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bbradburry(at)allvantage. Guest
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Posted: Tue Feb 06, 2007 5:35 am Post subject: Antenna Polarity?? |
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I have a wing-tip VOR antenna in my plane similar to the one illustrated
in figure 13-12 on page 13-16 of "The Connection".
I can not see up inside the wing well enough to determine which 4-40
screw is attached to the lower part and which screw is attached to the
upper plate.
I am using ring terminals to attach the coax as is shown in the
illustration.
My question: Does the antenna have polarity and does it matter which
screw gets the center conductor and which gets the shield?
If it matters, I will try and see up in there with a dental mirror. I
would also welcome any ideas, techniques, etc., to make the determination.
I have discovered that working through an access opening, with my arm
over the top of nutplates, is not the best part of building an
airplane..{:>)
Thanks for all your assistance.
Bill B
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sportav8r(at)gmail.com Guest
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Posted: Tue Feb 06, 2007 6:00 am Post subject: Antenna Polarity?? |
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I forget whether the gamma match is DC grounded in that design, but if
it isn't, a simple continuity check between coax center and ground,
and coax shield and ground would tell you which way it's wired to the
antenna. Does that make sense?
-the other Bill B
On 2/6/07, Bill Bradburry <bbradburry(at)allvantage.com> wrote:
Quote: |
I have a wing-tip VOR antenna in my plane similar to the one illustrated
in figure 13-12 on page 13-16 of "The Connection".
I can not see up inside the wing well enough to determine which 4-40
screw is attached to the lower part and which screw is attached to the
upper plate.
I am using ring terminals to attach the coax as is shown in the
illustration.
My question: Does the antenna have polarity and does it matter which
screw gets the center conductor and which gets the shield?
If it matters, I will try and see up in there with a dental mirror. I
would also welcome any ideas, techniques, etc., to make the determination.
I have discovered that working through an access opening, with my arm
over the top of nutplates, is not the best part of building an
airplane..{:>)
Thanks for all your assistance.
Bill B
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nuckollsr(at)cox.net Guest
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Posted: Tue Feb 06, 2007 6:45 am Post subject: Antenna Polarity?? |
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At 08:37 AM 2/6/2007 -0500, you wrote:
Quote: |
<bbradburry(at)allvantage.com>
I have a wing-tip VOR antenna in my plane similar to the one illustrated
in figure 13-12 on page 13-16 of "The Connection".
I can not see up inside the wing well enough to determine which 4-40 screw
is attached to the lower part and which screw is attached to the upper plate.
I am using ring terminals to attach the coax as is shown in the illustration.
My question: Does the antenna have polarity and does it matter which
screw gets the center conductor and which gets the shield?
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Yes.
Quote: | If it matters, I will try and see up in there with a dental mirror. I
would also welcome any ideas, techniques, etc., to make the determination.
I have discovered that working through an access opening, with my arm over
the top of nutplates, is not the best part of building an airplane..{:>)
|
You can put an antenna analyzer on the end of the coax
and see what it's characteristics look like. If the
coax terminations are reversed, the antenna's swr
will be exceedingly poor . . .
Bob . . .
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nuckollsr(at)cox.net Guest
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Posted: Tue Feb 06, 2007 6:47 am Post subject: Antenna Polarity?? |
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At 08:59 AM 2/6/2007 -0500, you wrote:
Quote: |
I forget whether the gamma match is DC grounded in that design, but if
it isn't, a simple continuity check between coax center and ground,
and coax shield and ground would tell you which way it's wired to the
antenna. Does that make sense?
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Hmmmm . . . good point! I blew that one. Do a continuity
check between the coax center conductor and the AIRFRAME.
If properly connected, the coax will show NO continuity
from center conductor and airframe and good continuity
between the coax shield and airframe.
Thanks Bill.
Bob . . .
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bbradburry(at)allvantage. Guest
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Posted: Tue Feb 06, 2007 3:31 pm Post subject: Antenna Polarity?? |
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Hmmm...I don't think that I made myself clear. This antenna is glassed
in the end of the fiberglas wing. It is not connected to anything.
From the antenna's perspective, it is floating in space. I am
attempting to attach the coax to the antenna. All I have available are
the two screws sticking up to attach the coax. Is there any way that I
can determine which of the two screws should have the center conductor
and which should have the shield?
I can barely get my hand up in there to attach the coax and can not see
what I am touching. Is there any way to test the antenna short of an
SWR meter?
Boll B
Subject: Re: Antenna Polarity??
From: Robert L. Nuckolls, III (nuckollsr(at)cox.net)
Date: Tue Feb 06 - 6:47 AM
At 08:59 AM 2/6/2007 -0500, you wrote:
>
>I forget whether the gamma match is DC grounded in that design, but if
>it isn't, a simple continuity check between coax center and ground,
>and coax shield and ground would tell you which way it's wired to the
>antenna. Does that make sense?
