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VHF antenna in the tail
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gilles.thesee(at)free.fr
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PostPosted: Tue Dec 19, 2017 5:41 pm    Post subject: VHF antenna in the tail Reply with quote

Hi all,

My buddy is starting a new ultralight project.
The airframe is carbon fiber (resin infusion) with glass fiber fin to
house a built-in VHF antenna.

On the attached picture of the rear half-fuselage, the glass fin can be
seen, with the carbon fiber tail cone at the base. A small number of
foam ribs will be added.

Question 1 : What would be the lightest and most inexpensive way to
construct an efficient VHF antenna housed in the tail fin ?
Question 2 : Will it be necessary to build a glass fiber rudder, or will
carbon fiber be acceptable (weight concern) ?

Thanks in advance for your inputs, advices, opinions, etc.

--
Best regards,
Gilles
http://contrails.free.fr
http://lapierre.skunkworks.free.fr


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noel.wade(at)gmail.com
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PostPosted: Tue Dec 19, 2017 6:55 pm    Post subject: VHF antenna in the tail Reply with quote

Hi,  
Putting the antenna in the tail is a common technique used in modern Sailplanes (which feature mostly carbon-fiber construction) - either the vertical fin or the rudder is glass. Carbon Fiber won't work at all - it blocks radio waves in the range that we're interested in.
  
Can't speak to exactly how you would best construct it, but you want to look into a Dipole antenna - if you do some Google searching on that you'll find some info (and Aircraft Spruce also sells one for this kind of purpose, for a little over $100). They can be made relatively flat and then bonded (with fiberglass and resin) to the inside of the skin of the tail (again, assuming the skin is fiberglass and thus transparent to VHF radio waves).
  
Good luck,
  
--Noel
  
  


On Tue, Dec 19, 2017 at 5:41 PM, GTH <gilles.thesee(at)free.fr (gilles.thesee(at)free.fr)> wrote:
Quote:
Hi all,

My buddy is starting a new ultralight project.
The airframe is carbon fiber (resin infusion) with glass fiber fin to house a built-in VHF antenna.

On the attached picture of the rear half-fuselage, the glass fin can be seen, with the carbon fiber tail cone at the base. A small number of foam ribs will be added.

Question 1 : What would be the lightest and most inexpensive way to construct an efficient VHF antenna housed in the tail fin ?
Question 2 : Will it be necessary to build a glass fiber rudder, or will carbon fiber be acceptable (weight concern) ?

Thanks in advance for your inputs, advices, opinions, etc.

--
Best regards,
Gilles
http://contrails.free.fr
http://lapierre.skunkworks.free.fr



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ceengland7(at)gmail.com
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PostPosted: Tue Dec 19, 2017 6:55 pm    Post subject: VHF antenna in the tail Reply with quote

On 12/19/2017 7:41 PM, GTH wrote:
Quote:
Hi all,

My buddy is starting a new ultralight project.
The airframe is carbon fiber (resin infusion) with glass fiber fin to
house a built-in VHF antenna.

On the attached picture of the rear half-fuselage, the glass fin can
be seen, with the carbon fiber tail cone at the base. A small number
of foam ribs will be added.

Question 1 : What would be the lightest and most inexpensive way to
construct an efficient VHF antenna housed in the tail fin ?
Question 2 : Will it be necessary to build a glass fiber rudder, or
will carbon fiber be acceptable (weight concern) ?

Thanks in advance for your inputs, advices, opinions, etc.

You can make a quarter wave antenna using copper foil (think back to the

old glass-break stripes on windows before solid state glass break
detectors), but physical strength is virtually zero, and would require
somewhat elaborate measures to protect it from breakage. It also would
need a ground plane, and I wouldn't be confident that a carbon fuselage
could provide it.

Same technique is possible making a dipole, but would require close to 4
feet  of height.

How about this?
http://www.chiefaircraft.com/sa-006.html

A carbon rudder would no doubt affect it, but by how much; who can tell?
The effect might be only measurable on an antenna range with test gear.

