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

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

Roy Lewallen wrote:

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


Robert Anson Heinlein. A master in his field, as you are in yours.

tom
K0TAR

My apology, to the readers and to the late *Robert* Heinlein.

Roy Lewallen, W7EL

Tom Ring wrote:
Roy Lewallen wrote:

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


Robert Anson Heinlein. A master in his field, as you are in yours.

tom
K0TAR

On Tue, 19 Apr 2005 19:17:34 -0700, Roy Lewallen
wrote:

My apology, to the readers and to the late *Robert* Heinlein.

No problem; I'm sure he won't mind.

What would happen if you isolated that second driven element from the boom
(the one you are effecting the phase-shift in, and added another reflector
( naturally it is in proper phase) behind it? Could you get the best of two
worlds? The advantage of the phase-shift plus a FB ratio?

Regards,
John

"Roy Lewallen" wrote in message
...
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

John Smith wrote:
What would happen if you isolated that second driven element from the boom
(the one you are effecting the phase-shift in, and added another reflector
( naturally it is in proper phase) behind it? Could you get the best of two
worlds? The advantage of the phase-shift plus a FB ratio?

That's just the sort of thing antenna modeling programs are for. And
they're good at it.

Roy Lewallen, W7EL

LOL!!! Hmm, I wonder if anyone sells one? grin

Warmest regards,
John

"Roy Lewallen" wrote in message
...
John Smith wrote:
What would happen if you isolated that second driven element from the
boom (the one you are effecting the phase-shift in, and added another
reflector ( naturally it is in proper phase) behind it? Could you get
the best of two worlds? The advantage of the phase-shift plus a FB
ratio?

That's just the sort of thing antenna modeling programs are for. And
they're good at it.

Roy Lewallen, W7EL

Indeed I do sell modeling programs. But it's not necessary to buy one to
answer your question. The EZNEC demo or any of several other free
programs including NEC-2 is adequate.

Roy Lewallen, W7EL

John Smith wrote:
LOL!!! Hmm, I wonder if anyone sells one? grin

Warmest regards,
John

"Roy Lewallen" wrote in message
...

John Smith wrote:

What would happen if you isolated that second driven element from the
boom (the one you are effecting the phase-shift in, and added another
reflector ( naturally it is in proper phase) behind it? Could you get
the best of two worlds? The advantage of the phase-shift plus a FB
ratio?

That's just the sort of thing antenna modeling programs are for. And
they're good at it.

Roy Lewallen, W7EL