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

Ok, I think I am learning something here. If radials simulate earth,
would using a solid steel plate instead of radials be better?

wrote:
Ok, I think I am learning something here. If radials simulate earth,
would using a solid steel plate instead of radials be better?

OK till it rusted away. Some very fine antennas have used
metal roofs for their ground planes.
--
73, Cecil http://www.qsl.net/w5dxp


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wrote:
Ok, I think I am learning something here. If radials simulate earth,
would using a solid steel plate instead of radials be better?

Depends on how you define "better".

For an elevated antenna, once you get beyond about 3 or 4 radials, the
increamental difference in performance for added radials is such that
you would never notice it in a practical application.

A solid plane has the disadvantages of being heavy, has a much larger
wind loading, and is difficult to "droop" to get closer to 50 Ohms.

You can download the demo version of EZNEC from http://www.eznec.com/
and model a simple vertical with varying numbers of radials and see
for yourself.

--
Jim Pennino

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wrote in message
...
wrote:
Ok, I think I am learning something here. If radials simulate earth,
would using a solid steel plate instead of radials be better?

Depends on how you define "better".

For an elevated antenna, once you get beyond about 3 or 4 radials, the
increamental difference in performance for added radials is such that
you would never notice it in a practical application.

Doesn't it somewhat depend on frequency? I.e., how electrically large those
radials appear to the antenna?

I ask due to having seen how commercial AM radio station antennas are
built -- usually something pushing a dozen radials, often over a wire mesh
as well.

I'm thinking that in the case of a commercial station, they often multiple
phased antennas to try to precisely control their radiation pattern, in
which case have each antenna be 'as ideal as possible' probably helps.

---Joel

Joel Kolstad wrote:
wrote in message
...
wrote:
Ok, I think I am learning something here. If radials simulate earth,
would using a solid steel plate instead of radials be better?

Depends on how you define "better".

For an elevated antenna, once you get beyond about 3 or 4 radials, the
increamental difference in performance for added radials is such that
you would never notice it in a practical application.

Doesn't it somewhat depend on frequency? I.e., how electrically large those
radials appear to the antenna?

I ask due to having seen how commercial AM radio station antennas are
built -- usually something pushing a dozen radials, often over a wire mesh
as well.

I'm thinking that in the case of a commercial station, they often multiple
phased antennas to try to precisely control their radiation pattern, in
which case have each antenna be 'as ideal as possible' probably helps.

---Joel

Notice the words "For an elevated antenna" which presumes you are working
at a frequency where there is no problem with 1/4 wave radials.

For low frequencies, as in AM broadcast and the lower HAM bands, elevated
antennas become impractical and must be ground mounted, which means the
radials are usually buried as well as there may not be enough room
for 1/4 wave radials.

For radials on or in the ground, usually 4 to 8 1/4 wave radials is
good enough.

If space is limited so 1/4 wave radials aren't possible, the number
required goes up.

The ARRL Antenna Handbook has a good discussion on this.

You might also look at http://www.cebik.com/radio.html which has a couple
of articles about radials, buried and otherwise.

--
Jim Pennino

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