On 8/3/2013 3:01 PM, John wrote:
Radials really only apply to quarter-wave verticals. The reason is
that the radials allow the field to act as though is is a half wave
antenna, although the bottom half is virtual.
FALSE! There's a discussion of this in the ON4UN book. Yes, a radial
system performs in the important function of a low loss counterpoise,
but it also serves to shield the fields created by the antenna from the
lossy earth. As it happens, I've recently done extensive NEC modeling on
this. Radial systems DO improve the efficiency of half-wave verticals.
The improvement is not a lot, and is greatest with poor soil (0.5 - 1.2
dB at low angles, 2 - 4 dB at high angles). Also, half-wave verticals
have the virtue of putting more radiation at low angles as compared to a
quarter-wave vertical.
It's certainly true that few of us could install a half-wave vertical or
half-wave radials for a 160M antenna, but some of us could for 40M and
above. And I certainly agree with Rick -- when you're contesting, or
trying to work the weak ones, a couple of dB makes a difference. AND --
a dB or two here, and a dB or two there all add up.
73, Jim K9YC
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