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Thread: ELT Antenna Location

  1. #1
    Senior Member HighWing's Avatar
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    Default ELT Antenna Location

    I spent the bucks for the 406 Mhz ELT and now am trying to find a spot at least 30 inches from the Com antenna to mouint it's antenna and am frankly baffled. My first Model IV had the ELT antenna placed internally at the side and behind the baggage sack. I wonder if the money spent to talk to satellites will be blown if an internal placement reduces signal output significantly. The only other place I can think of is on the turtle deck near the side and immediately aft of the flaperon horn. This would require disconnecting the antenna every time I remove the turtledeck, but not a difficult task as it is within reach of the door. Thoughts would be welcome.
    Lowell

  2. #2
    Senior Member Dave S's Avatar
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    Default Re: ELT Antenna Location

    Lowell,

    Also got the 406.

    In our series 7 - the ELT antenna was placed inside the baggage area on the starboard side. Like in your first IV.

    I had the same question you have with proximity to the com antenna; and, my DAR/EAA tech counselor suggested inside the fuselage if at all possible in a fabric covered airplane - logic being if the ELT is ever needed and it is outside on the top or bottom - you have 1/2 a chance it won't work anyway because the plane will be either on its top or bottom with the antenna busted - you can pick the location of the antenna, but not necessarily how an off airport landing will leave one - upside or down side.

    Personally I don't believe a person can ever count on 100% functionality of any ELT in the event of an OOPS - it is just a matter of probability, however, I liked the inside the baggage bay location because there is some protection for the antenna no matter which way is up and a fabric airplane with space between the steel tubing so it might work if needed. Also installed an insulating sleeve over the antenna to prevent an accidental shorting out.

    Mounting location aside, the theory on the 406 is that no matter what - there is a better chance of getting that line of light necessary for it to work compared to a ground based system.

    Empirically, any particular location would have to be tested; and, I do not know of anyone who has done that.

    Sincerely,

    Dave S

  3. #3
    Senior Member jrevens's Avatar
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    Default Re: ELT Antenna Location

    Lowell,

    My buddy Stan has a mod. IV with the antenna located inside the fuselage, along side the baggage area on the pilots side. He doesn't monitor this forum very often, so I'm going to try to describe his experience - I hope he'll add any necessary corrections. He installed a new ACK 406 mhz unit last year. During his trip to OSH, while staying with friends, his airplane was exposed to the worst rain storm & winds while tied down, that he had ever experienced. Long story short, the ELT was somehow triggered when rain got into the cockpit & got the remote indicator/switch unit wet. It worked very well from that point on, as he (or a relative?) got a call from the Air Force in a very short period of time.

    I'm installing mine in basically the same position, but on the passengers side, on my mod. 7SS.

    IMG_0762.jpg
    John Evens
    Arvada, CO
    Kitfox SS7 N27JE
    EAA Lifetime
    Chap. 43 honorary Lifetime

  4. #4
    Senior Member HighWing's Avatar
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    Default Re: ELT Antenna Location

    I do appreciate these responses. Actually at this point I am trying to create something that a DAR or the FAA will approve. Both these posts are to that point. I know Stan very well and his experience is worth a lot. It will go inside. I put my first airplane down in a precautionary landing that unfortunately destroyed it and I recall while still at the site a uniformed person asking where the ELT was so he could turn it off - it was screaming at the helicopter overhead. The antenna was inside. That is the way I will go again.
    Thanks,
    Lowell

  5. #5
    Senior Member jtpitkin06's Avatar
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    Default Re: ELT Antenna Location

    My aircraft has the speed tail so there was room in the vertical stab to install the ELT antenna up through the lightening holes. I made an aluminum plate the same size as the mounting rib as a counterpoise for the antenna.

    I mounted the ELT on a cross member and diagonal brace just aft of the baggage sack on my Model 7.

    I used the existing holes in the tray and was able to get a good fore and aft alignment using Adel Clamps. The diagonal brace was a bit too high for the ELT so I used some stand offs made with a piece of 3/8 aluminum tube with the mounting bolt down the center of the tube.



