Tx Audio Circuit; Figure 2-5. Tx Audio Block Diagram (Uhf1 And Uhf2); Figure 2-6. Tx Audio Block Diagram (Vhf) - Motorola CP185 Basic Service Manual

Theory Of Operation: Major Assemblies
2.2.5

TX Audio Circuit

The TX audio circuit is comprised of microphones, LPF, Audio Processor IC, and TX Sub-tone
system.
4 Order LPF
(Fc=4KHz)
(Audio IN)
U501-C,D
TXA1
VR1
(HPF)
pin4
-6 to +4.5dB/
1.5dB
Tone IN
(from CPU)
4 Order LPF
(Fc=4KHz)
(Audio IN)
U501-C,D
TXA1
VR1
(HPF)
pin4
-6 to +4.5dB/
1.5dB
Tone IN
(from CPU)
Mic
TX/RX HPF
Com- Pre-
pressor Emphasis
Sub audio
Programmable
DTA1
LPF
pin19

Figure 2-5. TX Audio Block Diagram (UHF1 and UHF2)

Mic
Com- Pre-
pressor Emphasis
Sub audio
Programmable
DTA1
LPF
pin19

Figure 2-6. TX Audio Block Diagram (VHF)

Audio Processor IC (AK2347)
Scrambler/
Descrambler
Fc=300Hz
U102
2 Order LPF
-6 to +6dB/
(Fc=300Hz)
0.5dB
VR5
pin17
U502-A
Audio Processor IC (AK2347)
TX/RX HPF
Scrambler/
Descrambler
Fc=300Hz
U102
2 Order LPF
-6 to +6dB/
(Fc=300Hz)
0.5dB
VR5
pin17
U502-A
Limiter VR2 Splatter
-9.6 to +3dB/ Fc=2.55KHz/
0.2dB 3KHz
6 Order LPF
(Fc=3KHz)
Mod.Adj,
U508
U501-A,B
To VCO &
VCTCXO
Limiter VR2 Splatter
-9.6 to +3dB/ Fc=2.55KHz/
0.2dB
6 Order LPF
(Fc=3KHz)
U502-C
U501-A,B
To VCO &
VCTCXO
2-7
SMF
pin8
TX AF Amp.
U502-C
SMF
3KHz
pin8
TX AF Amp.
Mod.Adj,
U508