---
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henador_titzoff(at)yahoo.
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PostPosted: Tue Dec 19, 2017 7:00 pm    Post subject: VHF antenna in the tail Reply with quote

Gilles,
A dipole antenna is the perfect antenna for VHF comm on a composite airplane. You just cut the VHF antenna to the mid-frequency range. It is a half-wave length long, so cut it to the mid-range wavelength size. Construct the antenna with two copper tape pieces. both totaling the mid-range wavelength. The RF cable should come in at the middle of the two pieces. Center conductor to one tape piece, and shield to the other. I would put the copper tapes at the fin leading edge and have the cable go toward the back and down. You could do it vice-versa, but the rudder hinges may interfere with the RF environment. Try to get the thickest copper tape as thicker makes the antenna more broadband. You can test the antenna before glassing it in with a SWR meter attached to the radio side of the cable. Find an amateur radio person somewhere. Most of them have SWR meters.

I would not recommend a carbon fiber rudder, as it will introduce a conducting surface that will interfere with the antenna.

Henador Titzoff

From: GTH <gilles.thesee(at)free.fr>
To: aeroelectric-list(at)matronics.com
Sent: Tuesday, December 19, 2017 9:05 PM
Subject: VHF antenna in the tail


Hi all,

My buddy is starting a new ultralight project.

The airframe is carbon fiber (resin infusion) with glass fiber fin to

house a built-in VHF antenna.

On the attached picture of the rear half-fuselage, the glass fin can be

seen, with the carbon fiber tail cone at the base. A small number of

foam ribs will be added.

Question 1 : What would be the lightest and most inexpensive way to

construct an efficient VHF antenna housed in the tail fin ?

Question 2 : Will it be necessary to build a glass fiber rudder, or will

carbon fiber be acceptable (weight concern) ?

Thanks in advance for your inputs, advices, opinions, etc.

--

Best regards,

Gilles

http://contrails.free.fr

http://lapierre.skunkworks.free.fr


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glastar(at)gmx.net
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PostPosted: Tue Dec 19, 2017 9:46 pm    Post subject: VHF antenna in the tail Reply with quote

Gilles,

I did use a ADVANCED AIRCRAFT ELECTRONICS, INC. antenna in my Glastar
below the baggage floor as a NAV antenna, as I removed the NAV (8.33
upgrade) it would be available, I'm based in Switzerland. it is a 5T
model and I was very satisfied on its usage, length is about 110 cm.

See:
http://www.advancedaircraft.com/#models

http://www.aircraftspruce.com/catalog/graphics/vhf5dia.jpg

Cheers Werner

On 20.12.2017 02:41, GTH wrote:
Quote:
Hi all,

My buddy is starting a new ultralight project.
The airframe is carbon fiber (resin infusion) with glass fiber fin to
house a built-in VHF antenna.

On the attached picture of the rear half-fuselage, the glass fin can be
seen, with the carbon fiber tail cone at the base. A small number of
foam ribs will be added.

Question 1 : What would be the lightest and most inexpensive way to
construct an efficient VHF antenna housed in the tail fin ?


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user9253



Joined: 28 Mar 2008
Posts: 1263
Location: Riley TWP Michigan

PostPosted: Wed Dec 20, 2017 7:02 am    Post subject: Re: VHF antenna in the tail Reply with quote

Make your own copper tape by flatting #12 AWG solid wire using a hammer and anvil.

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gilles.thesee(at)free.fr
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PostPosted: Wed Dec 20, 2017 7:05 am    Post subject: VHF antenna in the tail Reply with quote

Le 20/12/2017 à 02:41, GTH a écrit :

Quote:

On the attached picture of the rear half-fuselage, the glass fin can be seen, with the carbon fiber tail cone at the base. A small number of foam ribs will be added.

Question 1 : What would be the lightest and most inexpensive way to construct an efficient VHF antenna housed in the tail fin ?
Question 2 : Will it be necessary to build a glass fiber rudder, or will carbon fiber be acceptable (weight concern) ?


Hi all,

Thank you everyone who responded.
The project is a small airplane with the fin about 800 mm high (~950 mm leading edge), so space seems a bit limited for a dipole antenna.
Still looking into any solution.
The idea is to design something mostly DIY for cost reasons, so this seems to rule out off-the-shelf antennas.
Any ideas ?

BTW, what is the influence of the radiating element width/diameter vs selectivity or else ?
Any hard facts on the subject ?

