Angle of radiation
 

On Wed, 13 Dec 2006 07:54:54 -0500, chuck wrote:

I was thinking this particular antenna would have a lower radiation
angle

The quarter-wave ground-plane antenna's vertical radiation pattern
approaches that of a half-wave vertical as the radial droop approaches
90 degrees, while the feedpoint height remains fixed. Whether one views
that as significant is subjective, of course.

Hi Chuck,

Lifting a ground plane off the ground, so that drooping the radials
could, in fact, be drooped; this does more to raise the gain, than
drooping the radials (something like four-fold more).

Already having the antenna off the ground, and then drooping the
radials does accomplish a lowering of the angle, and increasing the
gain. However, I would propose drooping is largely practiced more to
pull the match into 50 Ohms from 35 Ohms than for any perceived
benefit in "Gain" (which is perhaps all of half a dB or slightly
more). Changing the height could easily erode that partial dB.

Moral:
Droop the radials for match;
Raise (correctly place) the antenna for gain.

73's
Richard Clark, KB7QHC

Angle of radiation
 

Richard Clark wrote:
On Wed, 13 Dec 2006 07:54:54 -0500, chuck wrote:

I was thinking this particular antenna would have a lower radiation
angle

The quarter-wave ground-plane antenna's vertical radiation pattern
approaches that of a half-wave vertical as the radial droop approaches
90 degrees, while the feedpoint height remains fixed. Whether one views
that as significant is subjective, of course.

Hi Chuck,

Lifting a ground plane off the ground, so that drooping the radials
could, in fact, be drooped; this does more to raise the gain, than
drooping the radials (something like four-fold more).

Already having the antenna off the ground, and then drooping the
radials does accomplish a lowering of the angle, and increasing the
gain. However, I would propose drooping is largely practiced more to
pull the match into 50 Ohms from 35 Ohms than for any perceived
benefit in "Gain" (which is perhaps all of half a dB or slightly
more). Changing the height could easily erode that partial dB.

Moral:
Droop the radials for match;
Raise (correctly place) the antenna for gain.

73's
Richard Clark, KB7QHC
Richard, you're slipping. A concise helpful response ? Man. I didn't
see that one coming.

and now back to the "tautological vomitorium"

John
AB8O

Angle of radiation
 

Jimmie D wrote:

This afternoon while cleaning a closet I pulled out an old US map that
had been marked with contacts I made back when I worked 10M a lot.
After the local stations there is a big empty area on the map then I
started making contacts again at about 300 miles. Antenna used was a
1/4 lambda groundplane with the radials drooping so to match 50 ohms.
A chart I found indicates that this means I have a vertical angle of
radiation of 50 to 60 degrees. Is this correct??.
. . .

No, it's not. An antenna doesn't have a single angle of radiation, but
radiates at all angles.

Roy Lewallen, W7EL

Angle of radiation
 

"Roy Lewallen" wrote in message
...
Jimmie D wrote:

This afternoon while cleaning a closet I pulled out an old US map that
had been marked with contacts I made back when I worked 10M a lot. After
the local stations there is a big empty area on the map then I started
making contacts again at about 300 miles. Antenna used was a 1/4 lambda
groundplane with the radials drooping so to match 50 ohms. A chart I
found indicates that this means I have a vertical angle of radiation of
50 to 60 degrees. Is this correct??.
. . .

No, it's not. An antenna doesn't have a single angle of radiation, but
radiates at all angles.

Roy Lewallen, W7EL

Thanks Roy, I know but the chart I was using wasnt clear on what it was
presenting. It is a photo copied page out of a book and hopefully there was
more info that went with it than what I have. The chart does seem to be
indicating that one should use the closest skip contacts to get an idea of
the radiation angle. It was my doubts about this that inspired my question.
Perhaps I am taking the chart out of context or maybe it is just wrong..

Jimmie

Angle of radiation
 

"Jimmie D" wrote in message
...
The chart does seem to be
indicating that one should use the closest skip contacts to get an idea of
the radiation angle. It was my doubts about this that inspired my
question.
Perhaps I am taking the chart out of context or maybe it is just wrong..

You shouldn't doubt a chart of things that happened. What you said makes
sense, otherwise. As Cecil said, the radiation leaves your antenna at
(optimum) angles between 9 and 53 degrees. (That's the half-power beamwidth
in an elevation view.)

Low angle radiation, the ground wave, peters out after a few miles, but you
do get local contacts with it. High angle radiation goes into space and is
lost. The mid-angles are refracted in the ionospere and returned to earth.
That's your set of distance range contacts.

Think of how it would be to toss a tennis ball toward a ceiling: If the
ball could go straight up through the ceiling, it would be lost; also, if a
low-angle toss never hit the ceiling, it would also be lost. It's those
mid-length tosses that bring the ball down somewhere in the room that pay
off. I realize this is an imperfect metaphor, but it may do the trick for
you.

"Sal"

Angle of radiation
 

"Sal M. Onella" wrote in message
...

"Jimmie D" wrote in message
...
The chart does seem to be
indicating that one should use the closest skip contacts to get an idea
of
the radiation angle. It was my doubts about this that inspired my
question.
Perhaps I am taking the chart out of context or maybe it is just wrong..

You shouldn't doubt a chart of things that happened. What you said makes
sense, otherwise. As Cecil said, the radiation leaves your antenna at
(optimum) angles between 9 and 53 degrees. (That's the half-power
beamwidth
in an elevation view.)

Low angle radiation, the ground wave, peters out after a few miles, but
you
do get local contacts with it. High angle radiation goes into space and
is
lost. The mid-angles are refracted in the ionospere and returned to
earth.
That's your set of distance range contacts.

Think of how it would be to toss a tennis ball toward a ceiling: If the
ball could go straight up through the ceiling, it would be lost; also, if
a
low-angle toss never hit the ceiling, it would also be lost. It's those
mid-length tosses that bring the ball down somewhere in the room that pay
off. I realize this is an imperfect metaphor, but it may do the trick
for
you.

"Sal"



I dont doubt waht Cecil said but the way this chart is written it would make
you think that you should base the angle of radiation on the closest
contacts that are "skip". I assumed that someone COULD make a chart like
this. I was actually hoping this would be the case because it is much easier
to discern that leading edge than try to pick out some point in the middle.
NOW I dont this this graph wa intended to be used to determine the radiation
angle of any particular antenna. Rather I believe now that it was intended
as an educational tool to get across the relationship between vertical angle
and skip zones.