DANIELS
ELECTRONICS LTD.
TM
VHF Enhanced Extra Wideband Receiver Instruction Manual IM10-VR3H040-AB
3-3
Graph of the RSSI Output Voltage versus RF Signal Level.
-120.0
-100.0
-80.0
-60.0
-40.0
RF SIGNAL LEVEL (dBm)
4.70
3.70
2.70
1.70
0.70
RSSI OUTPUT VOLTAGE (Vdc)
MT3RXM4
Note: Standard input signal used (1kHz tone, 3 kHz deviation).
3.1.7
Audio Processing
Recovered audio from pin 9 of U2 supplies both audio and squelch circuitry. Operational
amplifier U18A is AC coupled to the recovered audio line providing low pass filtering with a
cutoff frequency of approximately 8 kHz, together with amplification of the recovered audio
signal. The output of U18A provides a flat audio response which can be routed, via jumpers
JU10, JU11 and JU12, through a voice band filter and/or connected directly through the audio
squelch gate U7.
Operational amplifier U18B provides unity gain, direct DC coupling of the discriminator output
which is enabled by installing jumper JU25 and removing jumper JU37.