Hi Tom and all,
I would absolutely series feed the antenna with a large number of
radials on each element. Either buried, on the ground, or in the air
radials are fine as long as you have at least 30 on each vertical.
My 160 meter "four-square" (using 115/230 degree phase shift) has
60 shallow buried radials, and it actually measures over 6 dB up
from a 200 foot tower with 100 200 foot radials.
> I have an 80M elevated (reverse fed) top-loaded GP with 10
> radials that are 15 ft above ground. The antenna "feels" quite
> competitive and will sometimes even beat out my high dipoles
> at 130 ft. I have worked 230 countries on 80M with this antenna
> (322 lifetime total). See my article in JUNE 1994 QST.
Respectfully Tom, we should add some caution.
That system is highly dependent on the grounding of the tower
base and what is above the feed system. Sometimes it will work
OK, sometimes it will be a "dog".
The entire structure is excited, not just the area above the radials.
There are many conditions where the current flowing down from the
feedpoint will cancel some of the radiation from the current flowing
up, and there are many conditions were the tower base (stuck in
the mud) will dissipate a lot of the applied power.
The only system that will work 100% of the time with predictable
performance is a conventional ground.
On 160 meters, my conventional series-fed towers with 60 or more
radials almost always tie or beat a high dipole (300 feet high!) or a
low dipole (150 feet high) at any distance more than a few hundred
miles and that is broadside to the dipole(s)! The ONLY times I've
ever recorded the dipoles being better have been during
geomagnetic storms or at strong sunrise peaks into Australia and
the Pacific. At sunrise peaks, the verticals are already well over 9
into VK, so I care less about the few dB advantage.
I have two 300 foot high dipoles that basically have been
abandoned, because the verticals are so much more reliable. That
was NOT the case when I compared those dipoles to a system
using four elevated radials. In that case, the dipoles often won! If I
had a crummy ground system, I'd be convinced the dipoles were
the "hot ticket".
Also, keep in mind traditional four square feed arrangements
**require** the antenna be **series** fed at the current maxima. If
you feed it off the current maxima, the rule about using odd 1/4 wl
lines no longer works!
You can not shunt feed or voltage feed a traditional 4 square and
expect it to work correctly. It also will be unreliable with a sparse
ground system, since the radials will radiate as well as couple to
each other and everything around them.
The key with any directional array is making it stable, simple, and
reliable. The only system that qualifies (other than vertical dipoles)
is one that is series fed at the current maximum and has a large
number of radials.
73, Tom W8JI
w8ji@contesting.com
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