Tx Audio Circuit; Figure 4-2. Tx Audio Circuit (Uhf1 And Uhf2); Figure 4-3. Tx Audio Circuit (Vhf) - Motorola P100 Series Detailed Service Manual

Controller Theory of Operation: TX Audio Circuit
4.2

TX Audio Circuit

The TX audio circuit consists of MIC/External MIC, LPF, Audio processor IC, and TX Sub-tone
system. For UHF1 and UHF2, refer to Figure 4-2. For VHF, refer to Figure 4-3.
4 Order LPF
(Fc=4KHz)
Mic
(Audio IN)
U501-C,D
TXA1
VR1 Com-
(HPF) pressor
pin4
-6 to +4.5dB/
1.5dB
pin19
Tone IN
(from CPU)
4 Order LPF
(Fc=4KHz)
Mic
(Audio IN)
U501-C,D
TXA1
VR1 Com-
(HPF) pressor
pin4
-6 to +4.5dB/
1.5dB
pin19
Tone IN
(from CPU)
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TX/RX HPF
Pre-
Emphasis
Fc=300Hz
Sub audio
Programmable
-6 to +6dB/
DTA1
LPF
0.5dB
VR5
pin17

Figure 4-2. TX Audio Circuit (UHF1 and UHF2)

TX/RX HPF
Pre-
Emphasis
Fc=300Hz
Sub audio
Programmable
-6 to +6dB/
DTA1
LPF
0.5dB
VR5
pin17

Figure 4-3. TX Audio Circuit (VHF)

Audio Processor IC (AK2347)
Scrambler/
Limiter
Descrambler
U102
2 Order LPF 6 Order LPF
(Fc=300Hz) (Fc=3KHz)
U501-A,B
U502-A
To VCO &
VCTCXO
Audio Processor IC (AK2347)
Scrambler/
Limiter
Descrambler
U102
2 Order LPF 6 Order LPF
(Fc=300Hz) (Fc=3KHz)
U501-A,B
U502-A
To VCO &
VCTCXO
VR2 Splatter SMF
-9.6 to +3dB/ Fc=2.55KHz/
0.2dB 3KHz
pin8
TX AF Amp.
Mod.Adj,
U502-C
U508
VR2 Splatter SMF
-9.6 to +3dB/ Fc=2.55KHz/
0.2dB 3KHz
pin8
TX AF Amp.
Mod.Adj,
U502-C
U508
4-3