Showing my ignorance (or perhaps deteriorating intellect?) again:

I am attempting to compare the gain of a full size (1/4 wave) vertical
to various shorter verticals at 160 meters.

I am looking at the gain in dbi on the 2D plot. I see 1.39 dbi for the
full 1/4 wave and I see 1.52 dbi for the 28 foot version.

I don't believe the shorter antenna has less gain. Where am I going
wrong?
de W8CCW
John Ferrell W8CCW

On Thu, 20 Apr 2006 17:51:02 GMT, John Ferrell
wrote:

I am looking at the gain in dbi on the 2D plot. I see 1.39 dbi for the
full 1/4 wave and I see 1.52 dbi for the 28 foot version.

I don't believe the shorter antenna has less gain. Where am I going
wrong?

Hi John,

Well, at a minumum, your statements conflict from one paragraph to the
next. That is one indication of something wrong even before we
consider the numbers.

Unravelling that knot, and taking only the first paragraph, yes that
looks wrong (in comparison) too. On the third hand, even if it were
true 0.13dB is something you will never measure accurately in your
lifetime. Even more, you would never perceive it.

Your question should be more of the nature, "how did I misread the
results?" to which we could respond to the tenor of your opening
statement:
Showing my ignorance (or perhaps deteriorating intellect?) again

Perhaps if you were to explain how you got here instead (the problem)
of what you found (the symptom).

73's
Richard Clark, KB7QHC

"John Ferrell" wrote:

I am attempting to compare the gain of a full size (1/4 wave) vertical
to various shorter verticals at 160 meters.

I am looking at the gain in dbi on the 2D plot. I see 1.39 dbi for the
full 1/4 wave and I see 1.52 dbi for the 28 foot version.

I don't believe the shorter antenna has less gain. Where am I going
wrong?

Take a look at the phase angle between the feedpoint voltage
and the feedpoint current for the 28 foot version and try to
figure out an efficient matching network. That phase angle
is ~89.95 degrees. The feedpoint voltage is 1400 volts for
only 1.2 watts input. The feedpoint impedance is about
1.2-j1400 ohms.

Try using the helix feature to install a loading coil in the center
of the 28 foot antenna. The gain will drop as expected but the
feedpoint impedance will be easier to match.
--
73, Cecil, W5DXP

Oops! Thanks for the quick response!
That should have read "I can't believe the shorter antenna has MORE
gain". I am not normally troubled by such small differences in db's
but for that small of a gain difference and that large of a physical
difference (104 feet!) I am certain I have missed more than a decimal
point.

The tone of the message was intended as apologetic. I really hate to
bring dumb questions here to the experts but other than my books and
the Internet I have no where else to go with them. I also hate to take
the dumb questions to Roy directly for fear I will wear out my welcome
with him.

On Thu, 20 Apr 2006 10:59:22 -0700, Richard Clark
wrote:

On Thu, 20 Apr 2006 17:51:02 GMT, John Ferrell
wrote:

I am looking at the gain in dbi on the 2D plot. I see 1.39 dbi for the
full 1/4 wave and I see 1.52 dbi for the 28 foot version.

I don't believe the shorter antenna has less gain. Where am I going
wrong?

Hi John,

Well, at a minumum, your statements conflict from one paragraph to the
next. That is one indication of something wrong even before we
consider the numbers.

Unravelling that knot, and taking only the first paragraph, yes that
looks wrong (in comparison) too. On the third hand, even if it were
true 0.13dB is something you will never measure accurately in your
lifetime. Even more, you would never perceive it.

Your question should be more of the nature, "how did I misread the
results?" to which we could respond to the tenor of your opening
statement:
Showing my ignorance (or perhaps deteriorating intellect?) again

Perhaps if you were to explain how you got here instead (the problem)
of what you found (the symptom).

73's
Richard Clark, KB7QHC
John Ferrell W8CCW

I don't find the Helix feature in my copy of EZNEC+ V4.
I believe I can get the same results by inserting an appropriate load.
It will just be a little more cumbersome.

I was not aware that the feeding of the radiator was affected by the
driving source. My "lab models" require a base inductance to get the
radiator into a range I can feed. I have not been including that in
the models.

I added a base inductor of 100uh(r=3) and got the results you
predicted. The 28 foot radiator is now showing -3.75 dbi gain!
Lesson learned!

The matter of the phase angle and the feed point voltage is currently
over my head, I will study it further.

I am using the TLW program from the Antenna Handbook to determine an
appropriate match. I have not tried to verify those calculations with
a lab project YET!

