Page 1 of 5 12345 LastLast
Results 1 to 10 of 46
  1. #1
    Co-Pilot Riggers's Avatar
    Join Date
    Jul 2010
    Location
    Norfolk
    Posts
    537
    Blog Entries
    1
    Thanks
    28
    Thanked 24 Times in 21 Posts

    Nynja Transponder Antenna mounting

    On the Trig TT21 thread, I mentioned mounting the transponder antenna on a 6" X 6" ground plane, halfway down the fuselage, on the underside, or just inside it:

    TRig Transponder Antenna mounting location.jpg

    I've been advised this might not be the best idea, rendering the occupants vulnerable to toasting by the sideways trons, a la microwave. Better by far, my respected chum says, would be mount it under one of the seats, sticking down into the airflow, with a ~6" X 8" alloy ground plane to afford some protection. I can't be the first to mount such a device on a Nynja - where does everyone else stick it? (No rude answers, PLEASE!)

    The one caveat I have is that my inspector will give me another sound thrashing, if I contravene BMAA doctrine, (HADS/TILS, etc), so I'd like just to get an idea of where I should be looking, (any pics of installations would be much appreciated).

    There's no rush - any time before 14:00 today will do....

    Phil (@ 13:55 today)
    Last edited by Riggers; 04-10-14 at 14:06 PM.


  2. #2
    Test Pilot Paul Dewhurst's Avatar
    Join Date
    Jan 2011
    Posts
    1,047
    Thanks
    2
    Thanked 354 Times in 203 Posts
    Quote Originally Posted by Riggers View Post
    On the Trig TT21 thread, I mentioned mounting the transponder antenna on a 6" X 6" ground plane, halfway down the fuselage, on the underside, or just inside it:

    TRig Transponder Antenna mounting location.jpg

    I've been advised this might not be the best idea, rendering the occupants vulnerable to toasting by the sideways trons, a la microwave. Better by far, my respected chum says, would be mount it under one of the seats, sticking down into the airflow, with a ~6" X 8" alloy ground plane to afford some protection. I can't be the first to mount such a device on a Nynja - where does everyone else stick it? (No rude answers, PLEASE!)

    The one caveat I have is that my inspector will give me another sound thrashing, if I contravene BMAA doctrine, (HADS/TILS, etc), so I'd like just to get an idea of where I should be looking, (any pics of installations would be much appreciated).

    There's no rush - any time before 14:00 today will do....

    Phil (@ 13:55 today)
    talkimg of which - I presume you are working with this http://www.bmaa.org/files/smm_104_4__transponders.pdf as part of your installation process? ( and the other SMM forms for radio etc)

    meeting 4.8 might be tough with aerial under seat?

    Paul


  3. #3
    Co-Pilot Riggers's Avatar
    Join Date
    Jul 2010
    Location
    Norfolk
    Posts
    537
    Blog Entries
    1
    Thanks
    28
    Thanked 24 Times in 21 Posts
    Quote Originally Posted by Paul Dewhurst View Post
    talkimg of which - I presume you are working with this http://www.bmaa.org/files/smm_104_4__transponders.pdf as part of your installation process? ( and the other SMM forms for radio etc)

    meeting 4.8 might be tough with aerial under seat?

    Paul
    Well, er, obviously. <nervous, involuntary cough>

    Looks like it's 'fry, or don't fly', then....
    Last edited by Riggers; 04-10-14 at 19:36 PM.


  4. #4
    Captain Rick Moss's Avatar
    Join Date
    Dec 2009
    Location
    Peak District
    Posts
    1,723
    Thanks
    77
    Thanked 174 Times in 112 Posts
    Yes, but Phil has a Trig, and manufacturers spec overrules.... and section 5.11 of the installation manual states:

     Where practical, plan the antenna location to keep the cable lengths as short as possible and avoid sharp bends in the cable to minimise the VSWR.


  5. #5
    Test Pilot Paul Dewhurst's Avatar
    Join Date
    Jan 2011
    Posts
    1,047
    Thanks
    2
    Thanked 354 Times in 203 Posts
    Quote Originally Posted by Rick Moss View Post
    Yes, but Phil has a Trig, and manufacturers spec overrules.... and section 5.11 of the installation manual states:

     Where practical, plan the antenna location to keep the cable lengths as short as possible and avoid sharp bends in the cable to minimise the VSWR.
    Thanks Rick, its useful to know that's the case with the Trig.

    4.8 does state unless the manufacturer allows. - so its a case of reading all the documentation and the forms Phil!

    for your inspector ( me in this instance!) when you present for final inspection he will need to tick it off against the requirements to submit the SMM forms with the build, so the builder should have done that themselves with any applicable notes, to show the inspector, so it all goes smoothly and there are no 'oh ****' bits that fail the inspection and have to be redone.

    the SMM form also has a link to some additional information on radiation hazards - which also might influence your personal decision where the antenna would be best placed.....!

