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Transponder: TNC. ADSB/Radio: BNC. Why?

Steve Crewdog

Well Known Member
Patron
Just curious, I've got a Dynon 261 transponder that uses a TNC connector, while the Dynon ADSB and Garmin GTR-200 radio uses BNC connectors. Is there a reason/convention they're that way, and the transponder does not use a BNC?


Thanks
 
I was told it was to prevent you inadvertently connecting a comm radio to a transponder antenna. Comm radios can be easily damaged if you try to transmit without a properly matched antenna.
 
I was told it was to prevent you inadvertently connecting a comm radio to a transponder antenna. Comm radios can be easily damaged if you try to transmit without a properly matched antenna.

That's sound engineering. Ref. NASA-STD-8739.4

Precautions shall be taken to prevent the mismating of connectors, caused by interchanging or by
reversing, through one of the following techniques:
7.1.1 Use of constraints that locate similar connectors built into interconnecting cables and harnesses so they cannot be interchanged (Requirement).
7.1.2 Selection of different sizes for connectors to be located adjacent to each other (Requirement).
7.1.3 Polarization or dissimilar keying of adjacent, similar connectors (Requirement).
7.1.4 Ensure clarity in marking and coding connectors (Requirement).
7.1.5 Use of confidence loop circuits to check out proper mated positions (Requirement).
 
Also, the transponder output is what, 10 orders of magnitude more power than a comm transmitter. So, a lower loss connector makes a difference with the higher wattage transmitter in a transponder...
 
Also, the transponder output is what, 10 orders of magnitude more power than a comm transmitter.

Uh, no. More like two orders of magnitude. And the transponder output is a short pulse, so the energy loss is pretty small. 10 orders of magnitude means ten billion.
 
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