[TowerTalk] Why does Cushcraft R7 work so well without radials?
Sun, 11 Mar 2001 11:09:44 -0800 (PST)
The "whiskers" aren't really a ground plane - they create capacitance at
the base of the antenna. If you extended them, then more capacitance
would be present, most likely seriously upsetting the tuning of the
antenna. The capacitance is used to create a feedpoint impedance that is
matchable with the tuning network at that point on the antenna.
The R7-type antennas are fed at relatively high-impedance points, so that
there isn't really a need for a large, low-impedance ground at the
feedpoint. (This is a woefully incomplete description...) This is not to
say that the antennas don't care if there is a good ground in the vicinity
or not. Ground losses are higher with poor ground, regardless.
The R7, R8, etc. do give acceptable performance without an extensive
radial system, but not to the level of a full-size, quarter-wave vertical
over a good ground. This was documented in the K7LXC/N0AX HF vertical
comparative tests conducted last year. (see www.championradio.com if you
want a copy of the report.)
All in all, I was pleasantly surprised at how well the R8 performed,
particularly on 40-meters. I was not surprised at how poorly some of the
other no-radial antennas played, especially on 40/80-meters. Ain't no
free lunch and very few cheap ones.
73, Ward N0AX
> >The Cushcraft R7 and R8 verticals seem to work pretty
> >well. They use 8 "whiskers" that are about 3 feet
> >long as the ground plane. Why does this work so well?
> > Would it work better if the whiskers were real
> >radials? Would making the whiskers twice as long
> >improve the performace?
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