The SR-50 connectors (CP-50 in cyrillic) are Russian-made 50 ohm RF (Radio Frequency) connectors for coaxial cables.
Some of the CP-50 connectors are versions of the 50 ohm BNC connector. They have slightly different dimensions as a result of converting from imperial to metric measurements, but are normally compatible with BNC.
There are many different sizes and constructions of CP-50 connectors, depending on the numbers and letters after the impedance value (50 ohms in this case), most of which do not resemble the BNC connector. "СР" (соединитель радиочастотный) simply means "Radio Frequency Connector". The CP 50-164 for example is a much larger high power connector, designed for >3000W and closer in appearance, but not compatible with an N or UHF type. The various letters after type number (see below) refer to the dielectric material used. Photos of the '164 with teflon dielectric are here [1]
Breakup of the SR Connector type number:
For instance the type number "СРГ-50-312ФВ" means:
- СР (SR) = соединитель радиочастотный (Radio Frequency Connector)
- Г (G) = герметичный (Hermetically sealed) - Normal version is without the 3rd letter.
- 50 or 75 = Design impedance of the connector (ohms)
- 312 = Connector type number
- Ф (F) or П (P) = Dielectric material - Ф = фторопласт (PTFE/Teflon), П = полиэтилен (Polyethylene)
- В (V) = всеклиматическое исполнение по ГОСТ В 20.39.404-81 (Fulfils requirements of the Russian ГОСТ standardization agency)
Here you can find a listing of SR connectors of one Russian manufacturer (in Russian): [2]
And here is an extended specification book of SR connectors (in Russian): [3]