AHA - now we have the answer to the problem of narrow yagi lobes.
We are simply using the wrong graph paper to depict the pattern.
I'm sure that with enough planning and dedication, a committee of a few
dozen could come up with a special graph paper, custom-made to your yagi
such that no lobes would seem narrow at all.
In fact, your yagi could become the perfect isotropic radiator.
THAT's the ticket.
For a 'more fun' way to plot yagi lobes, you must use a field strength meter
and a motorcycle and a blonde.

" wrote in message
news:KVI1e.159$Vx1.16@attbi_s01...
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.

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

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.
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