Found on the rear of an old (1970s) Sanyo monitor. It's not standard cable/co-ax, it's larger and beefier. It's used here for a composite signal.

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Thanks for any pointers.

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    \$\begingroup\$ That connector is not obsolete - it is commonly used as an antenna connector on CB and VHF marine radios. \$\endgroup\$ Sep 14 at 18:14

That looks like an SO239 UHF connector.

That's the socket that goes with the PL259 plug.

The term "UHF connector" is somewhat misleading.

It was developed in the 1930s. Back then, UHF meant "over 30MHz." These days, UHF is 300 MHz to 3GHz.

  • 1
    \$\begingroup\$ For a discussion of how far SO239 is from being a modern-meaning UHF connector: an answer on ham.stackexchange.com. \$\endgroup\$ Sep 14 at 18:33
  • \$\begingroup\$ True. I had it on my marine VHF and CB, but the antenna and cable was 50 ohm (RG-58). You can see on the case that is meant to connect a 75 ohm impedance. As @MarcusMüller say in other post, this connector probably doesn't meet a 50 nor 75 ohm characteristics impedance, they just made a connector as is. \$\endgroup\$ Sep 14 at 18:56
  • 2
    \$\begingroup\$ My oscilloscope (built in 1965) has SO239 sockets. The original probes had PL259 plugs on them. I use BNC to SO239 adapters and modern oscilloscope probes. \$\endgroup\$
    – JRE
    Sep 14 at 19:05
  • 3
    \$\begingroup\$ Nice thing about SO239, you can stick banana plugs in the center pin. Other than that, horrible connector. \$\endgroup\$
    – qrk
    Sep 14 at 22:55
  • \$\begingroup\$ My brand-new HF radio (3–50MHz) uses this connector for the antenna. \$\endgroup\$ Sep 15 at 3:11

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