[Elecraft] K3 S-meter reading and coax input or antenna voltage ?

[Phil Hystad]

If I had an S-meter reading, S9 for example, on my K3, what could I infer about the voltage level of that signal at the Coax input to my K3?

A table I found on the Internet for singals below 30 MHz says that an S-9 meter reading is a signal of 50-microvolts but where in the system is that registering 50 microvolts.  At the input the K3 or some other circuit within the K3?

Thanks -- just mostly curious about this and the connection between S-meter reading and actual signals input to the receiver.

73, phil, K7PEH