gmcjetpilot
Joined: 04 Nov 2006
Posts: 170
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 Posted: Sat Mar 08, 2008 8:02 am Post subject: Cheap "Coat Hanger" antenna (was Coax termination elect theo |
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No offense to Ernest or Bob, the old coat hanger
antennas that you terminated the coax with crimp on
lugs has not been used in production airplanes since
the 50's or early 60's.
Coat hanger antenna
http://www.aircraftspruce.com/catalog/avpages/av534.php
What Eric says about "EM field energy", which I recall
bits from physics and armature radio, the coax,
BNC connector is way more efficient. That inch of
exposed shield/core & important lost insulation does
count. The "coat hanger antenna connections are
subject to corrosion and fatigue way more than a BNC
connector. Just my opinion.
No one is seriously using the coat hanger wire antenna
on new OEM aircraft any more.
"Testimonials" that they work in the plane or bench are
great, but unless you do a test on the airframe in an
antenna test chamber (EMF / RF anechoic chamber),
we are guessing. Besides performance there is the
reliability of the installation.
Just from an installation standpoint, spend the $124
for the real antenna and leave the $50 coat hanger
antenna for the closet. Antenna energy, non-ionizing
radiation is EMF energy at high frequencies. It needs
"ducting" to be most effective.
Does the "strip-it crimp-it" antenna connection work?
Yes it "works", but gosh ughaaa, ugly.
We're talking about 5-8 watts of energy and communications
of 5 to 50 mile, line of sight, listening for even more powerful
transmitters, usually without obstacles. We can get away
with a weak antenna.
The coat hanger works, but its not ideal. We have better
ways. If I was restoring a classic Beech or something, yea
I'd keep the coat hanger antenna. Other wise coat hangers
are for the closet (pun intended).
$110-$150 for newer antenna design
http://www.aircraftspruce.com/catalog/avpages/av17.php
PS: Some have experienced RFI with unshielded antenna
connections thru gauges and avionics.
>From: Ernest Christley <echristley(at)nc.rr.com (echristley(at)nc.rr.com)>
| Quote: | Subject: Re: Coax termination and electrical theory
explained.
|
>Eric M. Jones wrote:
>> Bob, in my humble opinion, needs a little nudge
>> on this. Here's how NOT to terminate coaxial
>> cable--
http://aeroelectric.com/articles/shldwire/shldwire.html
>The difference between theory and practice is that in
| Quote: | theory they are the same.
|
> You have two copper strips to form an
| Quote: | antennae. One must be connected to the center
conductor, the other to the shield. Whether you
terminate the coax with some fancy, expensive
solution from an electronics catalogue or Bob's
method, at some point the center conductor has to
split out from the shield. The difference in actual
performance in the flying airplane will be lost in
the noise (pun intended). In theory, there is an
advantage in the expensive, complicated solution.
In practice, the advantage ain't worth the
headache.
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