wrote:
So to the gurus of this group, what actualy creates
the narrowing of the forward lobes ?

The narrowing of the forward lobes is
caused by constructive interference
during superposition of EM waves.
--
73, Cecil http://www.qsl.net/w5dxp


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Yes Cecil I can go along with that otherwise the resultant volume would be
spherical.
What is the scenario that encapsulates this "constructive interference"
event? Is it residual reactance where its underpinning reside?
Art
Art
"Cecil Moore" wrote in message
...
wrote:
So to the gurus of this group, what actualy creates
the narrowing of the forward lobes ?

The narrowing of the forward lobes is
caused by constructive interference
during superposition of EM waves.
--
73, Cecil http://www.qsl.net/w5dxp


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News==----
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Newsgroups
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"Cecil Moore" wrote in message
...
wrote:
So to the gurus of this group, what actualy creates
the narrowing of the forward lobes ?

The narrowing of the forward lobes is
caused by constructive interference
during superposition of EM waves.
--
73, Cecil http://www.qsl.net/w5dxp

Darn - I thought it was pure magic.
Now we hear all about induced currents and interference patterns cancelling
in the rearward and the sides, but constructively interferring in the
forward direction. All in an attempt to become the chosen guru of the
original poster.
If nominated, I will not run - if elected - I will not serve.

Hal I think you are right
It is magic!.
I think that this subject has been pushed to one side during the last
century in the event
anybody should come along and say all is known about antennas
so we can put them in their place.
Someday, someone will come along with an answer and then we can all jump on
him
and ask him to prove it so the monkey is not on our backs.
The post did attract a lot of interest tho even if there was not a cigar
supplied.
It really is amazing what photons can do when they become all entangled.
Time to get back to what SWR really entails when all can put their two
pennies
worth in.
I've got to now draw a circle with a compass and observe how the shape
changes when
replotted with logrithmic and other types of graph paper

Regards
Art

"Hal Rosser" wrote in message
. ..

"Cecil Moore" wrote in message
...
wrote:
So to the gurus of this group, what actualy creates
the narrowing of the forward lobes ?

The narrowing of the forward lobes is
caused by constructive interference
during superposition of EM waves.
--
73, Cecil http://www.qsl.net/w5dxp

Darn - I thought it was pure magic.
Now we hear all about induced currents and interference patterns
cancelling
in the rearward and the sides, but constructively interferring in the
forward direction. All in an attempt to become the chosen guru of the
original poster.
If nominated, I will not run - if elected - I will not serve.

I've got to now draw a circle with a compass and observe how the shape
changes when
replotted with logrithmic and other types of graph paper

Regards
Art

Be sure to give us a report on creating the logarithmic graph paper.
If I heard someone was looking to replot circles on log graph paper, I would
say he must be a ham.
Then I would think about writing a Java program to do it, as I slipped into
sleep while listening to 'Coast-to-coast-AM' on the radio.

Hal
Amateur radio operators have been convinced to display radiation patterns
on logarithmic paper to make it look more directional than normal plotting
procedure.
Since I can now generate a complete circle for an non yagi antenna array
using logarithmic paper on my antenna program I thought it would be
interesting to see
what a circle would look like when using 'standard' graph paper.( a reverse
procedure)
Now, as I write this, I realise that my antenna computor program has the
ability to
make this transition.
This will be interesting as I have no pre-expectations as to what it will
show.
Best regards
Art


"Hal Rosser" wrote in message
. ..
I've got to now draw a circle with a compass and observe how the shape
changes when
replotted with logrithmic and other types of graph paper

Regards
Art

Be sure to give us a report on creating the logarithmic graph paper.
If I heard someone was looking to replot circles on log graph paper, I
would
say he must be a ham.
Then I would think about writing a Java program to do it, as I slipped
into
sleep while listening to 'Coast-to-coast-AM' on the radio.

In message K3B1e.8558$NW5.7100@attbi_s02, "
writes
As gain increases with a yagi design the forward
lobe narrows . With high gain yagi's the lobe
becomes so narrow it is deemed to be a hinderence
instead of an advantage. To overcome this perceived
problem one has to know what causes it.
So to the gurus of this group, what actualy creates
the narrowing of the forward lobes ?
End effects perhaps!

My tuppence worth

It is a fundamental energy conservation effect.

There is an invariant A * Omega , where A is the capture area of the
antenna, proportional to gain and Omega is the solid angle of the lobe.

So as A goes up, Omega must come down.

One way to reduce the effect is to use a number of vertically stacked
low gain yagis. The lobe becomes narrow in the vertical plane , but
remains broad in the horizontal plane. This is fairly common technique
for VHF/UHF contesters, where a narrow horizontal beam can cause missed
contacts

Brian

--
Brian Howie

On Sun, 27 Mar 2005 20:53:27 +0100, Brian Howie
wrote:

One way to reduce the effect is to use a number of vertically stacked
low gain yagis. The lobe becomes narrow in the vertical plane , but
remains broad in the horizontal plane.

Hi Brian,

A simple, but cogent point.

73's
Richard Clark, KB7QHC

One of the old Firestone HF circuits to EL used stacked rhombics to kill the
second lobe. The high angle lobe was hurting RTTY reception because of the
delay associated with receiving via two propagation modes.
Today's modulation methods and computation power would not be hurt by
such multipath propagation.
I have thought of using such a scheme with LPDAs on receiving so as not
to receive US stations so strongly. Most of the hurtful QRM when trying to
work DX comes from first-hop stations. (I am speaking of on-frequency QRM.)
The benefit on transmitting is unimportant.

Lots of fun to use a pair of the 5 element yagis included with EZNEC to
see the effect of vertical (or horizontal) stacking (broadside array).
73, Mac N8TT
--
J. Mc Laughlin; Michigan U.S.A.
Home:

Art Unwin wrote:
"---what actually creates the narrowing of the forward lobes?"

Destructive interference of energy outside the main lobe lobe which
concurrently causes constructive interference within the
forward lobe as energy is neither created nor destroyed but redirected.

Highly conductive parasitic antenna elements can approach 100%
efficiency. They re-radiate, having no load other than a complete highly
conductive short sircuit, nearly all of the energy they intercept.

The re-radiated energy is carefully phased to create the desired
directional pattern. This can be "cut and try" or it can be calculate
and try.

Best regards, Richard Harrison, KB5WZI