Thanks for any input,


--
Best regards,
Gilles
http://contrails.free.fr
http://lapierre.skunkworks.free.fr


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nuckolls.bob(at)aeroelect
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PostPosted: Wed Dec 20, 2017 7:17 am    Post subject: VHF antenna in the tail Reply with quote

At 07:41 PM 12/19/2017, you wrote:
Quote:
Hi all,

My buddy is starting a new ultralight project.
The airframe is carbon fiber (resin infusion) with glass fiber fin to house a built-in VHF antenna.

On the attached picture of the rear half-fuselage, the glass fin can be seen, with the carbon fiber tail cone at the base. A small number of foam ribs will be added.

Question 1 : What would be the lightest and most inexpensive way to construct an efficient VHF antenna housed in the tail fin ?
Question 2 : Will it be necessary to build a glass fiber rudder, or will carbon fiber be acceptable (weight concern) ?

Thanks in advance for your inputs, advices, opinions, etc.

What does the structure look like ahead of the
tail group? Is there a space behind the seat(s)
but ahead of the tail group that has some
volume?



Bob . . .


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ceengland7(at)gmail.com
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PostPosted: Wed Dec 20, 2017 7:26 am    Post subject: VHF antenna in the tail Reply with quote

On 12/20/2017 9:02 AM, user9253 wrote:
Quote:


Make your own copper tape by flatting #12 AWG solid wire using a hammer and anvil.

--------
Joe Gores

Or, just make it by snipping a 1/2" wide strip from a piece of aluminum

flashing material (~10-15 thousandths" thick). Nothing magic about
copper, for this application.

---
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PostPosted: Wed Dec 20, 2017 7:26 am    Post subject: VHF antenna in the tail Reply with quote

On 12/20/2017 9:17 AM, Robert L. Nuckolls, III wrote:

Quote:
At 07:41 PM 12/19/2017, you wrote:
Quote:
Hi all,

My buddy is starting a new ultralight project.
The airframe is carbon fiber (resin infusion) with glass fiber fin to house a built-in VHF antenna.

On the attached picture of the rear half-fuselage, the glass fin can be seen, with the carbon fiber tail cone at the base. A small number of foam ribs will be added.

Question 1 : What would be the lightest and most inexpensive way to construct an efficient VHF antenna housed in the tail fin ?
Question 2 : Will it be necessary to build a glass fiber rudder, or will carbon fiber be acceptable (weight concern) ?

Thanks in advance for your inputs, advices, opinions, etc.

What does the structure look like ahead of the
tail group? Is there a space behind the seat(s)
but ahead of the tail group that has some
volume?



Bob . . .
carbon fuselage
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PostPosted: Wed Dec 20, 2017 7:44 am    Post subject: VHF antenna in the tail Reply with quote

On 12/20/2017 7:50 AM, GTH wrote:

Quote:
Le 20/12/2017 à 02:41, GTH a écrit :

Quote:

On the attached picture of the rear half-fuselage, the glass fin can be seen, with the carbon fiber tail cone at the base. A small number of foam ribs will be added.

Question 1 : What would be the lightest and most inexpensive way to construct an efficient VHF antenna housed in the tail fin ?
Question 2 : Will it be necessary to build a glass fiber rudder, or will carbon fiber be acceptable (weight concern) ?


Hi all,

Thank you everyone who responded.
The project is a small airplane with the fin about 800 mm high (~950 mm leading edge), so space seems a bit limited for a dipole antenna.
Still looking into any solution.
The idea is to design something mostly DIY for cost reasons, so this seems to rule out off-the-shelf antennas.
Any ideas ?

BTW, what is the influence of the radiating element width/diameter vs selectivity or else ?
Any hard facts on the subject ?

Thanks for any input,


--
Best regards,
Gilles
http://contrails.free.fr
http://lapierre.skunkworks.free.fr
There have been several good articles in Kitplanes Magazine about the subject. Short answer: the skinnier the element; the more selective and 'peaky' the gain will be vs frequency. According to stuff I've seen, 1/2" width strip (thickness not too important) seems to be adequate to reduce selectivity.

The model I linked earlier isn't cheap, but it would probably perform best. Having said that, once the plane is in the air almost anything will 'work' as long as it's got a clear shot at its target.

