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

[Richard Fry]

Guy:  Below are responses to a few of the statements in your recent post on 
this topic.

>I'll have to counter that the two radial figures in your quoted RCA study 
>are not about defining what goes wrong with minimalist and
miscellaneous downward extrapolation of dense and uniform radial systems.

The purpose of the BL&E experiments was to determine how buried radial 
systems of various configurations affect the performance of monopole 
radiators of various electrical heights.  The measured data in their IRE 
paper speaks for itself.  It shows everyone including ham operators the 
effects of using sparse/short radial systems as well as the benefit of using 
dense/long radial systems.

>Tests for a given frequency need to be done on that frequency.

The BL&E tests were designed to determine the "efficiency" of monopole 
antenna systems, as shown by the groundwave field they produce close enough 
to the monopole so that the effects of frequency and earth conductivity are 
negligible.  The data gathered is applicable to other frequencies for 
antenna systems having the same conductor dimensions in wavelengths.

>Sky wave behavior is ASSUMED to be the same as at the ground. This is risky 
>because of the loss mode presumptions used with the ground based field 
>strength. ...  And that is not a rub on this RCA study. All these studies 
>have this blind spot, as if measurement at the ground is in it's own world 
>and seemingly unrelated to skywave.

Unloaded, uniform cross-section monopoles of all physical heights have close 
to sinusoidal current distribution along their heights, with essentially 
zero current at the top.  For monopoles of 1/4-wave height and less this 
produces an elevation pattern having a relative field equal to the cosine of 
the elevation angle: zero field toward the zenith, and maximum field in the 
horizontal plane.  That pattern shape does not change with the number/length 
of buried radials used with the monopole, or the conductivity of the earth 
around the antenna site.  Therefore the h-plane field measured close to such 
a monopole (as done by BL&E) also leads to knowledge of the radiation at 
angles above the horizontal plane.

>There are just too many grotesque differences as measured on RBN, even 
>after all the various (and rightly pointed out) caveats are dealt with.

RBN is more a measure of skywave propagation conditions than the radiation 
patterns of the antennas used.  About the best that can be done using RBN 
for antenna evaluation is by relative comparison for the same transmitted 
power, modulation, carrier frequency, propagation path, date, and time of 
day.

> More radials is better is no urban myth. Dense and uniform really does 
> work the best. But two askew radials often seems to do orders of magnitude 
> worse than such material as the RCA study would suggest. One 100w station 
> in Minnesota went from barely working and being heard in North Carolina, 
> to working Europe, just by picking up his two 1/4 wave radials off the 
> ground, and folding them back elevated to the feed. The old stuff is 
> simply not accounting for true anecdotes like that.

Two radials of any length, lying on or buried in the ground have high r-f 
loss when used as the r-f ground for a monopole (see the BL&E paper).

The data in that BL&E paper was limited to buried radials, but that doesn't 
mean that the effectiveness of using several symmetrically arranged, 
elevated horizontal wires as a counterpoise (instead of using buried wires) 
was/is unknown.  For example the 1952 textbook RADIO ANTENNA ENGINEERING by 
Edmund Laporte has several pages describing them.  Such systems have been 
installed by a few AM broadcast stations in the US, and their performance is 
equal to that of a monopole of that height using 120 x 1/4-wave buried 
radials.  NEC software shows this, as well.

>I don't know how I would find out the exact methodology of how they laid 
>the radials in the RCA Labs case.

Suggest you download and refer to the BL&E paper at the link I provided for 
it earlier in this thread.

RF