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

[Steve SR]

Just curious, I've got a 261 transponder that uses a TNC connector, while the 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

 

[John Bright]

I imagine it's because the transponder is in what is referred to as the microwave frequency range of 300 MHz to 300 GHz and as Wikipedia says: TNC "has better performance than the BNC connector at microwave frequencies".

TNC connector - Wikipedia

en.wikipedia.org

BTW, these connectors were invented by Mr N and Mr C. They came up with Bayonet NC and Threaded NC connectors.

 

[Rhino]

BNC doesn't perform as well above 4 Ghz, but it's usually just a manufacturer preference. TNC also makes a more secure connection than BNC.

 

[GalinHdz]

I imagine it's because the transponder is in what is referred to as the microwave frequency range of 300 MHz to 300 GHz and as Wikipedia says: TNC "has better performance than the BNC connector at microwave frequencies".

The Bayonet Navy Connector (BNC) was primarily designed for up to VHF frequencies while Threaded Navy Connector (TNC) was primarily designed for UHF frequencies and above, hence the difference in performance. Once you get to SHF then you need to use waveguides in place of connectors and coax.

And you do NOT want to have the same connectors to adjacent antennas cut to different RF band(s). Comm radios are a very different RF band than Xponder so this way it is significantly harder to connect the wrong antenna a transmitter.