Since you don't have the height to use a dipole, and there isn't a practical way to have a ground plane for a quarter-wave, have you considered just using an off the shelf 'rubber ducky' that's made for handheld comms? Probably be as cheap as making something, and is already tuned for working without a ground plane. Also rugged enough that you could make some plastic or fiberglass clips in the tail that it could just snap into, making any future maintenance simpler.


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Joined: 28 Mar 2008
Posts: 1263
Location: Riley TWP Michigan

PostPosted: Wed Dec 20, 2017 9:07 am    Post subject: Re: VHF antenna in the tail Reply with quote

Since there is not enough room for a dipole, it seems that a quarter wave is required. Ideally there should be 4 ground plane radials using copper tape. If there is no access to the inside of the tail, then the ground plane radials could be glued to the exterior of the tail. If exterior radials are not desired due to cosmetic concerns, then only one radial could be placed horizontally in the vertical fin-tail cone junction. Not ideal, but might give adequate performance.
Here is a picture of another homemade option. It is very inexpensive using only coax. It should work good enough.


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PostPosted: Wed Dec 20, 2017 1:51 pm    Post subject: VHF antenna in the tail Reply with quote

http://becker-avionics.info/Products/1a005-2/
--


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PostPosted: Wed Dec 20, 2017 1:55 pm    Post subject: VHF antenna in the tail Reply with quote

Most modern gliders have a glass fin to house the radio, transponder and Flarm antennas and some have a carbon rudder, the blanking from the rudder is usually not a factor. You will obtain much better performance buy buying an antenna as you will find it difficult to get a good ground plane.

Peter

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PostPosted: Wed Dec 20, 2017 10:07 pm    Post subject: VHF antenna in the tail Reply with quote

Maybe consider a folded dipole?
I’ll have to consult the ARRL Antenna Book...

Neal George
Sent from my iPhone

On Dec 20, 2017, at 11:07 AM, user9253 <fransew(at)gmail.com> wrote:



Since there is not enough room for a dipole, ...


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PostPosted: Wed Dec 20, 2017 10:14 pm    Post subject: VHF antenna in the tail Reply with quote

As I recall, the characteristic impedance of a folded dipole is 200 ohms, so you would probably need a 1:4 balun to feed it from 50 ohm coax?
Bill

On 21/12/2017 5:06 PM, Neal George wrote:

Quote:
Quote:
--> AeroElectric-List message posted by: Neal George <neal.george(at)gmail.com> (neal.george(at)gmail.com)

Maybe consider a folded dipole?
I’ll have to consult the ARRL Antenna Book...

Neal George
Sent from my iPhone

On Dec 20, 2017, at 11:07 AM, user9253 <fransew(at)gmail.com> (fransew(at)gmail.com) wrote:

--> AeroElectric-List message posted by: "user9253" <fransew(at)gmail.com> (fransew(at)gmail.com)

Since there is not enough room for a dipole, ...



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PostPosted: Wed Dec 20, 2017 10:45 pm    Post subject: VHF antenna in the tail Reply with quote

or is it 300 ohms, so 1:6 balun?

On 21/12/2017 5:14 PM, Bill Maxwell wrote:

Quote:

As I recall, the characteristic impedance of a folded dipole is 200 ohms, so you would probably need a 1:4 balun to feed it from 50 ohm coax?
Bill

On 21/12/2017 5:06 PM, Neal George wrote:

Quote:
Quote:
--> AeroElectric-List message posted by: Neal George <neal.george(at)gmail.com> (neal.george(at)gmail.com)

Maybe consider a folded dipole?
I’ll have to consult the ARRL Antenna Book...

Neal George
Sent from my iPhone

On Dec 20, 2017, at 11:07 AM, user9253 <fransew(at)gmail.com> (fransew(at)gmail.com) wrote:

--> AeroElectric-List message posted by: "user9253" <fransew(at)gmail.com> (fransew(at)gmail.com)

Since there is not enough room for a dipole, ...




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PostPosted: Thu Dec 21, 2017 8:25 am    Post subject: VHF antenna in the tail Reply with quote

At 12:14 AM 12/21/2017, you wrote:

Quote:
As I recall, the characteristic impedance of a folded dipole is 200 ohms, so you would probably need a 1:4 balun to feed it from 50 ohm coax?

