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Com Setting Off ELT

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MikeEasley(at)aol.com
Guest

Posted: Fri Apr 21, 2006 3:58 am Post subject: Com Setting Off ELT

My friend with a Glasair IIFT has an interesting problem.  The ELT  goes off 

when he transmits on his com radio, sometimes.  It's very  intermittent.  We 

talked to the guys at ACK and they recommended moving the  ELT farther from the 

com antenna cable (RG58).  It's seems to be far enough  away from the com 

antenna, about 5 feet.  We took the ELT out of its  mounting bracket and moved it 

closer to the antenna wire, nothing; closer to the  panel, nothing; closer to 

the antenna, nothing.  We got it to go off with  the remote wiring to the 

panel disconnected and the antenna disconnected, once,  just the ELT box in my 

hand.  We must be getting some leakage from the com  that's activating some 

small electronic device in the ELT.  Or could it be  some buildup of static.  The 

light that's on the panel that flashes when  the ELT is activated flickers 

sometimes when the com is transmitting, sometimes.   



Any ideas?

 

Mike Easley

Colorado Springs

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nuckollsr(at)cox.net
Guest

Posted: Fri Apr 21, 2006 4:42 am Post subject: Com Setting Off ELT

At 07:53 AM 4/21/2006 -0400, you wrote:



 	  Quote: 	
		  



My friend with a Glasair IIFT has an interesting problem.  The ELT  goes off

when he transmits on his com radio, sometimes.  It's very  intermittent.  We

talked to the guys at ACK and they recommended moving the  ELT farther 

from the

com antenna cable (RG58).  It's seems to be far enough  away from the com

antenna, about 5 feet.  We took the ELT out of its  mounting bracket and 

moved it

closer to the antenna wire, nothing; closer to the  panel, nothing; closer to

the antenna, nothing.  We got it to go off with  the remote wiring to the

panel disconnected and the antenna disconnected, once,  just the ELT box 

in my

hand.  We must be getting some leakage from the com  that's activating some

small electronic device in the ELT.  Or could it be  some buildup of 

static.  The

light that's on the panel that flashes when  the ELT is activated flickers

sometimes when the com is transmitting, sometimes.



Any ideas?


	


   Yeah . . . but you're not going to like them.



   We've discussed DO-160 testing criteria that most manufacturers

   subscribe to when building products for aircraft. When ACK

   brought their product onto the market, it's almost a sure bet

   that all powers-that-be recommended and subscribed to some

   level of radiated susceptibility that would be appropriate to

   installation in an all metal airplane where antennas are

   (obviously) on the outside.



   They no doubt conducted the tests and found the product

   acceptable for that environment.



   Now comes the OBAM aircraft owner with an RF transparent

   structure where it's almost a sure bet that the ship's

   VHF comm transmitter is radiating the ELT with more

   RF than the ELT was tested to.



   Just for grins, leave the ELT hooked up to it's antenna.

   Disconnect the control lead. Wrap the ELT in aluminum foil

   such that the foil comes up over the top and wraps as tightly

   around the antenna connector shell as you can make it. I'd

   cut a fat rubber band and use the rubber strip to put lots

   of tensioned turns around the connector shell to press the

   foil against it.



   Now you have an RF tight enclosure with only the antenna

   coming to the outside. It's a reasonably safe bet that

   you'll not be able to duplicate the trips.



   Did somebody stub their toe here? No. The product was

   probably subject to a good faith examination of performance

   for the target market which at the time, did not include

   plastic airplanes. Could they fix it? You betcha. The problem

   is that any changes to design would force a complete

   re-qualification effort in most FAA jurisdictions.  This

   is a prime example of how FAA ignorance of engineering

   and science drives the cost of products up and stifles

   incremental evolutionary improvements. Hence, the cost

   of our computers continue to go down while performance

   improves. Costs of airplane parts goes up while the

   engineers can only dream of what it would be like to

   really have command and control of their destinies.



   Bob . .

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brian

Joined: 02 Jan 2006
Posts: 643
Location: Sacramento, California, USA

Posted: Fri Apr 21, 2006 6:02 am Post subject: Com Setting Off ELT

MikeEasley(at)aol.com wrote:

 	  Quote: 	
		   

 

 My friend with a Glasair IIFT has an interesting problem.  The ELT  goes off 

 when he transmits on his com radio, sometimes.  It's very  intermittent.  

 ...

 

 Any ideas?


	


It is likely to be RF getting into the remote control interface that is 

the problem although I am surprised that it goes off with the remote 

disconnected. I would wind the remote control cable through toroid cores 

at both ends (remote and ELT) to see if that helps.



But given that this is not a common complaint I would also consider that 

it might be a problem with the ELT itself.



-- 

Brian Lloyd                         361 Catterline Way

brian-yak at lloyd dot com          Folsom, CA 95630

+1.916.367.2131 (voice)             +1.270.912.0788 (fax)



I fly because it releases my mind from the tyranny of petty things . . .

- Antoine de Saint-Exupery

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_________________
Brian Lloyd
brian-yak at lloyd dot com
+1.916.367.2131 (voice) +1.270.912.0788 (fax)

I fly because it releases my mind from the tyranny of petty things . . .
- Antoine de Saint-Exupery

aadamson(at)highrf.com
Guest

Posted: Fri Apr 21, 2006 6:25 am Post subject: Com Setting Off ELT

I have discovered this exact same problem on a Mooney M20C that I fly.

Doesn't happen all the time, but will occasionally.  What we found was that

the coax connector for the Comm antenna at the antenna, which happens to be

back in the same area of the ELT, was bad.  It might be the coax itself as

well.  Anyway, stray RF traveling thur the "ground system" will likely cause

this.  We swapped out the coax and connectors and the problem went away.



Alan 



--

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geekdownrange(at)gmail.co
Guest

Posted: Fri Apr 21, 2006 10:50 am Post subject: Com Setting Off ELT

Mike,



Have you tried a choke balun at the antenna end of the comm radio

coax?  If you have available cable slack you could try 6-10 turns

around something roughly the diameter of a clenched fist (remove the

form after winding).  Alternatively, you could cut the antenna end

connector off the coax, install about 50 ferrite beads over the end of

the cable (FB73-2401 might a a good choice), and then sleeve the beads

with heat shrink.



Since coax is an unbalanced transmission line, connecting to a

balanced antenna can readily put common mode RF currents on the

feedline.  As an experiment, you could gather up a number of the

ferrite split-beads like are often delivered with computer monitors or

other electronic devices.  While not a good permanent solution, it may

lower the level of common-mode signals enough to help indicate if you

are on the right track.



--Brian

On 4/21/06, MikeEasley(at)aol.com <MikeEasley(at)aol.com> wrote:

 	  Quote: 	
		   



 My friend with a Glasair IIFT has an interesting problem.  The ELT  goes off

 when he transmits on his com radio, sometimes.  It's very  intermittent.  We

 talked to the guys at ACK and they recommended moving the  ELT farther from the

 com antenna cable (RG58).  It's seems to be far enough  away from the com

 antenna, about 5 feet.  We took the ELT out of its  mounting bracket and moved it

 closer to the antenna wire, nothing; closer to the  panel, nothing; closer to

 the antenna, nothing.  We got it to go off with  the remote wiring to the

 panel disconnected and the antenna disconnected, once,  just the ELT box in my

 hand.  We must be getting some leakage from the com  that's activating some

 small electronic device in the ELT.  Or could it be  some buildup of static.  The

 light that's on the panel that flashes when  the ELT is activated flickers

 sometimes when the com is transmitting, sometimes.



 Any ideas?



 Mike Easley

 Colorado Springs

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