In message ,
writes



The ideal radial length for ANY ground plane antenna is slightly longer
than 1/4 wavelength, no matter for what frequencey.

Why is this? I would have thought that a 1/4 wave would be best, as it
offers the lowest impedance.








--
Ian

On Wednesday, April 2, 2014 3:04:29 AM UTC-5, Ian Jackson wrote:
I would have thought that a 1/4 wave would be best, as it
offers the lowest impedance.

Doesn't making the radials a bit long and the monopole a bit short raise the feedpoint resistance? Sorta like an OCF dipole?

In message ,
W5DXP writes
On Wednesday, April 2, 2014 3:04:29 AM UTC-5, Ian Jackson wrote:
I would have thought that a 1/4 wave would be best, as it
offers the lowest impedance.

Doesn't making the radials a bit long and the monopole a bit short
raise the feedpoint resistance? Sorta like an OCF dipole?

But won't you have to shorten the antenna a little to maintain
resonance?
--
Ian

On 4/1/2014 12:21 PM, Channel Jumper wrote:
Radials on a elevated antenna only works if the radials are placed at or
near the bottom of the antenna and are arranged at a 45* angle.

Obviously you have not been doing antennas very long. This statement
above is absurd and everyone here who has been making antennas or just
using them for any length of time knows this.

Making this kind of ridiculous statement removes all your credibility.
Do a little research before saying such silly things.


Any other angle and you might as well not have any radials at all!

Again, just wrong and destroys any cred you might have had here.


On a 10 -12 meter antenna, these radials would need to be at least 1/4
of a wavelength long - 9 feet and preferably 18 feet long to do any
good!

1/4 wavelength works just fine. Longer does not help.


If you coil them up they do not work as intended, but they might help a
little.

Forget calling them a ground plane, think of them more like a mirror.

If you shine a beam of light directly at a mirror, the light is 100%
reflected back towards the source.

Electromagnetic energy is not the same as light. Look that up.


If most of your radiated power is located at the bottom of the antenna
and you can reflect that power up and forward - it is going to radiate
better then something that is only partially effective.

Anything that you don't reflect is adsorbed into the ground - good for
keeping the worms warm at night, but not good for radiating RF..

Only a fool would become a ham and then move into an apartment!

Look who is calling someone a fool.

The sad truth is that most people do not understand what being a ham is
all about anymore and most people thinks that amateur radio is a right
and not a privilege.

Keep trying to understand what being a ham is supposed to be. You might
get there.

Trying to be a ham while living in an apartment building would be like
trying to be a Ocean liner captain while living in Oklahoma...

Some hams are forced into an apartment by economic forces. They can
still be a ham and operate. Your analogy sucks.

The metal railing is much too small in rf area to be an effective
counter poise - sorry but who ever told you this should go back to
school and get a real education.




You would not know anyway.

Ian Jackson wrote:
In message ,
writes



The ideal radial length for ANY ground plane antenna is slightly longer
than 1/4 wavelength, no matter for what frequencey.

Why is this? I would have thought that a 1/4 wave would be best, as it
offers the lowest impedance.

First you have to define what "best" means.

All antennas are a trade off for impedance, bandwidth, gain and in most
cases physical ability to build the structure.

Changing the radial length will have a small effect on impdedance and resonant
point but changing the radial angle will have a bigger effect on impedance
and a very small effect on resonant point.

I would suggest downloading the demo version of EZNEC and modeling a GP to
see what small changes in various parameters do.



--
Jim Pennino

In message ,
writes
Ian Jackson wrote:
In message ,
writes



The ideal radial length for ANY ground plane antenna is slightly longer
than 1/4 wavelength, no matter for what frequencey.

Why is this? I would have thought that a 1/4 wave would be best, as it
offers the lowest impedance.

First you have to define what "best" means.

Yebbut ........
You've just said "the ideal radial length for ANY ground plane antenna
is slightly longer than 1/4 wavelength, no matter for what frequency". I
assumed that "ideal" = "best".
..
All antennas are a trade off for impedance, bandwidth, gain and in most
cases physical ability to build the structure.

Changing the radial length will have a small effect on impdedance and resonant
point but changing the radial angle will have a bigger effect on impedance
and a very small effect on resonant point.

True - but what's the angle of the radials got to do with their length?

I would suggest downloading the demo version of EZNEC and modeling a GP to
see what small changes in various parameters do.

I had presumed you had already do this (or something similar) in order
to say that slightly longer than a 1/4 wavelength was ideal. However, I
have always assumed that the steeper the angle of the radials, the more
the groundplane becomes like a vertical halfwave dipole - and the lower
becomes the angle of radiation.



--
Ian

El 02-04-14 20:25, Ian Jackson escribió:
In message ,
writes
Ian Jackson wrote:
In message ,

writes



The ideal radial length for ANY ground plane antenna is slightly
longer
than 1/4 wavelength, no matter for what frequencey.

Why is this? I would have thought that a 1/4 wave would be best, as it
offers the lowest impedance.

First you have to define what "best" means.

Yebbut ........
You've just said "the ideal radial length for ANY ground plane antenna
is slightly longer than 1/4 wavelength, no matter for what frequency".
I assumed that "ideal" = "best".
.
All antennas are a trade off for impedance, bandwidth, gain and in most
cases physical ability to build the structure.

Changing the radial length will have a small effect on impdedance
and resonant
point but changing the radial angle will have a bigger effect on
impedance
and a very small effect on resonant point.

True - but what's the angle of the radials got to do with their length?

I would suggest downloading the demo version of EZNEC and modeling a
GP to
see what small changes in various parameters do.

