You must have missed the announcement I posted not long ago. The article
about transmission line phasing systems ("The Simplest Phased Array Feed
System - That Works") is now available at
http://eznec.com/Amateur/Articles/. And there's also a new Windows
Simpfeed program which takes EZNEC (or other modeling program) reported
feedpoint impedances as its input (no mutual Z calculation necessary)
and calculates the feedline lengths necessary for proper phasing. Click
the Simpfeed link at that same URL to get it. It's considerably more
versatile than the older DOS programs. A short manual, including a
detailed example (using both the EZNEC demo and the standard EZNEC
program type), can be viewed by clicking the Help button in the program
window.

EZNEC example files CardTL.EZ and 4SqTL.EZ illustrate the results of
using this feed method. The new program does all calculations in double
precision, so you'll find the values it generates are slightly different
than the values in the example files -- they're actually better.

Roy Lewallen, W7EL

Cecil Moore wrote:
Years ago I experimented with two-element beams where both
elements were driven. Roy, W7EL, has some BASIC programs
on his web page that allows the calculation of phasing
harnesses for such antennas. The disadvantage is that one
must know the mutual coupling impedance between the two
elements.
. . .

Roy Lewallen wrote:
And there's also a new Windows
Simpfeed program which takes EZNEC (or other modeling program) reported
feedpoint impedances as its input (no mutual Z calculation necessary)
and calculates the feedline lengths necessary for proper phasing. Click
the Simpfeed link at that same URL to get it. It's considerably more
versatile than the older DOS programs.

What is the URL for the Windows Simpfeed program link?
I don't see it on your web page. (Do you remember I
sent you a DOS BASIC program about a decade ago that
does that calculation without needing Rm and Xm?)
--
73, Cecil http://www.qsl.net/w5dxp

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Roy Lewallen wrote:
Simpfeed program which takes EZNEC (or other modeling program) reported
feedpoint impedances as its input (no mutual Z calculation necessary)
and calculates the feedline lengths necessary for proper phasing. Click
the Simpfeed link at that same URL to get it.

Sorry, I wasn't reading closely enough and was looking for
it on your web page. I found it.
--
73, Cecil http://www.qsl.net/w5dxp


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i am not clear on how this antenna would look, when i think of 2
elements "" phased or simul driven i presumed it would sorta look like
a typical beam elements in parrallel spaced apart

that being the case , i am not clear on how changing the feedpoint
alters the ew ns direction

unless of course the antenna is like a cross


the gain seemed nice wouldn't mind trying one, my catch is i am using a
sgc tuner to feed my present dipole, i suppose i could just take it's
output and feed both 'elements' be a neet experiment

thanks
m


Years ago I experimented with two-element beams where both
elements were driven. Roy, W7EL, has some BASIC programs
on his web page that allows the calculation of phasing
harnesses for such antennas. The disadvantage is that one
must know the mutual coupling impedance between the two
elements.

In article , Cecil Moore
wrote:

Given that EZNEC will output the feedpoint impedances for
both elements, for a common class of two-element beams,
the mutual coupling impedance can be calculated from the
EZNEC data. Assuming the two-element beam consists of
two identical center-fed elements and assuming that the
feedpoint current magnitudes are equal, one can design
the beam to meet certain specifications, obtain the
feedpoint impedances from EZNEC, and calculate the
mutual coupling to be entered into Roy's BASIC phasing
software.

Lewell1.bas program available as simpfeed.zip on www.eznec.com.

One advantage of a wire beam like this is that the direction
of maximum gain can be reversed by changing the feedpoint
position on the coaxial phasing harness. Good E-W or N-S
beam performance is obtained with one fixed wire beam on the
lower bands.
--
73, Cecil, W5DXP

Cecil Moore, W5DXP wrote:
"Years ago I experimented with two-element beams where both elements
were driven."

J.D. Kraus, inventor of the W8JK beam obviously did too. He found the
most gain he could get is the configuration of the W8JK. Some of his
results are summarized in Table 6-2 on page 192 of the 3rd edition of
"Antennas".Cecil has this book, I believe. Kraus reports the W8JK gain
as 6.1 dBi.

The W8JK has two dipoles spaced at 1/8 wavelength and fed 180-degrees
out of phase. Close coupling causes super gain but a very low drivepoint
resistance. Kraus calculates the drivepoint impedance as 9+j48 ohms on
page 186.

Best regards, Richard Harrison, KB5WZI

Richard Harrison wrote:
Cecil Moore, W5DXP wrote:
"Years ago I experimented with two-element beams where both elements
were driven."

J.D. Kraus, inventor of the W8JK beam obviously did too. He found the
most gain he could get is the configuration of the W8JK. . .

The W8JK doesn't provide the most gain of any two element array of half
wavelength elements for a given spacing. At 0.1 wavelength spacing, a
two element array fed with a 166 degree relative phase angle provides
about 1.4 dB greater gain than a W8JK. At 0.25 wavelength spacing, 142
degree phasing gives the highest gain, just over 1 dB greater than a
W8JK. These phasings also provide a higher feedpoint impedance than the
W8JK, which results in decreased conductor loss and easier matching.

