Richard Harrison wrote:
You actually get about 3 dBd gain from two !/2-wave dipoles when there
is a 1/2-wave space between their adjacent ends versus only a 1.5 dBd
gain when there is only the space of a short insulator between the ends
of the 1/2-wave dipoles.

Too bad coils don't have a phase shift through them. :-) If they did,
a phase-reversing coil could be used in that "short insulator space"
to bring the gain back to about 3 dBd as described by Kraus in
_Antennas_for_all_Applications_, vol 3.
--
73, Cecil http://www.qsl.net/w5dxp



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Cecil wrote,

Richard Harrison wrote:
You actually get about 3 dBd gain from two !/2-wave dipoles when there
is a 1/2-wave space between their adjacent ends versus only a 1.5 dBd
gain when there is only the space of a short insulator between the ends
of the 1/2-wave dipoles.

Too bad coils don't have a phase shift through them. :-) If they did,
a phase-reversing coil could be used in that "short insulator space"
to bring the gain back to about 3 dBd as described by Kraus in
_Antennas_for_all_Applications_, vol 3.
--
73, Cecil http://www.qsl.net/w5dxp


What value coil does Kraus recommend, Cecil, for, say, a
pair of forty meter dipoles to make them do what you want
at forty meters?
73,
Tom Donaly, KA6RUH

Tdonaly wrote:
What value coil does Kraus recommend, Cecil, for, say, a
pair of forty meter dipoles to make them do what you want
at forty meters?

It's a textbook, not a cookbook, so he doesn't recommend a
specific "value". The requirement is that the coil be self-
resonant at the operating frequency. Quoting Kraus: "Here the
(1/2WL) elements present a high impedance to the coil which
may be resonated without an external capacitance due to its
distributed capacitance." He says a 2-element array of 1/2WL
elements has a gain of 3.8 dBi, a 3-element array a gain of
5.3 dBi, and a 4-element array a gain of 6.4 dBi.
--
73, Cecil http://www.qsl.net/w5dxp



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Cecil wrote,

Tdonaly wrote:
What value coil does Kraus recommend, Cecil, for, say, a
pair of forty meter dipoles to make them do what you want
at forty meters?

It's a textbook, not a cookbook, so he doesn't recommend a
specific "value". The requirement is that the coil be self-
resonant at the operating frequency. Quoting Kraus: "Here the
(1/2WL) elements present a high impedance to the coil which
may be resonated without an external capacitance due to its
distributed capacitance." He says a 2-element array of 1/2WL
elements has a gain of 3.8 dBi, a 3-element array a gain of
5.3 dBi, and a 4-element array a gain of 6.4 dBi.
--
73, Cecil http://www.qsl.net/w5dxp


So he didn't give an analysis, but just wrote that a self-resonant
coil would do the job. Thanks, Cecil.
73,
Tom Donaly, KA6RUH

Cecil, W5DXP wrote:
"The requirement is that the coil be self-resonant at the operating
frequency."

That`s what I remembered. It`s as if a parallel resonant LC circuit is
substituted for a quarter-wave short-circuited stub inverting the phase.

My problem is finding the page in Kraus` 3rd edition. Anyone have the
number?

Best regards, Richard Harrison, KB5WZI

Richard Harrison wrote:
My problem is finding the page in Kraus` 3rd edition. Anyone have the
number?

Page 824
--
73, Cecil, W5DXP

Cecil, W5DXP wrote:
"Page 824"

Yes. Thank you very much. I had lost track and seemed not to be able to
find the item again.

The illustration is Figure 23-21 (b). Four in-phase 1/2-wave elements
with phase-reversing coils. Kraus says:
"Here the elements present a high impedance to the coil which may be
resonated without an external capacitance due to its distributed
capacitance. A phase reversal is about 180-degrees.

Best regards, Richard Harrison, KB5WZI

Richard Harrison wrote:
Cecil, W5DXP wrote:
"Page 824"

Yes. Thank you very much. I had lost track and seemed not to be able to
find the item again.

Those little sticky tabs solve the problem.

The illustration is Figure 23-21 (b). Four in-phase 1/2-wave elements
with phase-reversing coils. Kraus says:
"Here the elements present a high impedance to the coil which may be
resonated without an external capacitance due to its distributed
capacitance. A phase reversal is about 180-degrees.

Thanks Richard, there are apparently still old wives
who believe that a coil cannot reverse the phase of the current
even though a shorted stub can. I'm going to post the current
magnitudes and phases for a number of 3/2WL configurations along
with the gains.
--
73, Cecil http://www.qsl.net/w5dxp



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