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Thread: Transponder aerial mouting.

  1. #1
    Member
    Join Date
    Sep 2010
    Location
    Scotland (Glasgow)
    Posts
    42

    Transponder aerial mouting.

    We
    have a non functioning tx on our aircraft which Iím in the process of sorting
    out (so we can fly during the commonwealth gamesÖ..)

    The
    tx is installed complete with aerial, but the fuse has been pulled. Looking at the manual (itís an old Garmin GTX
    320A), it clearly states in bold letters that the aerial must be more than 1m
    (3ft) from the tx housing.

    On
    our aircraft its only about 1.5ft from the tx housing, so I imagine this may be
    why the fuse has been pulled.

    What
    I now need to do is move the aerial and get the whole lot tested and signed
    off.

    My
    question is, how (and where) do folk put their tx aerials on Skyrangers?

    The
    radio aerial is above the cockpit at the edge of the polycarbonate screen/wing
    root, so it canít go anywhere near there.

    As
    most of our wiring is beneath the seats/false floor, I was thinking of running
    it half way down the lower fuselage and poke it through the Dacron, but how do
    I then affix it in place? Will need a
    ground plane (flat bit of metal) behind it as the fuselage isnít metal on
    Skyranger?

    Can
    anyone post up photos of their installations?

    Cheers

    Andy

  2. #2

    Transponder aerial mouting.

    Hi Andy
    I have had a Trig T21 transponder installed for a few years now and it works flawlessly. The XPDR antenna is mounted on a rectangular aluminium plate around 150 to 200 mm square fastened via a short length of angle to the rear of TU9 (undercarriage X member) Using the existing TU27 (X brace) bolts. The antenna then pokes out below through the lacing and a small hole in the velcroed flap. I originaly had the comms antenna mounted in the standard top rear corner of the cabin triangle with a hand held Icom located between the seats and an Airzone intercom on the cross tube just below the luggage hammock. With this set up there was just a very slight click. I have since upgraded the comms and now have a panel mounted Funkwerk ATR833 radio and use its internal intercom with a belly mounted antenna located just in front of the rear fuselage cross brace. Even though this is now closer to the XPDR antenna there is no interference and the clicks have gone. I will see if I can find the photos.
    Mike

  3. #3
    Senior Member 100 Club
    Join Date
    Mar 2009
    Location
    Essex, close to the infamous Stansted Zone
    Posts
    475

    Transponder aerial mouting.

    Hi Andy

    See the discussion about transponder antenna installation here:

    http://forums.bmaa.org/default.aspx?f=32&m=44334&g=48050#m48050

    Regards

    Alan

  4. #4

    Transponder aerial mouting.

    Andy
    I did post a series of photos of the antenna instalation in the files section of the Skyranger group but I can't seem to find them on the new Yahoo setup. However if you paste the following link into your browser you can download them.
    https://groups.yahoo.com/neo/groups/skyranger/files/TT21%20Transponder/Alternative%20Transponder%20Antenna/

    Mike

  5. #5
    Member
    Join Date
    Sep 2010
    Location
    Scotland (Glasgow)
    Posts
    42

    Transponder aerial mouting.

    Many thanks guys, now all I need to do is get some new coax cable and some aluminium sheet to cut up :thumbup:

    Cheers

    Andy

  6. #6

    Transponder aerial mouting.

    Andy
    I don't know if you have the installation instructions for your XPDR. If not it may be worth following yhe Trig advice as frequency and power levels will be the same.
    1) Keep coax short and use RG 400 or better to minimize losses.
    2) Ground plane - Avoid circles and use square or rectangle of minimum size 120mm per side but bigger is better up to about 700 as after that no significant improvement.

    Mine is about 200 and works fine. Wavelength is 275 mm so on a square the centre to corner dimension for the 120 square is just over 1/4 wave hence the limit.
    Mike

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