Why aren't 75 ohm BNC connectors used for SPIDF or even L or R outputs?

[goraman]

There is a BNC variant having a characteristic impedance of 95 Ohm, and used for video connections in the aerospace industry.

https://en.wikipedia.org/wiki/BNC_connector

I was probably wrong 95 ohm sounds right, It has been awhile so my memory is from 20 years ago.
I was at a flea market and bought a coffee can full of Amphenol PL259 silver plated connectors new, for $10.00!
Same guy had boxes of 50,75 and 95 Amphenol BNC connectors and it was the first time I had seen any thing over 75 ohm so I asked what they where for and he said NASA video.

[Barry]

I was probably wrong 95 ohm sounds right, It has been awhile so my memory is from 20 years ago.
I was at a flea market and bought a coffee can full of Amphenol PL259 silver plated connectors new, for $10.00!
Same guy had boxes of 50,75 and 95 Amphenol BNC connectors and it was the first time I had seen any thing over 75 ohm so I asked what they where for and he said NASA video.

Until now I hadn't heard of 95 Ohm BNC connectors (and I worked in electronics R&D for nearly 30 years), which is why I clicked on the Wiki link cited to check.


There is a little confusion on the inter-matability between 50 Ohm and 75 Ohm connectors. If the dielectric support insulation is maintained, since all BNCs have the same outer diameter, 75 Ohm versions have a smaller centre conductor than the 50 Ohm types. This means that a 50 Ohm plug, having a larger diameter centre pin will, if mated with a 75 Ohm socket, damage the latter because the socket will have a smaller diameter centre recepticle.

However, there are some designs of 75 Ohm BNCs that forgo the centre support dielectric. This is possible because most BNC connectors use a support dielectric having a relative permittivity of ~ 2.3, and since the characteristic impedance varies inversely as the root of the permittivity (that is ~ 1.5), removing the support dielectric means a 75 Ohm version can have the same dimensions as that of a 50 Ohm version. So if these two are mated, no damage will occur. One has to look carefully to check if this is possible.

[goraman]

Until now I hadn't heard of 95 Ohm BNC connectors (and I worked in electronics R&D for nearly 30 years), which is why I clicked on the Wiki link cited.

I don't think they are in wide circulation.