Topband: Hindering factors in the science of back yard 160m vertical ins

Richard Fry rfry at
Sun Nov 6 02:41:34 PST 2011

Guy Olinger wrote:
>Hams have suffered in the confined circumstances by attempting various
>minimalist extrapolations of commercial radial methodology. The rub is
>that commercial grade research was never done on non-dense,
>non-uniform solutions.

That isn't exactly correct, Guy.

The 1937 real-world experiments of Brown, Lewis & Epstein of RCA Labs 
includes measured data for sets of of radials varying in number from 2 to 
113, and in length from 0.137 to 0.412 lambda.  The paper at shows the 
results for the longer two sets.

>Bell Labs and all the radio pioneer giants have already been there,
>but not for the non-dense non-uniform radial-disadvantaged crowd,
>and not much for skywave.

The results of the BL&E experiments show that for monopole heights ranging 
from about 45º to > 90º using 113 or more symmetrical, buried radials each 
at least 0.412 lambda physical length in free space, the groundwave field 
measured 3/10 mile from the monopole will be within several percent of its 
theoretical maximum value for the same applied power to a perfect monopole 
driven against a perfect ground plane.

In essence this means that the real conductivity of the earth in which that 
number/length of radials is buried has a very little affect on the radiation 
"launched" by that monopole antenna system.

These tests were done at 3 MHz at a site in NJ where earth conductivity was 
not better than 4 mS/m, so they certainly are applicable for 160-m monopole 
systems used by hams.

A good means to test the performance of a monopole antenna system is to 
measure the groundwave field it produces within 1/2 mile or so, and compare 
it to the theroretical value it would have if that power was radiated by 
that system with zero loss in its connection to r-f ground (as per BL&E). 
Doing this accurately takes an expensive, calibrated F.I. meter which few 
hams have, but maybe they could borrow/rent one for a few hours from a local 
AM broadcast station.  The results of the test would show whether they could 
benefit from adding more/longer wires to a given set of less than 120 x 
1/4-wave buried radials.

Rather than be overly concerned about the conductivity of the earth within 
1/2-lambda of a monopole, one could install a "broadcast" type system of 120 
x 1/4-wave buried radials, and be done with it. Such systems using monopoles 
having physical heights of 45º to > 90º will radiate about 95% of the 
applied power, regardless of soil conductivity within the area of the 

Once radiation is launched from a vertical monopole* it is subject to 
whatever real earth conductivity exists beyond the radius of the buried 
radial system.  That will affect both the groundwave and the skywave.

But there isn't much that be done about this, except to move the monopole 
system to a geographical region having better conductivity.

* The shape of the elevation pattern from a given monopole is the same no 
matter what the application.  All unloaded monopole heights up to 5/8 lambda 
radiate (launch) maximum field in the horizontal plane.  Hams may be more 
interested in skywave propagation paths than some Class C AM broadcast 
stations, but that does not mean that a monopole has zero field in the 
horizontal plane and at small elevation angles above it, as sometimes is 
concluded by looking at "far-field" plots produced by NEC software, and 
found in antenna textbooks.


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