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ELT antenna inside tube and fabric fuselage

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nuckolls.bob(at)aeroelect
Guest

Posted: Thu Mar 07, 2013 5:57 am Post subject: ELT antenna inside tube and fabric fuselage

At 07:34 AM 3/7/2013, you wrote:

  	  Quote: 	
		  They are, but according to posters on the J-sCub.com site Comm radio reception and transmit is very good with a dipole antenna from Advance Aircraft Electronics mounted inside.Â  No one has addressed the ELT antenna but as I mentioned the ACK folks say installation inside of a (steel) tube and fabric fuselage will meet their criteria if the fabric is non-conductive. 	


    Interesting. I'm surprised that they would

    climb out on that 'limb' unless their tests

    for achieving TSO status included that

    configuration . . . which I doubt.



    Discussions like this are fraught with

    the effects of variables that are unknown

    and therefore cannot be part of the 

    deliberations. I do know that the uhf

    signal is less likely to be severely

    trashed by a surrounding, open mesh

    'cage'.  It would be interesting to

    conduct some A-B experiments comparing

    an internal antenna with an external

    antenna with the assistance of some hams

    having 70 cm radios and some rudimentary

    tools for comparing signal strengths.



    But suppose you deduced that for most

    situations, the internal antenna was about

    10 db down from the external one. Now what?

    By what criteria is acceptability to be

    judged? Without knowing the system's margins

    for performance under various signal levels,

    having such numbers doesn't go much beyond

    'interesting'.



    Be wary of advice that does not come from

    someone who has access to applicable data

    and knows how to interpret it. This applies

    especially to individuals in the employ of

    regulatory agencies who can exert power over

    your activities.



    The reports from fellow pilots about the

    performance of internally mounted VHF antennas

    is interesting. It's great if the installation

    meets their communications needs. But their

    observations are not quantified data. The

    up side is that the physics is on your side.

    The UHF feature on the modern ELT will be BETTER

    disposed to adequate performance than the

    VHF comm antenna.



    The off-hand advice from folks without

    numbers may NOT be on your side.



 

   Bob . . .    [quote][b]

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klehman(at)albedo.net
Guest

Posted: Thu Mar 07, 2013 7:50 am Post subject: ELT antenna inside tube and fabric fuselage

An external antenna might reduce occupant exposure to additional RF 

transmission energy if that is a concern to someone. Might also reduce 

the rare RF caused instrumentation glitches that have been reported here.

Just a wild guess.

Ken



On 07/03/2013 8:56 AM, Robert L. Nuckolls, III wrote:

 	  Quote: 	
		   At 07:34 AM 3/7/2013, you wrote:

> They are, but according to posters on the J-sCub.com site Comm radio

> reception and transmit is very good with a dipole antenna from Advance

> Aircraft Electronics mounted inside.Â  No one has addressed the ELT

> antenna but as I mentioned the ACK folks say installation inside of a

> (steel) tube and fabric fuselage will meet their criteria if the

> fabric is non-conductive. **



     Interesting. I'm surprised that they would

     climb out on that 'limb' unless their tests

     for achieving TSO status included that

     configuration . . . which I doubt.



     Discussions like this are fraught with

     the effects of variables that are unknown

     and therefore cannot be part of the

     deliberations. I do know that the uhf

     signal is less likely to be severely

     trashed by a surrounding, open mesh

     'cage'.  It would be interesting to

     conduct some A-B experiments comparing

     an internal antenna with an external

     antenna with the assistance of some hams

     having 70 cm radios and some rudimentary

     tools for comparing signal strengths.



     But suppose you deduced that for most

     situations, the internal antenna was about

     10 db down from the external one. Now what?

     By what criteria is acceptability to be

     judged? Without knowing the system's margins

     for performance under various signal levels,

     having such numbers doesn't go much beyond

     'interesting'.



     Be wary of advice that does not come from

     someone who has access to applicable data

     and knows how to interpret it. This applies

     especially to individuals in the employ of

     regulatory agencies who can exert power over

     your activities.



     The reports from fellow pilots about the

     performance of internally mounted VHF antennas

     is interesting. It's great if the installation

     meets their communications needs. But their

     observations are not quantified data. The

     up side is that the physics is on your side.

     The UHF feature on the modern ELT will be BETTER

     disposed to adequate performance than the

     VHF comm antenna.



     The off-hand advice from folks without

     numbers may NOT be on your side.



    Bob . . .

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nuckolls.bob(at)aeroelect
Guest

Posted: Thu Mar 07, 2013 8:21 am Post subject: ELT antenna inside tube and fabric fuselage

At 09:20 AM 3/7/2013, you wrote:

 	  Quote: 	
		  I'd mount all the antenna's outside. If there's enough aluminum in 

the dope to protect the fabric from UV, it's going to be pretty 

reflective of the RF from the radios. To much reflected power back 

into the antenna can damage transmitters. Having your ELT inside, at 

the very least, is going to reduce the range and make you harder to find.


	


    The effects of suspended metal in aircraft

    fabric finishes has been a point of debate

    for years. It would be interesting to do some

    experiments to explore real effects.



    If anyone has the materials on hand to "finish"

    an experimental enclosure (about the size of a

    shoe box) as if it were a rag cover, I'd be

    willing to use said enclosure to make some

    shade tree measurements on radiation effects.



    Further, having such a test article on hand

    would offer an opportunity to do some lab

    measurements at some time in the future wherein

    I have access to the facilities.



    If somebody can help produce the test enclosure,

    drop me a note and let's discuss materials

    and techniques.  Thanks!



   Bob . . .

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email(at)jaredyates.com
Guest

Posted: Thu Mar 07, 2013 9:36 am Post subject: ELT antenna inside tube and fabric fuselage

I have polyfiber leftovers to cover a box like that, and could use the opportunity as a covering demo/training for someone else. 



On Mar 7, 2013, at 11:20, "Robert L. Nuckolls, III" <nuckolls.bob(at)aeroelectric.com> wrote:



 	  Quote: 	
		   

 

 At 09:20 AM 3/7/2013, you wrote:

> I'd mount all the antenna's outside. If there's enough aluminum in the dope to protect the fabric from UV, it's going to be pretty reflective of the RF from the radios. To much reflected power back into the antenna can damage transmitters. Having your ELT inside, at the very least, is going to reduce the range and make you harder to find.

 

   The effects of suspended metal in aircraft

   fabric finishes has been a point of debate

   for years. It would be interesting to do some

   experiments to explore real effects.

 

   If anyone has the materials on hand to "finish"

   an experimental enclosure (about the size of a

   shoe box) as if it were a rag cover, I'd be

   willing to use said enclosure to make some

   shade tree measurements on radiation effects.

 

   Further, having such a test article on hand

   would offer an opportunity to do some lab

   measurements at some time in the future wherein

   I have access to the facilities.

 

   If somebody can help produce the test enclosure,

   drop me a note and let's discuss materials

   and techniques.  Thanks!

 

 

 

  Bob . . .

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Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:

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