Hmmmm . . . good point! I blew that one. Do a continuity
check between the coax center conductor and the AIRFRAME.
If properly connected, the coax will show NO continuity
from center conductor and airframe and good continuity
between the coax shield and airframe.
Thanks Bill.
Bob . . .
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N6030X(at)DaveMorris.com Guest
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Posted: Tue Feb 06, 2007 3:50 pm Post subject: Antenna Polarity?? |
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Is this a dipole antenna, or what? Does it have a balun? Copper
tape buried in epoxy?
Dave Morris
At 05:33 PM 2/6/2007, you wrote:
Quote: |
<bbradburry(at)allvantage.com>
Hmmm...I don't think that I made myself clear. This antenna is
glassed in the end of the fiberglas wing. It is not connected to
anything. From the antenna's perspective, it is floating in
space. I am attempting to attach the coax to the antenna. All I
have available are the two screws sticking up to attach the
coax. Is there any way that I can determine which of the two screws
should have the center conductor and which should have the shield?
I can barely get my hand up in there to attach the coax and can not
see what I am touching. Is there any way to test the antenna short
of an SWR meter?
Boll B
Subject: Re: Antenna Polarity??
From: Robert L. Nuckolls, III (nuckollsr(at)cox.net)
Date: Tue Feb 06 - 6:47 AM
At 08:59 AM 2/6/2007 -0500, you wrote:
>
>I forget whether the gamma match is DC grounded in that design, but if
>it isn't, a simple continuity check between coax center and ground,
>and coax shield and ground would tell you which way it's wired to the
>antenna. Does that make sense?
Hmmmm . . . good point! I blew that one. Do a continuity
check between the coax center conductor and the AIRFRAME.
If properly connected, the coax will show NO continuity
from center conductor and airframe and good continuity
between the coax shield and airframe.
Thanks Bill.
Bob . . .
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nuckollsr(at)cox.net Guest
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Posted: Tue Feb 06, 2007 4:28 pm Post subject: Antenna Polarity?? |
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At 06:33 PM 2/6/2007 -0500, you wrote:
Quote: |
<bbradburry(at)allvantage.com>
Hmmm...I don't think that I made myself clear. This antenna is glassed in
the end of the fiberglas wing. It is not connected to anything. From the
antenna's perspective, it is floating in space. I am attempting to attach
the coax to the antenna. All I have available are the two screws sticking
up to attach the coax. Is there any way that I can determine which of the
two screws should have the center conductor and which should have the shield?
|
Hmmmm . . . that antenna was designed to work against
metalic structure of a metal wing for "ground". Is there
even a metal sheet over the tip closeout rib? If there's
no metal used to provide the other "half" of the antenna,
then you're going to realize only a small fraction of
the antenna's already compromised performance by tucking
it under a tip fairing?
How did this particular antenna find its way onto the
airplane? It was originally designed for RVs and could
probably be adapted to other metal wing aircraft with
plastic tip fairings.
Bob . . .
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bbradburry(at)allvantage. Guest
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Posted: Thu Feb 08, 2007 5:41 am Post subject: Antenna Polarity?? |
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OK, here is an update...
This plane is a Lancair Legacy, so I got in touch with the Lancair
avionics department. They were able to help me to the point where I was
able to determine which on the two screws should be attached to the
center conductor and which to the shield. So, initial polarization
question/problem solved.
However,...
I noticed in their parts catalog that this antenna is designed (as Bob
remarked) for install in a metal aircraft (Vans RV ??)
However,...
This antenna was glassed in by the Lancair factory when the wing parts
were built, so it was provided by Lancair???? DUH! WHY??
The avionics guy I talked with assured me that the antenna works fine in
the Legacy....
I assume that if I can figure out some way to get the SWR checked on the
antenna and if the SWR is below 2.0, it will work ok??
Thanks for the assistance.
Bill B
Time: 04:28:27 PM PST US
From: "Robert L. Nuckolls, III" <nuckollsr(at)cox.net>
Subject: Re: Antenna Polarity??
At 06:33 PM 2/6/2007 -0500, you wrote:
> ><bbradburry(at)allvantage.com>
> >
> >Hmmm...I don't think that I made myself clear. This antenna is
glassed in
> >the end of the fiberglas wing. It is not connected to anything.
From the
> >antenna's perspective, it is floating in space. I am attempting to
attach
> >the coax to the antenna. All I have available are the two screws
sticking
> >up to attach the coax. Is there any way that I can determine which
of the
> >two screws should have the center conductor and which should have
the shield?