    Paul


  6. #6
    Co-Pilot Riggers's Avatar
    Join Date
    Jul 2010
    Location
    Norfolk
    Posts
    537
    Blog Entries
    1
    Thanks
    28
    Thanked 24 Times in 21 Posts
    Phew, thank goodness that's all cleared up, then.....

    Think I found the Archbishop of Canterbury's explanation, of 'Salic Law', (the reason why the king of England might claim the French throne), in Laurence Olivier's 1944 wonderful film of Henry V, a little easier to follow!

    Paul: I understand your caution, (much appreciated, on my gonads' behalf!), and will see if some compromise might be possible. To what does the BMAA '1 metre' rule apply? the Trig header unit, on the panel, or its remote processor box, on mine located on the floor, under the stick?


    Any restriction on the size of the ground plane? If not, how about a sheet of aloominum foil, or speed tape, covering a major part of the forward fuselage skin?

    Thanks to all for the dialogue.

    Phil


  7. #7
    Captain Rick Moss's Avatar
    Join Date
    Dec 2009
    Location
    Peak District
    Posts
    1,723
    Thanks
    77
    Thanked 174 Times in 112 Posts
    In the case of the Trig, the 1m rule doesn't apply as above. For clarity, the transponder is the gold coloured remote box; the small unit on the panel is purely a remote control for the transponder (although also includes the altitude encoder I believe). The microwave transmission from the antenna will not penetrate the ground plane, and given the modest length of the antenna, a surprisingly small ground plane will put the occupants in its shadow.


  8. #8
    Co-Pilot Riggers's Avatar
    Join Date
    Jul 2010
    Location
    Norfolk
    Posts
    537
    Blog Entries
    1
    Thanks
    28
    Thanked 24 Times in 21 Posts
    Thanks, Rick.

    Sorry if I'm not the sharpest pencil in box, when it comes to matters avionic...


  9. #9
    Co-Pilot Riggers's Avatar
    Join Date
    Jul 2010
    Location
    Norfolk
    Posts
    537
    Blog Entries
    1
    Thanks
    28
    Thanked 24 Times in 21 Posts
    In case it's of interest, I've come across these photos of a transponder installation on a SkyRanger Classic or Swift: I'm not sure where I got them, since I've been accumulating intel to support my build for some time, but acknowledgements & thanks to whoever's responsible....
    Transponder Ground Plane Assembley-2.jpg Transponder Ground Plane Assy-1.jpg Installed Ground Plane- 2.jpg Installed Ground Plane-1.jpg

    The installed position appears to be just aft of the undercarriage beam, abeam the two seats, so perhaps it's a Trig-based system, with its concessed installation. The ground plane appears riveted to an 'L' section, which shows two attachment points: I'll look at my u/c beam to see if there are correlating existing bolts to pick up. Paul: I'll obviously discuss with you, before I do anything surgical!

    Another (dumb?) question: located beneath the seats will put the antenna between the undercarriage legs and wheels. Won't that upset propagation? Simplistically, if I'm 90 degrees to the monitoring station, will I still be visible?

    Thanks, chaps, [not gender-specific!]

    Phil
    Last edited by Riggers; 05-10-14 at 10:46 AM.


  10. #10
    Captain Rick Moss's Avatar
    Join Date
    Dec 2009
    Location
    Peak District
    Posts
    1,723
    Thanks
    77
    Thanked 174 Times in 112 Posts
    Hi Phil; to my mind that ground plane looks a little over-engineered, as the reality is that from an rf perspective, tinfoil is an adequate material. Durability and ease of mounting means that I have always used .6 or .8mm aluminium. Given the fibreglass underside of your aircraft, I'd suggest the simply drilling a hole where you wish the antenna to be, and then assembling it with the ground plane between the fibreglass and the backnut of the antenna will be a perfectly adequate solution, possibly with a small spot of silicone on each corner to eliminate any possible vibration resonance from a single central mounting.

    The pictures you show would not be my chosen location, only because there is a direct line from the antenna to the occupants without a ground plane in between.

    The UC legs have never proven to cause reception problems for me (Skyranger classic, antenna beneath passenger seat), although in theory they possible could. The location shown above could potentially have the exact same issue, just at a different angle to the interrogating station. Short of mounting it on an undercarriage leg, I think this is unavoidable, but also unnoticeable.

    Happy to be corrected on all the above.... Based ok experience.


Similar Threads

  1. AirMagic Vee Rabbit Antenna
    By oldbaldyman in forum Microlight Technical
    Replies: 39
    Last Post: 14-01-17, 22:23 PM
  2. Nynja Panels
    By Riggers in forum Sky Ranger
    Replies: 196
    Last Post: 13-06-16, 18:34 PM
  3. Antenna ?
    By Ronny Larsson in forum Microlight Discussion
    Replies: 46
    Last Post: 14-06-11, 22:53 PM
  4. How to use a transponder.
    By Polski in forum Microlight Technical
    Replies: 9
    Last Post: 12-12-09, 19:22 PM
  5. Mode S transponder
    By Bob T in forum Microlight Discussion
    Replies: 5
    Last Post: 01-12-09, 20:16 PM

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •