to begin making the radials
>> longer. Notice that if you follow the above logic and go for one-half
>> wavelength radials you end up with about 120 radials.
>>
>> So your first statement is correct.  You can't have too many, and more and
>> longer is always better.  However, for a fixed amount of wire there does
>> appear to be an optimum tradeoff between length and density.
>>
>> Regards, Merv W2OE
>>
>>
>>
>>
>>
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