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Antennas



 
 
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  #1  
Old April 21st 05, 03:20 PM
Terry
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Default Antennas

Thanks, John. The reason that I'm looking for something other than a
standard 1/4 wave antenna is that I have one of those now, and it
isn't working. I know nothing about antennas other than what I've
read on the 'net, but I've been told that the location of mine isn't
the best. It's on the wing root fairing, and from what I've been
told, this doesn't give it the most optimized ground plane. I read of
a case where a guy with a PA-11 had the same problem, and installed a
folded dipole inside the fuselage and it worked great. I thought
maybe the folded dipole or a copper tape system might help me out
without moving the antenna around and drilling all kinds of holes in
the sheet metal. All I need is something for communications with my
handheld in order to talk to the occasional tower--nothing heavy duty
at all. I'm open to any suggestions.

Thanks again,

Terry
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  #2  
Old April 22nd 05, 01:38 AM
COLIN LAMB
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There are two separate issues - at least. A dipole antenna is simply a 1/2
wave antenna fed in the middle, so that a 1/2 wave is on each side. In
effect, each half element reacts with the other half. A 1/4 wave ground
plane simply replaces one of the elements with a plane perpendicular to the
other.

The second issue is polarity. It just happens that many dipoles happen to
be mounted horizontally, while verticals are mounted vertically. A dipole
can also be mounted vertically. Polarity should be the same or there will
likely be a severe signal decrease between stations. By convention,
aircraft vhf communications is vertically polarized.

It is difficult to analyze your problem with the sketchy information given,
but basically an antenna is an antenna. If your 1/4 ground plane does not
work at all, a dipole will not work, either. Replace of one with another
will simply postpone finding the real problem.

The most likely problem is the antenna connectors. Unless they are
assembled correctly, the entire system will fail.

Even though the location of your antenna may not be the best, it should be
adequate for what you want. Your champ is a fabric airplane, so you will
need a "ground plane for the 1/4 wave vertical. This can be as simple as a
24" wire attached to the base and extending out. In fact, that will turn it
into a dipole. But even that will not cure a bad connection. It is also
possible the radio has a problem, but I would not expect that.

Find someone who can assist you to check things out. It is very difficult
to diagnose the real problem without being there.

Colin N12HS


  #3  
Old April 22nd 05, 01:43 AM
COLIN LAMB
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Correction: Each half of a 1/2 wave antenna is a 1/4 wave. I was suffering
from moderate hunger when I typed the response.

Colin


  #4  
Old April 22nd 05, 03:14 AM
UltraJohn
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Terry wrote:

Thanks, John. The reason that I'm looking for something other than a
standard 1/4 wave antenna is that I have one of those now, and it
isn't working. I know nothing about antennas other than what I've
read on the 'net, but I've been told that the location of mine isn't
the best. It's on the wing root fairing, and from what I've been
told, this doesn't give it the most optimized ground plane. I read of
a case where a guy with a PA-11 had the same problem, and

installoptimumfolded dipole inside the fuselage and it worked great. I
thought
maybe the folded dipole or a copper tape system might help me out
without moving the antenna around and drilling all kinds of holes in
the sheet metal. All I need is something for communications with my
handheld in order to talk to the occasional tower--nothing heavy duty
at all. I'm open to any suggestions.

Thanks again,

Terry

Read Colins reply,
also you might try just taping a 1/2 wave dipole to the inside of your
windshield near the bottom so it's not interrupting your view. Put the
middle of the dipole in the mid point of the windshield and feed the coax
straight back use a double sided sticky cable tie block on the edge of the
dash to cable tie the coax to for a strain relief and see if that works. If
your windshield isn't wide enough to fit the dipole just bend the ends up
alongside the edges of the windshield. Yes I know that's not optimum but
hams have been doing it for eons and it will work. If you want you can
mount the center on either side of the windshield with the middle centered
top to bottom to get vertical polarity.
John

 




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