Gord, VE6SV, wondered:
> There seems to be an axiom that four (4) raised radials
> equals 120 buried ones.
> Is this true in your experience ?
Nope, not at all in a usual installation. Why?
Because the elevated radials are supposed to be
resonant, or nearly so. This means they have
very high electrical field strength near the far ends
of each radial. If the elevated radials are not very
high from the ground, that high E field out there
couples directly to the ground (simple electric field
lines). Where each field line hits the ground, current
is induced; as the rf potential of the E field varies
with frequency, that current flows in the ground loss;
that uses up some transmitter power which cannot
then be part of the radiated field. Result, loss!
If your soil is very high conductivity, as perhaps at
the beach which is damp and a lot of salt content,
then not much of a problem. But for most of us........
Best to do the radials the "classic" way: lots of them,
at least 36 to 60 on/in the ground (only lose, perhaps a
couple of dB). If you put out the classic 120 or so, then
you will pick up those last couple dB lost (and don't have
them at resonant lengths!!)
Number of radials down vs. signal saved will vary
with the soil conditions, etc.
BTW, the "gain" over the loss from no radials
to 120 radials is said to be around 6 db, per many
measured set ups at broadcast stations, and
commercial HF SW stations.
Out here WWVH did not recover all of their potential
field strength far to the West in the Pacific until they
had 100+ radials out under all of their vertical
radiators even near the beach here on Kauai.
Food for thought. I once had 9 verticals out here
with only four elevated radials for each one: all nine
HF bands, 160 through 10 meters!
None of them worked worth beans!! All gone now, hi.
73, Jim KH7M
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather
Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
and ask for Sherman, W2FLA.
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