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Thread: ELT Antenna: vertical or horizontal?

  1. #61
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    Default Re: ELT Antenna: vertical or horizontal?

    😂. I love common sense. A seemingly rare quality these days!

    Quote Originally Posted by ceslaw View Post
    The January issue of Kitplanes has an article written by Jim Weir which discusses a simple ELT antenna that will work on both 121.5 MHz and 406 MHz. In order to make a simple dipole work on both bands it detunes the function on 121.5 MHz resulting in an SWR approaching 3:1. It is an option, although not one I would prefer.
    What is interesting is the comment regarding the position for mounting the antenna: The question has often been asked of me, ‘Should the ELT antenna be mounted horizontally or vertically?’ The answer has always been the same: If you can tell me the orientation of the crumpled remains of the fuselage in the middle of the dust cloud when you really need the ELT, I can tell you the orientation. In my experience, a random guess is every bit as good as anything else. This is the same point noted previously in this thread.
    Dave Embry
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  2. #62
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    Default Re: ELT Antenna: vertical or horizontal?

    Today for the 7th build…..once again the Elt/antenna/CubCrafters bracket system does not work. There is a flaw with the bracket ground plane system (or I have the worst luck in the world.)

    Once again I installed their bracket to the rear of the baggage panel. Installed the coax and check continuity before and after connecting it to the antenna. Then connected the antenna and to the Kannad ELT unit and switched it to the ARM position and as always I got the self test failure with the 3-5 code. Antenna/ground plane.

    I was out of aluminum to build my usual ground plane and saw this leftover heat shield material I used on the heat duct in the floorboard and noticed it had “foil” on the one side. The Installation Manual says to put foil strips as a ground plane on fabric planes!

    So for fun, I cut a hole and installed it between the antenna and the bracket and it works perfectly. I've ordered some 1" wide copper grounding foil and will use that as it's lighter than aluminum ground plane panel and the instructions show using strips "at least as long as the antenna" radiating out from the antenna base. I will try and attach and use it like this heat shield and see if I can still use the mounting bracket but use the foil for the ground. I don't have the testing equipment to test the signal but this gets the unit to self test good.

    The CC system of installing the antenna on the bracket for the Kannad is incorrect. It doesn’t work. I don’t know how people units test ok?

    45A41FAD-1C0E-477A-B203-A569DD241C82.jpg
    Last edited by Daveembry; 12-30-2021 at 08:38 AM.
    Dave Embry
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  3. #63
    Senior Member ceslaw's Avatar
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    Default Re: ELT Antenna: vertical or horizontal?

    I sense your frustration. I agree, it is pretty clear there is a flaw in the design for proper function on 121.5 MHz, leading to flawed self check with the Kannad. The ground plane needs to be at the antenna base.

    You have essentially created a proper ground plane at the antenna base, solving the problem, with the foil.

    Would the single radial noted in a previous post be a more elegant solution vs a large piece of foil?

  4. #64
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    Default Re: ELT Antenna: vertical or horizontal?

    Quote Originally Posted by ceslaw View Post
    I sense your frustration. I agree, it is pretty clear there is a flaw in the design for proper function on 121.5 MHz, leading to flawed self check with the Kannad. The ground plane needs to be at the antenna base.

    You have essentially created a proper ground plane at the antenna base, solving the problem, with the foil.

    Would the single radial noted in a previous post be a more elegant solution vs a large piece of foil?
    well like I said, I’ve ordered the copper foil in 1” and intend to install it with numerous strips all in all directions per their installation manual. This big piece of the temp shield was just a test (almost a joke!). Almost ANYTHING seems to work as long as you add a ground plane. Their bracket doesn’t work.

    Once I get the foil in and install and test I’ll post more pics here and on my forum thread.
    Last edited by Daveembry; 12-30-2021 at 12:02 PM.
    Dave Embry
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  5. #65
    Senior Member Andy's Avatar
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    Default Re: ELT Antenna: vertical or horizontal?

    Quote Originally Posted by Daveembry View Post
    Almost ANYTHING seems to work as long as you add a ground plane. Their bracket doesn’t work.

    In the CubCrafters installation the rear wall of the baggage compartment will act as the ground plane. The problem is that the bracket extends the antenna above the ground plane changing its resonant frequency.

    The ground plane must be at the antenna base to have any chance of the antenna performing as intended. It may be possible to get an acceptable result by blending the antenna base to the rear wall of the baggage compartment with straps that are shorter than 1/4 lambda. Experimenting with that would require suitable test equipment.

