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Downunder

shark fin antenna

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Is a fin antenna better for a transponder transmission than the "stick and ball" type?

 

 

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Only problem I have had with stick and ball was when I broke it off while washing the underside of the a/c. Fin are stronger.

 

 

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No, they are more robust and expensive. The cheapest version of stick and ball are prone to breaking when washing the plane.

 

 

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So I’ve not seen a shark fin up close.

 

Are they a truly shark fin shaped metal antenna or are they just a stick and ball in a fin shaped plastic cover?

 

 

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this is what the dentist saw[ATTACH=full]61702[/ATTACH]

Sorry can’t work out what that is.

 

Looks like the business end of a fly swatter. 004_oh_yeah.gif.82b3078adb230b2d9519fd79c5873d7f.gif

 

Is that metal or plastic?

 

 

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Pilot dentist buddy X-Rayed one. What you see is the film taped to a window, hanging in the conventional way.

 

The guts of the thing appear to be the connector centre shaft coming down, soldered to a flat perforated pice of metal, roughly the shape of the outer moulding. Radio is a black art, what we see doesnt allways look plausible. GPS patch antennae are another mystery.

 

 

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Ah. Ok. Now I get it. Too cryptic for me.

 

It would be interesting to see the propagation diagram for that. I would have thought it would be crap. Two lateral lobes and nothing front to back. Not what you want in a transponder antenna.

 

But I must be missing something otherwise they would never have got off the design desk.

 

 

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Only problem I have had with stick and ball was when I broke it off while washing the underside of the a/c. Fin are stronger.

 

Yes I have had this problem (along with so many others) - My solutions;

 

  • Spring load the antenna. By this I mean, find a spring that has an internal diameter a tiny bit on the small side. Slightly score shaft ends with course sandpaper. Put a small amount of epoxy into spring (for added security). Screw the broken ends of the antenna into each end of the spring, until the ends meet.You now have a functioning antenna that is resistant to breakage. Mine has been working like this for 4 years. It will break eventually when the spring fatigues
     
  • You can purchase the antenna base quit cheaply - find a nice peace of multi strand copper cable. The cable can have strands removed to fit the antenna base. Solder cable to base. Very carefully cut cable to same length as original antenna. Cover everything with two layers of shrink tube. You now have a home made "rubber ducky" transponder antenna, resistant to breakage, at a fraction of the purchased cost of original (as replacements I have mad up 2 but never used because above works well)
     

 

 

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Stick and ball has worked for years. Local avionics shop said to but a shark fin for the ADS-B requirement, no reason given other than "they work better". Look at the Hz range for the shark, some are greater than others. Now determine if that is important.

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