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fireflier
Joined: 24 Jun 2012 Posts: 58
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Posted: Mon Dec 03, 2012 1:42 am Post subject: Antenna installations |
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Hello everyone
I'm now at the stage of thinking about the installation of antenna's for my comm & transponder. The reason for my post is to seek the opinion of fellow forum members on the best location to install the antenna's and also to ask what antenna's people have used?
I have been looking at the following nav/comm antenna
http://shop.airworlduk.com/high-gain-nav--com-antenna-5t-302140-1080-p.asp
Has anyone got any experience of this antenna? I would be interested to hear your thoughts and reviews of it.
I look forward to receiving your thoughts & comments with regards to correct antenna selection, placement within aircraft etc.
Many thanks for your time reading my post.
Kind regards
Donald.
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houlihan(at)blueyonder.co Guest
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Posted: Mon Dec 03, 2012 2:22 am Post subject: Antenna installations |
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Re aerials for Comms etc.What is wrong with the aerial described in the build manual ?
The link you sent shows a di pole aerial and claims its Hi gain ! ! how hi-gain ? It is not stated but is probably a 1/2 wave dipole exactly like the one described in the manual.
It also states that it can be used within the wingtip of a metal aircraft " They will work in metal airframes when a plastic or fiberglass wing tip or similar plastic component is available to provide the mounting structure" that implies that the aerial is mounted horizontally ( unless the wing is several feet thick ) and so will not match the comms VHF system which is vertically polarised.
I recently had a problem with my standard fin closeout mounted aerial but that was caused by a poor intermittent contact in the BNC connecter . When it was connected correctly it seemed to be delivering perfectly adequate performance at a much lower price.
I am sure that experts will have their views on this but my reading of the article raises real technical questions regarding the claims made in it.
Tim H
G-BZTH
p.s. a length of RG58 coax with the last 1/2 meter or so stripped out and the inner core and outer screen separated and mounted vertically one up and one down will act as a very usable aerial
On 3 December 2012 09:42, fireflier <fireflier(at)btinternet.com (fireflier(at)btinternet.com)> wrote:
[quote]--> Europa-List message posted by: "fireflier" <fireflier(at)btinternet.com (fireflier(at)btinternet.com)>
Hello everyone
I'm now at the stage of thinking about the installation of antenna's for my comm & transponder. The reason for my post is to seek the opinion of fellow forum members on the best location to install the antenna's and also to ask what antenna's people have used?
I have been looking at the following nav/comm antenna
http://shop.airworlduk.com/high-gain-nav--com-antenna-5t-302140-1080-p.asp
Has anyone got any experience of this antenna? I would be interested to hear your thoughts and reviews of it.
I look forward to receiving your thoughts & comments with regards to correct antenna selection, placement within aircraft etc.
Many thanks for your time reading my post.
Kind regards
Donald.
--------
Fireflier
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=389723#389723
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frans(at)privatepilots.nl Guest
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Posted: Mon Dec 03, 2012 7:28 am Post subject: Antenna installations |
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On 12/03/2012 10:42 AM, fireflier wrote:
Humbug.
Go for the antenna as proposed in the build manual. That is a half wave
dipole, correctly polarized, and there is just nothing that can beat a
vertical half wave antenna in an aircraft. No antenna can give you more
gain, except when compromising the radiation pattern thus sacrificing
some coverage, which might be fine for a stationary antenna, but not for
an aircraft.
As for connecting multiple devices to one antenna: don't do it. You will
create ground loops, difficult to troubleshoot interference, etc.
Frans
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skanderup
Joined: 10 Jan 2010 Posts: 11 Location: Denmark
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Posted: Mon Dec 03, 2012 8:32 am Post subject: Re: Antenna installations |
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Hi,
Now the talk is on antennas, I would like to ask the forum for your guidance on ground plane.
I have purchased a nice antenna for my transponder and it requires a ground plane (which a GP aircraft does not provide automatically like a metal plane...)
Any good advise on how to make one, materials, sizes etc?
Any advise and photos is much appreciated.
Regards,
Allan Skanderup Nielsen
Kit 0622, OY-EEK
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frans(at)privatepilots.nl Guest
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Posted: Mon Dec 03, 2012 8:53 am Post subject: Antenna installations |
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On 12/03/2012 05:32 PM, skanderup wrote:
Quote: |
Hi,
Now the talk is on antennas, I would like to ask the forum for your guidance on ground plane.
I have purchased a nice antenna for my transponder and it requires a ground plane (which a GP aircraft does not provide automatically like a metal plane...)
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I hope you bought the TED antenna as it is the best available and also
very affordable.
A ground plane should be at least a quarter wave in radius. Quarter wave
is the lenght of the antenna rod. A larger ground plane is ok, but has
not much additional benefit.
In my tri-gear I cut out the monowheel opening and use an aluminium
plate to cover it. I mounted the antenna on the underside of the metal
plate, and it works very well.
As these radio waves are going through the glass fuselage, you could
mount the antenna somewhere inside as well, and use any metal plate
available. It is advisable to mount the antenna "upside down", that is,
the metal rod sticking down. Beware of "shadows" like from the engine,
so keep it as low as possible.
Frans
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frans(at)privatepilots.nl Guest
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Posted: Mon Dec 03, 2012 10:10 am Post subject: Antenna installations |
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On 12/03/2012 06:42 PM, houlihan wrote:
Quote: | I agree entirely with Frans reply,
I was told during a conversation with the Trigg development engineers
some time ago not to use a perfectly circular ground plane at the
calculated diameter as it could possibly resonate and interfere with the
signal in some way , the reasoning as to why was well above my pay grade .
It is very easy to avoid this phenomena by making the ground plane
slightly irregular.
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Reason of this is that if it is exactly circular, it resonates at
exactly one frequency, i.e. it is very narrow banded. The transmitting
and receiving of the transponders is on different frequencies, so you
need to avoid extremely narrow banded antenna's. Keep in mind that
resonance not only happens at one quarter wavelength, but also at
multiplies and certain fractions of the wavelength. If you use a true
circular ground plane chances are you are hitting a resonant somewhere.
If it is not exactly 1/4th maybe it happens to be 5/16th?
If you make the ground plane a little bit irregular, each frequency is
able to find a matching resonant size somewhere on this shape, so the
sum of the total lengths possible results in a much wider band width.
Electromagnetic resonance is quite similar to accoustic resonance, I
guess if you try to build a quitar with a circular body it would be
difficult to tune and some notes would play much louder than others,
hence the irregular shape of guitars, which function to make its
frequency response (resonance) much wider than that of a circular shape.
So, put the antenna not exactly in the middle if you use a circular
ground plane, or better yet, use a rectangular ground plane, so the
electrons see various distances to the edge of the ground plane.
I guess a guitar shaped ground plane would serve your transponder also
very well.
Frans
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