    I'm nervous about the single radial solution because I have seen no data for antenna characteristics at 406 MHz.

  6. #66
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    Default Re: ELT Antenna: vertical or horizontal?

    Exactly. As they state, the coax/connector must be on the opposite of the ground plane that the antenna and the bracket doesn't do that.

    https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

    This is the copper foil tape I got. It has adhesive on the back side. I thought I would install it where it mounts between the antenna/bracket side and then have it go back to the rear panel that the bracket is mounted to......and stick it on there with many strips in a radial pattern. The bottom pieces would have to eventually stick to the fabric. I'll install them but wait until after fabric and then stick them to the fabric on the bottom and sides.



    Quote Originally Posted by Andy View Post
    In the CubCrafters installation the rear wall of the baggage compartment will act as the ground plane. The problem is that the bracket extends the antenna above the ground plane changing its resonant frequency.

    The ground plane must be at the antenna base to have any chance of the antenna performing as intended. It may be possible to get an acceptable result by blending the antenna base to the rear wall of the baggage compartment with straps that are shorter than 1/4 lambda. Experimenting with that would require suitable test equipment.

    I'm nervous about the single radial solution because I have seen no data for antenna characteristics at 406 MHz.
    Last edited by Daveembry; 12-30-2021 at 12:05 PM.
    Dave Embry
    "You only live once.......but if you do it right.........once is enough."..

  7. #67
    Senior Member ceslaw's Avatar
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    Default Re: ELT Antenna: vertical or horizontal?

    Quote Originally Posted by Daveembry View Post
    well like I said, I’ve ordered the copper foil in 1” and intend to install it with numerous strips all in all directions per their installation manual. This big piece of the temp shield was just a test (almost a joke!). Almost ANYTHING seems to work as long as you add a ground plane. Their bracket doesn’t work.

    Once I get the foil in and install and test I’ll post more pics here and on my forum thread.
    Consider starting with a single length of foil tape equal in length to the antenna connected to the base of the antenna. I expect that will give you a successful self test result.

  8. #68
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    Default Re: ELT Antenna: vertical or horizontal?

    Well I received the copper 1" tape and installed it and it self tested on the Kannad perfectly. I did install just 1 strip and tested and it worked but I went ahead anyway and installed 3 strips and let them go a little ways beyond the antenna in the lower direction (even though they are not as long as the antenna). Perfect self-tests on the unit.

    The copper strips were self adhesion on the back, so I just cut a 1/2" hole in them and stuck them onto the front side of the bracket where the antenna would go directly against it.....and then stuck it to the back of the baggage compartment. I suppose now it will link that piece of aluminum to the antenna and make a big ground plane.

    So the key does in fact seem to be that the bracket DOES NOT WORK with the Kannad because the coax/connector is not on the opposite side of the ground plane as they state you have to do in the Kannad Installation Manual.

    It doesn't look "pretty" because the foil is thin and having to make it go down from the bracket to the panels makes it a little harder, but it works great.


    Copper strips for ELT antenna on bracket wide.jpg


    Copper strips to elt on bracket close up.jpg


    Copper Strips.jpg

    Quote Originally Posted by ceslaw View Post
    Consider starting with a single length of foil tape equal in length to the antenna connected to the base of the antenna. I expect that will give you a successful self test result.
    Dave Embry
    "You only live once.......but if you do it right.........once is enough."..

  9. #69
    Senior Member Andy's Avatar
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    Default Re: ELT Antenna: vertical or horizontal?

    Quote Originally Posted by Daveembry View Post
    5It doesn't look "pretty" because the foil is thin and having to make it go down from the bracket to the panels makes it a little harder, but it works great.
    Your ELT antenna seems to be mounted lower than the one in my FX-3. Is that as specified in the EX-3 drawings?

    ELT ANT FX-3 0100.PNG
    Last edited by Andy; 01-03-2022 at 11:12 AM.

  10. #70
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    Default Re: ELT Antenna: vertical or horizontal?

    yes. They call for it to be 11.0 - 11.7” from the top of the rear baggage panel. I’d never be able to reach up there from the bottom 5” inspection hole and reach it.

    Quote Originally Posted by Andy View Post
    Your ELT antenna seems to be mounted lower than the one in my FX-3. Is that as specified in the EX-3 drawings?

    ELT ANT FX-3 0100.PNG
    Dave Embry
    "You only live once.......but if you do it right.........once is enough."..

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