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.

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

Utter nonsense.

The radials do have to be at or near the bottom but the angle of the radials
mostly determines the antenna impedance.

With the radials at 90 degrees the impedance will be around 40 Ohms and
at 45 degees very close to 50 Ohms.

One can download the demo version of EZNEC and observe the effect of
radial angle for themselves.

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!

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

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

If you coil them up, you are inductively loading them, shortening the
physical length just like a loaded vertical.

If you make them electrically around 1/4 wavelength, loaded radials will work
just fine.

Ground plane antennas have been made with 4 hamsticks; 1 for the vertical
element and 3 for the radials and they work.

They major drawback to such is the limited bandwidth of loaded antennas.


snip remaining babbling nonsense



--
Jim Pennino

wrote:
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.

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

Utter nonsense.

The radials do have to be at or near the bottom but the angle of the radials
mostly determines the antenna impedance.

With the radials at 90 degrees the impedance will be around 40 Ohms and
at 45 degees very close to 50 Ohms.

One can download the demo version of EZNEC and observe the effect of
radial angle for themselves.

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!

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

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

If you coil them up, you are inductively loading them, shortening the
physical length just like a loaded vertical.

If you make them electrically around 1/4 wavelength, loaded radials will work
just fine.

Ground plane antennas have been made with 4 hamsticks; 1 for the vertical
element and 3 for the radials and they work.

They major drawback to such is the limited bandwidth of loaded antennas.


snip remaining babbling nonsense


Slight correction:

At 90 degrees the impedance will be close to 20 Ohms and at 30 degrees
close to 40 Ohms if not very close to the ground.

It would help if you were to specify what band or bands you are interested
in and how hight this balcony is off the ground.



--
Jim Pennino

El 01-04-14 21:33, escribió:
wrote:
Channel 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.

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

Utter nonsense.

The radials do have to be at or near the bottom but the angle of the radials
mostly determines the antenna impedance.

With the radials at 90 degrees the impedance will be around 40 Ohms and
at 45 degees very close to 50 Ohms.

One can download the demo version of EZNEC and observe the effect of
radial angle for themselves.

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!

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

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

If you coil them up, you are inductively loading them, shortening the
physical length just like a loaded vertical.

If you make them electrically around 1/4 wavelength, loaded radials will work
just fine.

Ground plane antennas have been made with 4 hamsticks; 1 for the vertical
element and 3 for the radials and they work.

They major drawback to such is the limited bandwidth of loaded antennas.


snip remaining babbling nonsense


Slight correction:

At 90 degrees the impedance will be close to 20 Ohms and at 30 degrees
close to 40 Ohms if not very close to the ground.

Jim, nice detail! Many reference say 35 Ohms (as they assume an
infinite ground plane), but it is really as low as you stated.

For JOTA oparation we used a 6 elevated radials arrangement at 40 m
band and I had to extend the radiator to get 50 Ohms. Just adding a
tuning capacitor "removed" the inductive component. Now we have the
means to erect a half wave giving sligtly lower main beam elevation,
and we use 3 radials now.


It would help if you were to specify what band or bands you are interested
in and how hight this balcony is off the ground.





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

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

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

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