The telemetry scanner program is what you would use. You can see on the left side of the display it shows the signal strength. Once you enable the telemetry output on the RFU then that information will show up.
You have to RECORD a session in order to get a data file. You select the location that the file will be stored.
Also, the statement above about only the original 8/10 channel and RFU supporting telemetry is incorrect! The Nano receivers also support telemetry, but they do not provide a battery voltage, all other receivers do.