Hi Steve,
> I guess when Stew Perry was writing this, there was a lot less readily
> available data on earth systems than there is today. As you say, we
> now know that a radial system does not have to be as big as Stew
> thought (for example, according to some modelling I have seen, a mere
> 30 radials of 20 m in length, spaced around 4 m at their tips, is less
> than 1dB down on a full-size (120-radial) quarter-wave-radius ground
> screen.
We have to be careful with models because they treat the earth as
a homogeneous media, rather that what it really is. I'd rely more on
actual measurements than models if the wires are close to earth.
I admired Stew, he was a wealth of information. Unfortunately most
of the antenna information we all used in the 60's and 70's was
based on anecdotal data that was really quite meaningless, as you
point out below.
> Now the increase in radials should perhaps only have made a dB or less
> difference to ZE7JX's signal. Maybe it was just a coincidence/change
> in conditions that ZE7JX could suddenly work VK6HD... or was it?...
You can safely bet it was because propagation changed. Even from
minute to minute propagation attenuation can change as much as
30 dB or more. From day to day (or night to night) even more.
Even ten dB would get lost in the data clutter unless he was doing
"A-B" tests. The lack of scientific methods and controls is why so
many bad theories become "fact".
73, Tom W8JI
W8JI@contesting.com
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