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Thread: ELT Antenna: vertical or horizontal?

  1. #41
    Senior Member ceslaw's Avatar
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    Default Re: ELT Antenna: vertical or horizontal?

    Quote Originally Posted by Andy View Post
    Your MFJ image with radial added shows R=70, X=0, SWR=1.0. That is an inconstant data set for a 50 ohm system. Was the analyzer configured for 75 ohm measurements? It's a long time since I used an MFJ analyzer and I don't remember if it had the ability to switch between 75 and 50 ohm measurements.
    Good commentary Andy. Regarding the foregoing, a bit of fine tuning led to the following result. Better?

    IMG_1872.jpg

  2. #42
    Senior Member ceslaw's Avatar
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    Default Re: ELT Antenna: vertical or horizontal?

    Quote Originally Posted by Andy View Post
    I followed up with Orolia by asking these questions:
    ". . . The installation you are describing is not optimal, although it is acceptable. . . .
    Without GPS the ELT will be localized within 1 NM within 10 to 30 minutes.
    If the GPS works, the ELT will be localized within 120 metres within 1 to 5 minutes."
    Good information Andy. My take away is that the GPS does not add a lot to the overall rescue situation, so perhaps the degraded performance with the unit under the seat is of lesser significance. If one is really concerned, moving it to the location in the baggage compartment may be an option to enhance the internal GPS performance as well as the other reasons noted in a prior post.

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    Senior Member Andy's Avatar
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    Default Re: ELT Antenna: vertical or horizontal?

    Quote Originally Posted by ceslaw View Post
    My take away is that the GPS does not add a lot to the overall rescue situation, so perhaps the degraded performance with the unit under the seat is of lesser significance. If one is really concerned, moving it to the location in the baggage compartment may be an option to enhance the internal GPS performance as well as the other reasons noted in a prior post.

    I think it could be significant in a rescue situation. Let's say the engine fails over unlandable terrain. You do what you can to start the engine then announce your situation on whatever VHF frequency you think appropriate. You also activate the ELT. Two minutes later you impact the terrain, are incapacitated, and the ELT is damaged so it does not transmit.

    Your only hope that the ELT will help in your rescue is that COSPAS/SARSAT located your position in the 2 minutes it (the ELT) was transmitting before it was disabled. I think that chance is maximized if the ELT broadcast your GPS position as soon as it was turned on. Best chance of that seems to be if the ELT was receiving a valid GPS position over RS-232 bus when it was activated. Second best hope is that GPS reception was good enough for the internal GPS to establish a position before the ELT is disabled. With no GPS position and only a 2 minute transmission you may not be located at all.

    Probably painting a worse case scenario but I'm tempted to give my ELT an RS-232 GPS data input. The GDU only has 5 RS-232 ports and all mine are used. I'm considering using a completely independent GPS receiver that would remain powered with Avionic bus not active.

  4. #44
    Senior Member ceslaw's Avatar
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    Default Re: ELT Antenna: vertical or horizontal?

    Andy:

    I don't disagree. That is certainly a valid theoretical scenario. My thought is it boils down to the individual pilots risk assessment and safety comfort level.

    I am strongly leaning to moving the Kannad to the baggage area where the GPS should put out a good signal.

    Does the Kannad have the ability to input a GPS signal from an external source?

    It would seem a benefit to keeping the internal GPS is it would presumably continue to transmit a location signal after a crash in which the aircraft's primary electrical system is knocked out.

    Looking forward to what you learn when testing the aft location for GPS reception.

    So much time and thought has been spent on this topic which hopefully will never be needed.

  5. #45
    Senior Member Andy's Avatar
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    Default Re: ELT Antenna: vertical or horizontal?

    Quote Originally Posted by ceslaw View Post
    Does the Kannad have the ability to input a GPS signal from an external source?
    The installation manual shows that an external GPS can be connected using the DIN12 connector. I can't find the specification for the required GPS signal format so more research would be needed. It's low on my priority list.

  6. #46
    Senior Member Andy's Avatar
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    Default Re: ELT Antenna: vertical or horizontal?

    Quote Originally Posted by ceslaw View Post
    Looking forward to what you learn when testing the aft location for GPS reception.
    I ran that test this morning. I used three antenna locations with aircraft heading East (previous seat evaluation images were with aircraft heading South) -

    1. On standard fuselage mount over rear seat
    2. In center of the forward "brain box" mounting bracket. This location is partially blocked by the aft edge of the turtle deck.
    3. In center of the aft "brain box" mounting bracket. This location has a good view of the sky except forward where low satellites would be blocked by the turtle deck.

    Here are the screen captures:

    Location 1:
    loc 1.PNG

    Location 2:
    loc 2-1.PNGloc 2-2.PNG

    Location 3:
    loc 3-1.PNGloc 3-2.PNG

  7. #47
    Senior Member ceslaw's Avatar
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    Default Re: ELT Antenna: vertical or horizontal?

    Andy:

    Excellent information. Thank you for posting. That would tend to confirm the baggage compartment aft of the turtle deck is much better for GPS reception than under the pilot's seat. I may well relocate the Kannad to that location.

  8. #48
    Senior Member Andy's Avatar
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    Default Re: ELT Antenna: vertical or horizontal?

    Quote Originally Posted by ceslaw View Post
    Andy:

    Excellent information. Thank you for posting. That would tend to confirm the baggage compartment aft of the turtle deck is much better for GPS reception than under the pilot's seat. I may well relocate the Kannad to that location.
    Don't forget that if you can't reach the switch you'll need to install the remote panel for the ELT. That's not fitted on the FX-3.

    I don't plan to re-locate my ELT but will investigate an RS-232 GPS data feed, perhaps as a winter project.

  9. #49
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    Default Re: ELT Antenna: vertical or horizontal?

    After all those very interesting posts, I will keep the Kannad under the pilot's seat, and will consider a GPS data feed like Andy. The antenna will remain in the fuselage, but with an improved ground plate as suggested by Chuck and Dave.
    I'll keep you informed later. At the moment I start the covering.

  10. #50
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    Default Re: ELT Antenna: vertical or horizontal?

    95246937-6B46-478D-819C-17A9F0055321.jpg

    “The ground plane must be connected to the shield of the antenna connector.”
    Dave Embry
    "You only live once.......but if you do it right.........once is enough."..

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