3.5.4 2
nd
Intermediate Frequency Circuit
The 1
st
IF signal is added to IC3 and converted to 2
nd
IF signal. The 2
nd
IF signal goes
through F2 and amplified in the IC3 and then through discriminator CD1 and the
demodulated AF signal is output from IC3.
3.5.5 Low Frequency Circuit
The AF signal demodulated in the IC3 goes through the de-emphasis circuit consisting of
operational amplifier IC4(A) and R127 and C45. A 3 stage active HPF consisting of
IC4(B) ,C48,C49 C50,R23,R24 and R25 is used to reject AF signal below 300Hz. The AF
signal from the 3-stage HPF goes through AF Volume VR301 and is input to the speaker
amplifier circuit IC9.
3.5.6 Audio Muting Circuit
The Q18 to mute the audio is controlled by input of squelch’s BUSY signal and the
mute output of the CPU(IC201).
3.5.7 WX Alert Detection
The tone selector IC10 detects the 1050Hz alert tine if it is contained in the
re-modulated AF and WX alert tone will be output from the speaker.
3.5.8 DSC Signal Treatment
If the re-modulated signal arriving is a DSC signal, it is input to MODEM IC(IC11) as an RX
MODEM signal, and converted to digital signal. Undergoing the treatment in the CPU circuit,
this digital signal changes the operation state to DSC mode.