    It will take more than a few g's to break it loose and that will certainly be enough to set it off. Hard to tell in the picture but there are four bolts holding the tray to the fuselage.


    With the tail on the ground I can reach the ELT for battery service or removal. I just unzip the velcro bag sack and it's right there.


    John Pitkin
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    Senior Member HighWing's Avatar
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    Default Re: ELT Antenna Location

    Thanks again for the posts. As I look at the pictures, mine is now located essentially where jrevens' is. I took it a bit lower and made a mount that clamps between the two tubes seen at the side, but closer to the bottom of the V.

    John, it looks like you have lots of extra coax cable. Mine came quite short with the caution to put the antenna as close as possible to the unit. That and the fact I was already covered eliminated many other possibilities. One thought about the mounting, I bought the AmeriKing and as with the one mounted in the first airplane there is a lot said in the manual about a strong G resistant mounting then giving four 4-40 screws to mount it. I suppose that once the inertia switch trips the satellite doesn't really care where the ELT is as long as the antenna remains connected. I also shied away from adel clamps. I mounted mine on a welded up support that clamps to the carry through tube between the lift strut attachments and then went big time to four 6-32 screws. As I was doing this, my rocket scientist friend was here and I mentioned the smaller screws and he rolled his eyes and wanted to see my calculator.
    Lowell
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    Senior Member jtpitkin06's Avatar
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    Default Re: ELT Antenna Location

    Lowell, I doubled the fudge factor and Finagle's constant (2FF+2Fk) and mounted the ELT with 10-32 hardware. Yeah, 6-32 is a bit small in my book. [rolling eyes in unison with rocket scientist] My tray had #8 size holes.
    What the heck, if I hit hard enough to rip the thing loose it probably won't be survivable, anyway.

    The extra coax is part of the certification package for the TSO. I must use the factory length coax and the factory antenna for the TSO to be valid. The manufacturer says to simply coil up the excess coax. There's a lot more in the plane with the antenna in the v-stab. The other wire to the ELT is the remote activation to the cockpit wiring. (Also required if not in reach from the pilot seat.).

    John

  8. #8
    Senior Member HighWing's Avatar
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    Default Re: ELT Antenna Location

    Quote Originally Posted by jtpitkin06 View Post
    [rolling eyes in unison with rocket scientist] My tray had #8 size holes.
    John
    I just reread my post and true I wasn't sufficiently clear. The rocket scientist is back this evening using my hanger to rib stitch his Stearman's aileron that suffered some significant hangar rash that required some rib repair and recovering. Anyway, the reason he wanted to see the calculator was to prove to me that the 4-40 screws in the installation kit were adequate. I suppose from his perspective - extreme engineering and weight saving to the Nth degree - they are, but went to the 6-32 as they are countersunk in the bottom of the tray and larger than that the four heads of the screws would have been the only things contacting the bottom of the ELT.
    Lowell

  9. #9

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    Default Re: ELT Antenna Location

    When running your coax from the elt to the antenna, if you have enough cable, it doesnt hurt to leave exta cable between each cable tie or mounting clamp. This will allow the cable room to stretch instead of breaking if the fuselage were to break apart.

    Just my two cents!~Cain B

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    Default Re: ELT Antenna Location

    Hi,
    I am having false ELT alarms from my new ACK 406 ELT going off when I turn on my Narco Transponder with added UAvionix ADS-B in-out. I built my Kitfox 4 in 1993 and the ELT mount is behind the passenger seat (never had a problem with my old ELT). ELT antenna is behind Pilot on 16" ground plane inside fuselage. Transponder antenna is very close to ELT unit about 12".

    The techs at ACK say I need to move transponder antenna at least 3' away from the ELT unit because the new satellite technology is much more sensative to RFI. They also suggested wrapping the ELT unit in tinfoil to protect it from RFI. This worked but not all the time.

    Since ADS-B out is pretty new any thoughts? I will post the results of my moving the transponder antenna soon.

    Cheers,
    Kirby

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