The reading I've done says only one radial is required; that the
'favoring' in the direction of the radial is not enough to be worried
about; that there is no cancellation from opposing (or just more)
radials. I have used a single radial ground plane and found this to be
true (at 6' over dirt on 80M). It favors a morning net 800 miles away,
yet worked DX in any other direction easily (then I moved to a rotating
dipole at 60' which beats it out). That ground plane easily beat out a
horizontal dipole I used before them all (fixed, in the 'wrong' angle
because of tree location).
Both the radiator and radial are tuned (equally), but the angle of
difference from dipole to the traditional 90 deg ground plane will cause
the resistance to vary (roughly 72 ohms as a dipole, dropping to ~50
ohms when at 90 degrees), So if another angle is chosen (inverted Y),
to match a 50 ohm feedline (to have a 1:1 SWR), the element lengths are
adjusted equally until that match is made; altering the resonance of the
wires (maximum transfer of energy). And inverted Y antenna would be
between that 50-72 ohm range, still acceptably low SWR to not mess with.
Which again, is not a significant variance, so put it up, try it out and
compare to other antennas. Wire is cheap enough to play with and try
things out.
Modeling will demonstrate the pattern and 'take off' angles quite
clearly; reality is often different because of local objects, ground
resistance, height...
Don't forget to add a common mode current choke at the feed.
73,
Rick NK7I
On 7/26/2020 11:57 AM, Don Wilhelm wrote:
Fred,
That would be correct if they are oriented at 180 degrees from each
other so as to cancel the horizontal radiation. Elevated radials must
be tuned to be effective, but only 2 are needed. How much tuning will
depend on the height above ground.
73,
Don W3FPR
On 7/26/2020 2:36 PM, Fred Jensen wrote:
Ground Plane?
73,
Fred ["Skip"] K6DGW
Sparks NV DM09dn
Washoe County
On 7/25/2020 8:20 PM, kevinr wrote:
An antenna design is stuck in my head. It consists of three
legs, each 1/4 wavelength long. One leg is vertical while the two
radials are 120 degrees below it. The two radials are connected
electrically while the vertical leg is fed separately. If it had
more radials it would be called a 1/4 wave vertical. But the one
stuck in my head has elevated radials and only two of them. I
cannot remember what this antenna is called. I know 'inverted Y
antenna' doesn't work as a search term. Does anyone know what this
is usually called so I can use a better search string? The low take
off angle would be nice. It looks like a 20 or 40 meter version
would be easy to build and raise.
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