Friendcom FC301 RSSI signal

The Friencom FC301 radio provides an RSSI signal output but the manual does not specify the relationship between RX signal strength and the voltage on the RSSI signal output.

I made these measurements by feeding an RF from a signal generator directly into the antenna input of the radio and measuring the RSSI output.

Signal Input RSSI
1 0.2uV 620mV
2 0.4uV 660mV
3 0.8uV 738mV
4 1.6uV 835mV
5 3.2uV 1.0V
6 6.3uV 1.166V
7 12.6uV 1.338V
8 25uV 1.503V
9 50uV 1.637V
9+10dB 160uV 1.924
9+20dB 500uV 2.200
9+30dB 1.6mV 2.344
9+40dB 5.0mV 2.415