In a ground plane, what dictates the number and spacing of radials?
 

I have seen some with 4 elements, some with 5. Also is the spacing
between them important?

On 10 Jan 2005 08:48:37 -0800, wrote:

I have seen some with 4 elements, some with 5. Also is the spacing
between them important?

The ¼-wave groundplane was developed by George Brown 1938. Here's a
partial quote from his book:

"... In our initial experiments we found that only two horizontal rods
(ground rods) functioned as well as four. Many people from the
Broadcast Sales organization came by to view our tests and they always
expressed doubts as to the ability to radiate uniformly when only two
ground rods were used. To quiet them, we used four ground rods for a
while, thus stilling the criticism. When the antenna became really
popular, we did not dare confess to our ruse."

There you have it from the inventor of the antenna.

73
Danny, K6MHE

"Dan Richardson" wrote in message
...
On 10 Jan 2005 08:48:37 -0800, wrote:

I have seen some with 4 elements, some with 5. Also is the spacing
between them important?

The ¼-wave groundplane was developed by George Brown 1938. Here's a
partial quote from his book:

[deleted]

Interesting... although while I'd certainly believe that, as far as Georbe
Brown could tell in 1938 two radials performed just as well as four radials,
I'd imagine that there is a measurable and simulatable different between the
two systems!

(Hmm... I know... how about... three! ground radials? :-) )

---Joel

In message .com,
writes
I have seen some with 4 elements, some with 5. Also is the spacing
between them important?

A ground plane is an attempt to simulate the earth, with better
conduction, so the more radials the better.

Mike
--
M.J.Powell

M. J. Powell wrote:
In message .com,
writes
I have seen some with 4 elements, some with 5. Also is the spacing
between them important?

A ground plane is an attempt to simulate the earth, with better
conduction, so the more radials the better.

Mike
--
M.J.Powell


Is that a joke?

On another note, why are some of the radials bent to a 45 degree angle
and some are not?

wrote in message
oups.com...
Is that a joke?

No, in most implementations, ground radials are very much attempting to
simulate a solid, perfectly conducting plane under the antenna. Given
enough of them, they do a reasonably good job.

On another note, why are some of the radials bent to a 45 degree angle
and some are not?

As you go to few and fewer radials, the 'pull' of the 'simulated' ground
becomes 'weaker' in a sense and the radiation pattern of an antenna with
horizontal radials tends to have its maximum at an angle significantly above
the horizontal plane. By angling the radials downward, the radiation
pattern is pulled back downward and the maximum radiation is again more or
less horizontal.

(If you don't like this 'maybe intuitive to me and not at all to you'
explanation, you can simulate an antenna with radials in, e.g., ezNEC and
see what the actual results are...)

---Joel Kolstad

Interesting... although while I'd certainly believe that, as far as
Georbe Brown could tell in 1938 two radials performed just as well as
four radials, I'd imagine that there is a measurable and simulatable
different between the two systems!

(Hmm... I know... how about... three! ground radials? :-) )


Actually, for decades, I have built and used 3 radial ground plane
antennas for 2M and for 440. I simply used brass welding rods and SO-
239 connectors to construct them. The reason I used 3 radials.... I too
was under the misconception that 4 were best, but I had a slight
difficulty adding the 4th radials to my SO-239s so I stuck with three.
Incidently, I found the best 50 ohm match was made when I bent the
radials down about 45 degrees. They worked extremely well when properly
tuned and stood up to some pretty heavy weather, too.



Ed

Assuming the terminal resistance of a resonant dipole is 72 ohms,
then a ground plane separating the halves of the dipole means the
terminal resistance of each half is 36 ohms. Thus the terminal
resistance of the half-dipole over the ground plane is also 36 ohms.
The terminal resistance of the half dipole operating against the
radials bent down can then be any value between 36 and 72 ohms,
depending on the angle of the bending. If the bending changes the
angle from 90° to 180° the resistance has changed from 36 to 72 ohms.
The terminal resistance will be 50 ohms at some angle in between, and
is usually close to 45°.

Hope this helps in understanding what occurs from bending the radials
downward.

Walt, W2DU

Sorry, fellas, I intended to mention in my previous post that I worked
with Dr. George H. Brown in his antenna lab at the RCA Laboratories in
Princeton, and he took great delight in telling me about the 'ruse'
that Dan, K6MHE,related concerning the ground plane with only two
radials. 'Ya got that right, Dan Boy!

Walt, W2DU