Alan,
LB Cebik and UN4UN (Low Band DXing) had some information on using tuned
radials - this is a situation that is covered under the topic of 'raised
radials'. The tuning technique is to tune each radial with the vertical
monopole separately - tune for reactance (X) = zero which is the
resonant condition without respect to the actual SWR or resistance
part. Tune each radial in turn (one at a time), and when all have been
tuned, connect them all together to form the 'ground plane'. After that
resonance tuning is complete, one can design a matching network to match
the resistive portion of the feedpoint to the feedline characteristic
impedance for best power transfer.
The conditions found by someone else in his particular situation may or
may not be applicable to the situation that your antenna exists in.
73,
Don W3FPR
Alan Bloom wrote:
N6LF has done some wonderful experimental work on vertical antennas.
He found that a radial laid on the ground experiences a velocity factor
similar to coax cable. A quarter wavelength is only about 60% of its
free space value. If you make the radials a physical quarter wavelength
long, they are actually closer to a half-wave electrical length
(anti-resonant).
With 4 radials he actually got about a 3 dB improvement by making them
SHORTER!
For my next vertical I will definitely plan to tune the radials. I
think I'll try laying out a 1/2-wave dipole on the ground and then trim
it to resonance. Then cut all the radials to equal the length of one
half of the dipole.
Al N1AL
On Tue, 2008-11-04 at 19:10, Ken Kopp wrote:
Of potential interest to those who use verticals with their Elecraft
rigs.
http://www.antennasbyn6lf.com/
73! Ken Kopp - K0PP
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