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ELT Antenna (406MHz) - Copper Dipole style...will this work?

 
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plevyakh



Joined: 10 Jan 2011
Posts: 39

PostPosted: Fri Dec 07, 2012 4:43 pm    Post subject: ELT Antenna (406MHz) - Copper Dipole style...will this work? Reply with quote

Folks,
I'm building a GlaStar (composite glass fuselage with metal wings and control surfaces).

I'm going with INTERNAL mount for the antenna, and will be placing it just AFT of my bulkhead "A" as one of the most survivable locations in a crash for my aircraft.

I have the ACK E-04 unit and it comes with it's own antenna, but that requires creating a 48" dia. ground plane! (24" long copper foil elements, per the E-04 Install guide). I don't have the room for this in the tail cone...given I have other stuff back there in the way.

I have one of Jim Weir's RS-802 Copper Dipole Antenna kits and I was going to make my own. His kit dwg 802-8905 shows how to create one for the older style 121.5 units. So I'm thinking I'd use this same X cross style antenna, and have one V with Lengths = 22.5" (121.5MHz), and the other V with lengths = 7.3" (406MHz).

This should fit nicely onto the sidewall of the tunnel AFT of Bulkhead "A" in a vertically mounted position (see attached dwg).

Am I correct in my modification of the Jim Weir design to be able to accommodate the 406MHz frequency?

Are there any other changes I need to make with this double V design to make it work?

Has anyone run into a problem in their Final FAA inspection in getting approval to use a "Double V style antenna"?

Thanks for any thoughts.
Howard


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ELT Copper Foil Dipole X Design.jpg
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ELT "Double V" copper dipole antenna
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ELT Copper Foil Dipole X Design.jpg



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Howard Plevyak
GlaStar / Cincinnati, Ohio
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tim2542(at)sbcglobal.net
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PostPosted: Fri Dec 07, 2012 6:10 pm    Post subject: ELT Antenna (406MHz) - Copper Dipole style...will this work? Reply with quote

Hi Howard, I ran into this same problem on my Cozy and studied doing a home brew antenna myself. Eventually I was able to make a ground plane for the provided antenna by running 4 wires out from the TSO'd antenna, not the 6 they call for but the best I could do. So if you do build your own dual band dipole my suggestion is build it first on cardboard or similar, then go buy a box of doughnuts and stop in the local 2 way communications dealer and see if they will put their analyzer on it and check its resonance on both bands. Most city or county fire dept or law enforcement agency will have some of these guys floating around also.
As for the legal side it won't be without the TSO antenna. Period.
On the practical side you don't have to have a ELT in phase 1 anyway. Leave it out until you have what you need from the DAR and then the rest is on you.
Myself, I wouldn't lose any sleep over doing it this way, but you may carry PX sometime and you need to consider them also. But the other side of that equation, if you want to rationalize a bit, is the 406/121.5 gps-fed system you have with a home brew antenna will be far better than the second hand $25 ELT that is still legal to install.
Tim

Sent from my iPad

On Dec 7, 2012, at 4:43 PM, "plevyakh" <hplevyak(at)mac.com> wrote:

Quote:


Folks,
I'm building a GlaStar (composite glass fuselage with metal wings and control surfaces).

I'm going with INTERNAL mount for the antenna, and will be placing it just AFT of my bulkhead "A" as one of the most survivable locations in a crash for my aircraft.

I have the ACK E-04 unit and it comes with it's own antenna, but that requires creating a 48" dia. ground plane! (24" long copper foil elements, per the E-04 Install guide). I don't have the room for this in the tail cone...given I have other stuff back there in the way.

I have one of Jim Weir's RS-802 Copper Dipole Antenna kits and I was going to make my own. His kit dwg 802-8905 shows how to create one for the older style 121.5 units. So I'm thinking I'd use this same X cross style antenna, and have one V with Lengths = 22.5" (121.5MHz), and the other V with lengths = 7.3" (406MHz).

This should fit nicely onto the sidewall of the tunnel AFT of Bulkhead "A" in a vertically mounted position (see attached dwg).

Am I correct in my modification of the Jim Weir design to be able to accommodate the 406MHz frequency?

Are there any other changes I need to make with this double V design to make it work?

Has anyone run into a problem in their Final FAA inspection in getting approval to use a "Double V style antenna"?

Thanks for any thoughts.
Howard

--------
Howard Plevyak
GlaStar / North Bend, Ohio
hplevyak(at)mac.com




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