Bill

Actually, closer to 300 ohms. WAAaaayyy back when television
Yagis featuring folded driven elements were a close match
to 300-ohm twin-lead.

Antennas and airplanes just don't really play nicely
together . . . the most elegant solution is almost
always a compromise . . . a departure from that which
can be achieved in terrestrial environs.

Fortunately, VHF communications is (1) mostly short
range and (2) line of sight. Hence, a few watts of
transmitter and a wet string for an antenna will
generally put you in contact with the other station.

For the build in question, the goal is to get as
much of a 1/4 wave, vertically oriented radiator
supported on the leading edge of a composite vertical
fin . . . which MUST be glass/epoxy structure to
minimize RF attenuation.

Then, it would be NICE if we could put an 1/4 wave
radius ground plane around the base.

[img]cid:.0[/img]

Hmmmm . . . that would make for a funny looking airplane . . .
even the first level compromise of crafting a ground
plane from multiple radials is out of question.

Okay, compromise #3, a SINGLE 1/4 wave element that
extends back along the feedline toward the radio. Here's
one of dozens of examples in the DIY antenna crowd.

https://goo.gl/HXCBzh

This article is pretty close. The author stubs his
toe in assuming that the velocity factor of the 'bazooka'
section is the same as the velocity factor of the
coax used to fabricate the feedline and antenna.

In fact, velocity factor is a function of dielectric
characteristics between two conductors, in this case
center conductor and the surrounding shield. For
coax, the dielectric is some material designed
to hold the center conductor alignment while minimizing
losses.

It's true that the outer braid of the bazooka
does form a coaxial section over the
outer braid of the feed line . . . but with a
DIFFERENT dielectric which is not low
loss center conductor support but a robust outer
jacket of the coax that has nothing in common
with the RF characteristics of the inner
insulation. Hence the velocity factor of the
feed line has no relationship to the design
of the de-coupling sleeve.

This antenna can be installed in a glass/epoxy
airplane with the radiating element firmly
built into the vertical fin structure. The
feed line can be fitted with a de-coupling
'bazooka' . . . and essentially treated as
any other feed line.

I've got the test equipment necessary to tune
the de-coupling sleeve to accommodate the new
dielectric/conductor combination . . . but it
will probably be after the first of the year
before I'll be able to get to it.




Bob . . .


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PostPosted: Thu Dec 21, 2017 4:24 pm    Post subject: VHF antenna in the tail Reply with quote

Hi all,

Thanks to all who responded.
Indeed the dipole is out of the question and we'll have to go the 1/4 wave route.


Le 21/12/2017 17:24, Robert L. Nuckolls, III a crit:

Quote:

Okay, compromise #3, a SINGLE 1/4 wave element that
extends back along the feedline toward the radio. Here's
one of dozens of examples in the DIY antenna crowd.

https://goo.gl/HXCBzh

Most interesting.
Maybe this as something in common with the Becker 1A005 ?
http://www.beckerusa.com/Products/1a005-2/
Which we find too expensive at ~100 .

[img]cid:part2.B5DF07BE.5DFF4BD7(at)free.fr[/img]
Quote:



I've got the test equipment necessary to tune
the de-coupling sleeve to accommodate the new
dielectric/conductor combination . . . but it
will probably be after the first of the year
before I'll be able to get to it.


I'd be most interested in your findings in order to craft a bazooka for an acceptable VHF antenna in the tail fin.

Thanks again,
--
Best regards,
Gilles
http://contrails.free.fr
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nuckolls.bob(at)aeroelect
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PostPosted: Fri Dec 22, 2017 4:27 pm    Post subject: VHF antenna in the tail Reply with quote

Quote:
Hi all,

Thank you everyone who responded.
The project is a small airplane with the fin about 800 mm high (~950 mm leading edge), so space seems a bit limited for a dipole antenna.
Still looking into any solution.
The idea is to design something mostly DIY for cost reasons, so this seems to rule out off-the-shelf antennas.
Any ideas ?

BTW, what is the influence of the radiating element width/diameter vs selectivity or else ?
Any hard facts on the subject ?

Can you describe the physical configuration of
the vertical fin vis-a-vis the empennage? Is
the vertical fin detachable?

I presume the antenna, once installed, will
forever more be inaccessible for tweeking?



Bob . . .


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