Hmmmm . . . that antenna was designed to work against
metalic structure of a metal wing for "ground". Is there
even a metal sheet over the tip closeout rib? If there's
no metal used to provide the other "half" of the antenna,
then you're going to realize only a small fraction of
the antenna's already compromised performance by tucking
it under a tip fairing?
How did this particular antenna find its way onto the
airplane? It was originally designed for RVs and could
probably be adapted to other metal wing aircraft with
plastic tip fairings.
Bob . . .
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N6030X(at)DaveMorris.com Guest
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Posted: Thu Feb 08, 2007 7:04 am Post subject: Antenna Polarity?? |
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I just read something by Bob Archer that said he sold more of his
wingtip antennas to Lancair owners than to any other airplane. The
document is undated (a horrible problem with most Internet documents)
and is here: http://home.hiwaay.net/~sbuc/tvrvbg/Tip6a.doc
Dave Morris
At 07:43 AM 2/8/2007, you wrote:
Quote: |
<bbradburry(at)allvantage.com>
OK, here is an update...
This plane is a Lancair Legacy, so I got in touch with the Lancair
avionics department. They were able to help me to the point where I
was able to determine which on the two screws should be attached to
the center conductor and which to the shield. So, initial
polarization question/problem solved.
However,...
I noticed in their parts catalog that this antenna is designed (as
Bob remarked) for install in a metal aircraft (Vans RV ??)
However,...
This antenna was glassed in by the Lancair factory when the wing
parts were built, so it was provided by Lancair???? DUH! WHY??
The avionics guy I talked with assured me that the antenna works
fine in the Legacy....
I assume that if I can figure out some way to get the SWR checked on
the antenna and if the SWR is below 2.0, it will work ok??
Thanks for the assistance.
Bill B
Time: 04:28:27 PM PST US
From: "Robert L. Nuckolls, III" <nuckollsr(at)cox.net>
Subject: Re: Antenna Polarity??
At 06:33 PM 2/6/2007 -0500, you wrote:
> ><bbradburry(at)allvantage.com>
> >
> >Hmmm...I don't think that I made myself clear. This antenna is glassed in
> >the end of the fiberglas wing. It is not connected to anything. From the
> >antenna's perspective, it is floating in space. I am attempting to attach
> >the coax to the antenna. All I have available are the two screws sticking
> >up to attach the coax. Is there any way that I can determine which of the
> >two screws should have the center conductor and which should
have the shield?
Hmmmm . . . that antenna was designed to work against
metalic structure of a metal wing for "ground". Is there
even a metal sheet over the tip closeout rib? If there's
no metal used to provide the other "half" of the antenna,
then you're going to realize only a small fraction of
the antenna's already compromised performance by tucking
it under a tip fairing?
How did this particular antenna find its way onto the
airplane? It was originally designed for RVs and could
probably be adapted to other metal wing aircraft with
plastic tip fairings.
Bob . . .
|
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mlas(at)cox.net Guest
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Posted: Fri Feb 09, 2007 8:28 am Post subject: Antenna Polarity?? |
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Bill,
I have the same setup in my Lancair Legacy and it works perfectly. I
put a ramp test set on it in the aircraft when I first certified and it
past the db and sqitter test. I do remember that the antenna must be
connected correctly. The connections are not interchangeable.
Mike L
Lancair Legacy
Kitfox IV
TS-11 Iskra
A-320
--
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nuckollsr(at)cox.net Guest
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Posted: Sat Feb 10, 2007 10:27 am Post subject: Antenna Polarity?? |
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At 08:43 AM 2/8/2007 -0500, you wrote:
Quote: |
<bbradburry(at)allvantage.com>
OK, here is an update...
This plane is a Lancair Legacy, so I got in touch with the Lancair
avionics department. They were able to help me to the point where I was
able to determine which on the two screws should be attached to the center
conductor and which to the shield. So, initial polarization
question/problem solved.
However,...
I noticed in their parts catalog that this antenna is designed (as Bob
remarked) for install in a metal aircraft (Vans RV ??)
However,...
This antenna was glassed in by the Lancair factory when the wing parts
were built, so it was provided by Lancair???? DUH! WHY??
The avionics guy I talked with assured me that the antenna works fine in
the Legacy....
I assume that if I can figure out some way to get the SWR checked on the
antenna and if the SWR is below 2.0, it will work ok??
Thanks for the assistance.
|
A wet string will function to some level. Even a measurement
of SWR is an exceedingly subjective measure of antenna performance.
The acid test is fly it.
Pick a handy cruising altitude and tune in stations at various
distances from your location. Do 1 degree/second, 360-degree turns
and note the bearing arcs (directions relative to aircraft yaw
axis) over which you can still hear the station.
Make your judgements from these kinds of tests stacked against
your personal requirements/wishes. Without substantiating data
from similar tests, anecdotes like Lancair's "works fine" are
essentially meaningless.
Bob . . .
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