The W8JK has some advantages over other two element arrays, but having
the highest gain isn't one of them.

Roy Lewallen, W7EL

Roy, W7EL wrote:
"The W8JK doesn`t provide thye most gain of any two element array of
half wavelength elements for a given spacing."

The W8JK had the highest gain of the 5 examples compared in the table.

The advantage of EZNEC is shown in Roy`s posting.

Roy also wrote:
"At 0.25 wavelength spacing, 142 degree phasing gives the highest gain,
just over 1 dB greater than a W8JK. These phasings also provide a higher
nfeedpoint impedance than a W8JK,---."

I`d rather have Roy`s antenna.

Best regards, Richard Harrison, KB5WZI

ml wrote:
that being the case , i am not clear on how changing the feedpoint
alters the ew ns direction

Referring to the files I attached yesterday:
If the current in element#2 lags the current in element#1
then you get 12 dBi gain in one direction. If the current
in element#2 leads the current in element#1 then you get
12 dBi gain in the opposite direction. The phasing feedline
might look something like this with coaxial 'T' connectors
installed at points "x" and 'y':

Element#1--------x----------y--------Element#2

Assuming connecting the RF at point 'x' will yield 12 dBi
gain in a Westward direction, connecting the RF at point
'y' will yield 12 dBi gain in an Eastward direction
without moving the elements.
--
73, Cecil, W5DXP

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The method is described briefly in the article posted on my web site.

If someone gives you the self and mutual impedances of two elements and
the lengths of two feedlines connecting them to a common point, it's a
fairly simple matter to calculate the resulting element currents. What
the program does is work the same problem backward. That is, given the
self and mutual impedances of the elements (or in the case of the new
program, the feedpoint impedances when properly fed), it finds the
feedline lengths which will produce the desired current ratio *in those
two impedances*. Years ago I got interested in the problem and figured
out how to work it in that direction. It involves a bunch of variable
transformations to keep the equation sizes reasonable, and results in a
nice, closed-form solution. Some time after I came up with the method, I
spotted an article in Ham Radio magazine which described a solution
using an iterative approach -- it solved the problem in the easy
direction, looked at the result, modified the feedline lengths, tried
again, and so forth. That works (I had done it that way before figuring
out the closed form solution), but can be time consuming -- at least it
could with the computers of the time --, and you have to be careful with
the algorithm to keep the process stable.

I wrote to the author of the Ham Radio article telling him of my method,
and he suggested that I write it up. I had just gone through a lengthy
period of very unpleasant dealings with magazines and editors
(particularly Rich Rosen at Ham Radio), and had no interest in having
more of it. So he ended up writing the paper describing the method in
step-by-step fashion. You can find it in "A Voltage-Matching Method for
Feeding Two-Tower Arrays" by A. Christman, in IEEE Trans. on
Broadcasting, June 1987. Or if you're a masochist, you can try
untangling the GWBASIC spaghetti code in the original DOS programs.

Roy Lewallen, W7EL

Cecil Moore wrote:
Roy Lewallen wrote:

These phasings also provide a higher feedpoint impedance than the
W8JK, which results in decreased conductor loss and easier matching.


Where your simpfeed method really makes sense is with beams
where the elements are more than 1/2WL long. For instance,
attached is the 33 ft. long, two-driven-elements spaced at
ten feet used on 17m. The impedances are high enough to use
300 ohm twinlead for the phasing and the feedpoint impedance
at the phasing harness is around 25 ohms.

Roy, what is the secret to balancing those currents in the
two elements? With the same Z0 phasing lines, the SWR circles
don't intersect so the impedances looking into those phasing
lines is never equal. Does my question make sense?
--
73, Cecil, W5DXP

There are a couple of distinct advantages of the W8JK over the antennas
I described. One is that it can be fed with two equal lengths of
transmission line to the elements, one being given a physical half twist
to effect the phase reversal. Then you have an antenna whose properties
remain the same over an extremely wide bandwidth. The second is that the
free-space pattern consists of two relatively narrow lobes in the
vertical plane, with an overhead null. This results in a concentration
of radiation at lower angles than you'll get with a typical Yagi or most
other two element horizontal antennas.

The tradeoffs are that because of the bidirectional pattern, half the
radiation doesn't do you any good; there's no front-back ratio (although
it's also poor on the maximum-gain antennas I described); and loss has
to be managed and can potentially be a problem because of the low
feedpoint impedances.

There's no single perfect antenna -- you pays your money and you makes
your choice. As Richard Heinlein so succinctly said, TANSTAAFL.

Roy Lewallen, W7EL

Richard Harrison wrote:
Roy, W7EL wrote:
"The W8JK doesn`t provide thye most gain of any two element array of
half wavelength elements for a given spacing."

The W8JK had the highest gain of the 5 examples compared in the table.

The advantage of EZNEC is shown in Roy`s posting.

Roy also wrote:
"At 0.25 wavelength spacing, 142 degree phasing gives the highest gain,
just over 1 dB greater than a W8JK. These phasings also provide a higher
nfeedpoint impedance than a W8JK,---."

I`d rather have Roy`s antenna.

Best regards, Richard Harrison, KB5WZI