Once again, thank you for the assistance. I was getting pretty
frustrated...
de W8CCW John

On Thu, 20 Apr 2006 18:23:34 GMT, "Cecil Moore"
wrote:



Take a look at the phase angle between the feedpoint voltage
and the feedpoint current for the 28 foot version and try to
figure out an efficient matching network. That phase angle
is ~89.95 degrees. The feedpoint voltage is 1400 volts for
only 1.2 watts input. The feedpoint impedance is about
1.2-j1400 ohms.

Try using the helix feature to install a loading coil in the center
of the 28 foot antenna. The gain will drop as expected but the
feedpoint impedance will be easier to match.
John Ferrell W8CCW

Correction: the base inductor was 75uh
On Thu, 20 Apr 2006 19:06:17 GMT, John Ferrell
wrote:

I don't find the Helix feature in my copy of EZNEC+ V4.
I believe I can get the same results by inserting an appropriate load.
It will just be a little more cumbersome.

I was not aware that the feeding of the radiator was affected by the
driving source. My "lab models" require a base inductance to get the
radiator into a range I can feed. I have not been including that in
the models.

I added a base inductor of 100uh(r=3) and got the results you
predicted. The 28 foot radiator is now showing -3.75 dbi gain!
Lesson learned!

The matter of the phase angle and the feed point voltage is currently
over my head, I will study it further.

I am using the TLW program from the Antenna Handbook to determine an
appropriate match. I have not tried to verify those calculations with
a lab project YET!

Once again, thank you for the assistance. I was getting pretty
frustrated...
de W8CCW John

On Thu, 20 Apr 2006 18:23:34 GMT, "Cecil Moore"
wrote:



Take a look at the phase angle between the feedpoint voltage
and the feedpoint current for the 28 foot version and try to
figure out an efficient matching network. That phase angle
is ~89.95 degrees. The feedpoint voltage is 1400 volts for
only 1.2 watts input. The feedpoint impedance is about
1.2-j1400 ohms.

Try using the helix feature to install a loading coil in the center
of the 28 foot antenna. The gain will drop as expected but the
feedpoint impedance will be easier to match.
John Ferrell W8CCW
John Ferrell W8CCW

"John Ferrell" wrote:
I don't find the Helix feature in my copy of EZNEC+ V4.
I believe I can get the same results by inserting an appropriate load.
It will just be a little more cumbersome.

The helix feature is found under the Wires window under the create
menu. But it is somewhat complicated. A lumped inductance load
will get you started.

The problem with feeding an impedance of 1.2-j1400 ohms is
getting power into the antenna without dissipating most of it
in the matching network.
--
73, Cecil, W5DXP

On Thu, 20 Apr 2006 18:28:33 GMT, John Ferrell
wrote:

Oops! Thanks for the quick response!
That should have read "I can't believe the shorter antenna has MORE
gain". I am not normally troubled by such small differences in db's
but for that small of a gain difference and that large of a physical
difference (104 feet!) I am certain I have missed more than a decimal
point.

Hi John,

Well, this still does not tell us how you got here, only that when you
did you immediately stumbled.

Could it be that you inverted the results too? You know, it would
make more sense as an explanation than anything else.

Besides, if you skip the losses, the two will have such similar gain
figures that no one would be surprised by the razor thin margin of
difference.

73's
Richard Clark, KB7QHC

On Thu, 20 Apr 2006 19:22:17 GMT, "Cecil Moore"
wrote:

"John Ferrell" wrote:
I don't find the Helix feature in my copy of EZNEC+ V4.
I believe I can get the same results by inserting an appropriate load.
It will just be a little more cumbersome.

The helix feature is found under the Wires window under the create
menu. But it is somewhat complicated. A lumped inductance load
will get you started.

The problem with feeding an impedance of 1.2-j1400 ohms is
getting power into the antenna without dissipating most of it
in the matching network.

Not to worry. Ground loss will help with that problem.

If there's no conductor loss in a model, and no ground loss from a
ground system (which can be simulated with a MININEC type ground), the
gain of an infinitesimally short vertical should be about 0.45 dB less
than for a quarter wave vertical. The gains for intermediate lengths
should fall between. The gain difference is caused by the change in
current distribution as the antenna length changes, which in turn causes
a slight change in the pattern shape.

If you're seeing a report of higher gain from the shorter antenna,
something's wrong. Do an Average Gain test to make sure there are no
numerical problems, and also check the segmentation to make sure it's
reasonable. And, of course, make sure that the length is the only
difference between the models.

Roy Lewallen, W7EL

John Ferrell wrote:
Showing my ignorance (or perhaps deteriorating intellect?) again:

I am attempting to compare the gain of a full size (1/4 wave) vertical
to various shorter verticals at 160 meters.

I am looking at the gain in dbi on the 2D plot. I see 1.39 dbi for the
full 1/4 wave and I see 1.52 dbi for the 28 foot version.

I don't believe the shorter antenna has less gain. Where am I going
wrong?
de W8CCW
John Ferrell W8CCW