I had presumed you had already do this (or something similar) in order
to say that slightly longer than a 1/4 wavelength was ideal. However,
I have always assumed that the steeper the angle of the radials, the
more the groundplane becomes like a vertical halfwave dipole - and the
lower becomes the angle of radiation.

You are right, very steep radials become the lower half of a half wave
dipole as the currents do not cancel eachother and contribute to the
field of the quarter wave monopole. The "ultimate" version is the
sleeve dipole.

When they are in the horizontal plane, the contribution to the total
radiation pattern is very small, and the contribution from the radials
is even zero for the vertically polarized component at zero elevation.

The "somewhat longer then 1/4 wavelength" I also noticed with radials
connected to a coaxial braid to form a narrow band common mode choke.
the choking effect (common mode insertion loss) is better when they
are somewhat longer then 0.25lambda (depending in thickness).

The effect of sloping angle on zero elevation gain is small, and you
get hardly measurable more gain when they are almost vertical. Sloping
radials have some other advantage: less birds.





--
Wim
PA3DJS
Please remove abc first in case of PM

Ian Jackson wrote:
In message ,
writes
Ian Jackson wrote:
In message ,
writes



The ideal radial length for ANY ground plane antenna is slightly longer
than 1/4 wavelength, no matter for what frequencey.

Why is this? I would have thought that a 1/4 wave would be best, as it
offers the lowest impedance.

First you have to define what "best" means.

Yebbut ........
You've just said "the ideal radial length for ANY ground plane antenna
is slightly longer than 1/4 wavelength, no matter for what frequency". I
assumed that "ideal" = "best".

Poor choice of words on my part.

Most of the literature I've seen on the subject recommends radials about
5% longer than the driven element.

I don't recall anyone saying why.

All antennas are a trade off for impedance, bandwidth, gain and in most
cases physical ability to build the structure.

Changing the radial length will have a small effect on impdedance and resonant
point but changing the radial angle will have a bigger effect on impedance
and a very small effect on resonant point.

True - but what's the angle of the radials got to do with their length?

Not a whole lot but they do interact.

I would suggest downloading the demo version of EZNEC and modeling a GP to
see what small changes in various parameters do.

I had presumed you had already do this (or something similar) in order
to say that slightly longer than a 1/4 wavelength was ideal. However, I
have always assumed that the steeper the angle of the radials, the more
the groundplane becomes like a vertical halfwave dipole - and the lower
becomes the angle of radiation.

The angle of radiation in free space for a vertical dipole and a GP no
matter what the radial droop are both 0 degrees.

The thing that changes the angle of radiation is the antenna distance from
ground in wavelengths.



--
Jim Pennino

Wimpie wrote:
El 02-04-14 20:25, Ian Jackson escribió:
In message ,
writes
Ian Jackson wrote:
In message ,

writes



The ideal radial length for ANY ground plane antenna is slightly
longer
than 1/4 wavelength, no matter for what frequencey.

Why is this? I would have thought that a 1/4 wave would be best, as it
offers the lowest impedance.

First you have to define what "best" means.

Yebbut ........
You've just said "the ideal radial length for ANY ground plane antenna
is slightly longer than 1/4 wavelength, no matter for what frequency".
I assumed that "ideal" = "best".
.
All antennas are a trade off for impedance, bandwidth, gain and in most
cases physical ability to build the structure.

Changing the radial length will have a small effect on impdedance
and resonant
point but changing the radial angle will have a bigger effect on
impedance
and a very small effect on resonant point.

True - but what's the angle of the radials got to do with their length?

I would suggest downloading the demo version of EZNEC and modeling a
GP to
see what small changes in various parameters do.

I had presumed you had already do this (or something similar) in order
to say that slightly longer than a 1/4 wavelength was ideal. However,
I have always assumed that the steeper the angle of the radials, the
more the groundplane becomes like a vertical halfwave dipole - and the
lower becomes the angle of radiation.

You are right, very steep radials become the lower half of a half wave
dipole as the currents do not cancel eachother and contribute to the
field of the quarter wave monopole. The "ultimate" version is the
sleeve dipole.

Not really.

When they are in the horizontal plane, the contribution to the total
radiation pattern is very small, and the contribution from the radials
is even zero for the vertically polarized component at zero elevation.

The theoretical gain of a GP with horizontal radials, radials drooping
45 degrees and and drooping 85 degrees is 1.42, 2.22, and 3.67 dbi.

The "somewhat longer then 1/4 wavelength" I also noticed with radials
connected to a coaxial braid to form a narrow band common mode choke.
the choking effect (common mode insertion loss) is better when they
are somewhat longer then 0.25lambda (depending in thickness).

The effect of sloping angle on zero elevation gain is small, and you
get hardly measurable more gain when they are almost vertical. Sloping
radials have some other advantage: less birds.

Changing the angle of the radials has little to no effect on elevation gain
unless the radial ends are a very tiny fraction of a wavelength above ground.

Elevation radiation angle is almost totally determined by the antenna
height above ground.


--
Jim Pennino

In message ,
writes





The theoretical gain of a GP with horizontal radials, radials drooping
45 degrees and and drooping 85 degrees is 1.42, 2.22, and 3.67 dbi.

I would have thought that the 'ultimate' would be when the droop IS 90
degrees (ie essentially a sleeve dipole).

With a droop of 90 degrees, is the gain slightly more than 3.67?

How come that you can have a 1/4 wave radiator groundplane type of
antenna with a gain that is more than a halfwave dipole (2.15 dBi) -even
if it is more-or-less a sleeve dipole?






--
Ian