What is going on?
 

Many hams have just gone thru an ice storm where many have lost the end
portions of their elements due to the
weight of ice. Strange thing is that many of those hams who suffered damage
are confinced that they see NO difference in their shortened antennas and a
few were adamant that the performance had IMPROVED
One local guru who had many books on radio thought that maybe the real world
was different to what he read in books!
He then took out his ARRL book and right there is said that gain of two
dipoles side by side increases gain in proportion to the spacing between the
ends of the dipole.
Since this revelation was in a book it was obvious that what other hams were
experiencing with their damaged antennas must be true. So the guru purchased
two dipole
and put them side by side and then remove the ends just as the ice storm
would and thus increased the gap between the two dipoles, which the A.R.R.L
BOOK said would produce more gain.
The guru is now befuddled
He listened to experiences in the REAL WORLD and merged it with what must
be right because it was in a BOOK but did not get all this extra gravy he
was looking for !.
What is going on between the real world and what is written in books.?
He He!
Regards
Art

Art, KB9MZ wrote:
"What is going on between the real world and what is written in books?"

Ever heard: "It`s all Greek to me!"?

Prerequisite education is needed to understand books which are likely
accurate. An interpretation may be needed by those lacking the
prerequisites. ARRL books do a pretty good job of simplification for
many hobbiests.

Best regards, Richard Harrison, KB5WZI

" Art Unwin KB9MZ" wrote in message
news:KVAOb.93878$8H.136929@attbi_s03...
Many hams have just gone thru an ice storm where many have lost the end
portions of their elements due to the
weight of ice. Strange thing is that many of those hams who suffered
damage
are confinced that they see NO difference in their shortened antennas and
a
few were adamant that the performance had IMPROVED
One local guru who had many books on radio thought that maybe the real
world
was different to what he read in books!
He then took out his ARRL book and right there is said that gain of two
dipoles side by side increases gain in proportion to the spacing between
the
ends of the dipole.
Since this revelation was in a book it was obvious that what other hams
were
experiencing with their damaged antennas must be true. So the guru
purchased
two dipole
and put them side by side and then remove the ends just as the ice storm
would and thus increased the gap between the two dipoles, which the
A.R.R.L
BOOK said would produce more gain.
The guru is now befuddled
He listened to experiences in the REAL WORLD and merged it with what must
be right because it was in a BOOK but did not get all this extra gravy he
was looking for !.
What is going on between the real world and what is written in books.?
He He!
Regards
Art


ART, I too have lost portions of my antenna due to ice storms, I was able to
retune and still operate my station with the damaged antenna. Howeever ther
is no way I could tell you if it was better or worse as no reference had
benn previously established for comparison. I seriously doubt if those
others that this has happened to had a chance to establish some meaningful
reference either.
I too am familar with the statement reguarding spacing between the ends of
the antenna. I find it both amusing and incredible that anyone could take
this to mean that cutting off the ends of the antenna will cause an increase
in gain.

Jimmy wrote:
"I too am familiar with the statement regarding spacing between the ends
of the antenna."

Yes, The 19th edition of the "ARRL Antenna Book" has Fig 39 on page 8-35
which shows "Gain of two collinear 1/2-WAVE elements as a function of
spacing between the adjacent ends."
It says nothing of cutting off your ends to spite your array!

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.

Best regards, Richard Harrison, KB5WZI

On Fri, 23 Jan 2004 20:36:54 GMT, "Jimmy"
wrote:

ART, I too have lost portions of my antenna due to ice storms, I was able to
retune and still operate my station with the damaged antenna. Howeever ther
is no way I could tell you if it was better or worse as no reference had
benn previously established for comparison. I seriously doubt if those
others that this has happened to had a chance to establish some meaningful
reference either.
I too am familar with the statement reguarding spacing between the ends of
the antenna. I find it both amusing and incredible that anyone could take
this to mean that cutting off the ends of the antenna will cause an increase
in gain.


Hi Jimmy,

Anecdotal evidence is what sells antennas like the eh, even in the
face of their higher efficiency claims resulting in 30dB poorer
signals.

The argument for clipping off "unused" parts of antennas (especially
yagis) is a howler. It is much like a suggestion to paint out the
parts of the telescope lens that you don't look through. Would the
telescope still work? On the boresight perhaps (no field of view, but
with no more magnification for it though), with less light (you can
only use it at local noon), and more fringing (artifacts due to BW
restriction). No doubt there would be someone to offer glowing
testimonial to that advance in science that so confounds the experts.
(And waiting for a Patent publication for special telescope
enhancement paint.)

73's
Richard Clark, KB7QHC

Richard Clark wrote:

On Fri, 23 Jan 2004 20:36:54 GMT, "Jimmy"
wrote:


ART, I too have lost portions of my antenna due to ice storms, I was able to
retune and still operate my station with the damaged antenna. Howeever ther
is no way I could tell you if it was better or worse as no reference had
benn previously established for comparison. I seriously doubt if those
others that this has happened to had a chance to establish some meaningful
reference either.
I too am familar with the statement reguarding spacing between the ends of
the antenna. I find it both amusing and incredible that anyone could take
this to mean that cutting off the ends of the antenna will cause an increase
in gain.



Hi Jimmy,

Anecdotal evidence is what sells antennas like the eh, even in the
face of their higher efficiency claims resulting in 30dB poorer
signals.

The argument for clipping off "unused" parts of antennas (especially
yagis) is a howler. It is much like a suggestion to paint out the
parts of the telescope lens that you don't look through. Would the
telescope still work? On the boresight perhaps (no field of view, but
with no more magnification for it though), with less light (you can
only use it at local noon), and more fringing (artifacts due to BW
restriction). No doubt there would be someone to offer glowing
testimonial to that advance in science that so confounds the experts.
(And waiting for a Patent publication for special telescope
enhancement paint.)

Well Richard, have you not heard of the famous aperture mask? Reduces
the aperture of the telescope, and there are people that swear by them!

And, they don't work either. Your analogy is quite correct.

At best they can improve apparent contrast. But at a reduction in detail.

- Mike KB3EIA -

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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Mike Coslo wrote:
Well Richard, have you not heard of the famous aperture mask?
Reduces the aperture of the telescope, and there are people that swear
by them!

And, they don't work either.

Mine works well to reduce the light from the moon to a comfortable
viewing level for my 18" diameter reflecting mirror.
--
73, Cecil http://www.qsl.net/w5dxp



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On Fri, 30 Jan 2004 08:24:34 -0600, Cecil Moore
wrote:

Mike Coslo wrote:
Well Richard, have you not heard of the famous aperture mask?
Reduces the aperture of the telescope, and there are people that swear
by them!

And, they don't work either.

Mine works well to reduce the light from the moon to a comfortable
viewing level for my 18" diameter reflecting mirror.

So do moonglasses.

Richard Clark wrote:

wrote:
Mine works well to reduce the light from the moon to a comfortable
viewing level for my 18" diameter reflecting mirror.

So do moonglasses.

If you don't mind looking like a dorky nerd. :-)
--
73, Cecil http://www.qsl.net/w5dxp



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