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ELT antenna requirements

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bbradburry(at)bellsouth.n
Guest

Posted: Wed Mar 19, 2008 4:41 pm Post subject: ELT antenna requirements

I will be installing the Artex ME406 w/110-773 whip antenna.  It broadcasts

on 121.5 and 406 Mhz.

I am installing it in an E-glass plane.  What is the mimimum ground plane

that will work.  The instructions are suggesting that the ground plane

radius should be 24" in all directions! The plane is not 4' wide at any

point in the fuselage!!?

I really don't have much room for this install since I am trying to keep all

the antennas inside the plane.

Does anyone have a suggestion as to how I can install this antenna or make a

half wave that doesn't require a ground plane?



Bill B

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mprather(at)spro.net
Guest

Posted: Wed Mar 19, 2008 5:38 pm Post subject: ELT antenna requirements

The ground plane can curve - to some extent following the contour of the

fuse.  I imagine that if the radiator is in the middle of the fuse and the

ground plane wraps very far up the sides, performance will suffer to some

extent, though performance may still be acceptable to you.



What type of antenna have other builders used?  External?



Is it possible to install the antenna in the fin?  Is it e-glass also? 

You may be able to install an antenna that looks electrically like a 1/4

wave dipole, but is more physically compact in length (height).  How tall

is the fin?

Regards,



Matt-

 	  Quote: 	
		   

 <bbradburry(at)bellsouth.net>



  I will be installing the Artex ME406 w/110-773 whip antenna.  It

 broadcasts

 on 121.5 and 406 Mhz.

 I am installing it in an E-glass plane.  What is the mimimum ground plane

 that will work.  The instructions are suggesting that the ground plane

 radius should be 24" in all directions! The plane is not 4' wide at any

 point in the fuselage!!?

 I really don't have much room for this install since I am trying to keep

 all

 the antennas inside the plane.

 Does anyone have a suggestion as to how I can install this antenna or make

 a

 half wave that doesn't require a ground plane?



 Bill B

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nuckolls.bob(at)cox.net
Guest

Posted: Wed Mar 19, 2008 6:52 pm Post subject: ELT antenna requirements

At 08:36 PM 3/19/2008 -0400, you wrote:



 	  Quote: 	
		  

<bbradburry(at)bellsouth.net>



  I will be installing the Artex ME406 w/110-773 whip antenna.  It broadcasts

on 121.5 and 406 Mhz.

I am installing it in an E-glass plane.  What is the mimimum ground plane

that will work.  The instructions are suggesting that the ground plane

radius should be 24" in all directions! The plane is not 4' wide at any

point in the fuselage!!?

I really don't have much room for this install since I am trying to keep all

the antennas inside the plane.

Does anyone have a suggestion as to how I can install this antenna or make a

half wave that doesn't require a ground plane?


	




The ground plane radials need to be 24" long but not necessarily

flat. The easiest way to make this happen is to mount a "patch"

of brass sheet (shim stock, sheet stock from hobby shop) about

3" diameter on the inside surface of the skin centered on your

antenna location. Copper foil is nice stuff to make radials out

of but copper wire will work too. Further, it's easier to find

(a 6 foot piece of 12x2 Romex with ground will yield 18' total

of 12AWG solid wire). Solder as many 23" pieces of 12AWG

wire as you are willing to mess with to the edge of your

brass grounding pad at the base of the antenna. Route radials

away from antenna following inside contours of skin. Stick each

radial to the skin with patches of BID glass and 5 minute epoxy.

4 radials is about the minimum, return on investment of time

beyond 8 radials is poor.



Recommend you stay with the supplied antenna . . . it may have

features that enhance its two-frequency performance.



Bob . . .

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paula.alvary(at)verizon.n
Guest

Posted: Thu Mar 20, 2008 5:38 am Post subject: ELT antenna requirements

I have an Ameriking AK450 ELT (121.5/243.0MHz) also in a plastic plane. The

ELT antenna was broken when I got the plane so I calculated the optimal

length and made a whip antenna out of welding rod. I simply soldered the rod

to the center BNC conductor and insulated the section coming out of the BNC

shell area. To fit the approx. 23" antenna in the space I had to bend it 90

degrees over a 2" radius, about 5" from the BNC. My biggest concern was lack

of ground plane, but I was hoping the ELT itself acted as a ground plane.

Even I know this is not optimal, but is it "workable"?



--Jose

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nuckolls.bob(at)cox.net
Guest

Posted: Thu Mar 20, 2008 8:54 am Post subject: ELT antenna requirements

At 09:27 AM 3/20/2008 -0500, you wrote:



 	  Quote: 	
		  



I have an Ameriking AK450 ELT (121.5/243.0MHz) also in a plastic plane. The

ELT antenna was broken when I got the plane so I calculated the optimal

length and made a whip antenna out of welding rod. I simply soldered the rod

to the center BNC conductor and insulated the section coming out of the BNC

shell area. To fit the approx. 23" antenna in the space I had to bend it 90

degrees over a 2" radius, about 5" from the BNC. My biggest concern was lack

of ground plane, but I was hoping the ELT itself acted as a ground plane.

Even I know this is not optimal, but is it "workable"?


	


  Depends on what how we define "workable". The task of getting some

  manifestation of energy stored on the ELT's batteries to an overhead

  satellite is burdened with many losses and pitfalls in the conversion

  and conduction of energy. The batteries will deliver at 10-14 volts,

  the satellite will hear your ELT if the signal arrives at the

  1 to 10 MICROvolt level.



  The weakest link in the energy conduction process is the antenna.

  It has no way of knowing where the satellite is so it spreads

  your signal all over the sky . . . and ground too. Everything

  you do that departs from the best-we-know-how-to-do adds another

  degree of uncertainty to the probability that the satellite gets

  a useful signal.



  On the other side of the coin, the probability that this piece

  of equipment will be a major contributor to your surviving the

  unplanned arrival with the earth is low. An article published

  in one of the journals a couple of years ago cited something

  much less than 10% of recovery situations where the ELT figured

  strongly in the success of the operation.



  The departures you've described from "ideal" will no doubt

  degrade the benchmark performance of the system. Will it

  make the difference between your pile of bent aluminum being

  found or not found? Probably not. Your failure to make good

  on a flight plan followed by a decision by someone to go

  looking for you is more likely to initiate any sort of

  rescue action. Then, if search aircraft also happen to carry

  receivers and direction finding equipment for ELT frequencies,

  then even your degraded performance MIGHT be of some assistance

  in finding you sooner . . . if ever.



  If you're putting much faith in the utility of this device

  to make the difference between surviving or not, then one

  of the more sophisticated devices is called for. One that

  transmits your last known GPS position. You can also consider

  an internal antenna like this:



http://www.aircraftspruce.com/catalog/avpages/antennasystems.php



  At the very least, put a ground plane under the antenna you described

  above. I posted a recommended process on adding ground planes

  to plastic antennas to the List yesterday.



  Alternatively, making your ELT a hand-held device with

  a full length, telescoping antenna gets around a lot of

  installation hassles.



  Bob . . .

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