Motorola EP350

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Controller Theory of Operation: TX Audio Circuit 4-3

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.

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

Figure 4-3. TX Audio Circuit (VHF)

VR1

(HPF)

Limiter

Scrambler/

Descrambler

Splatter SMF

TX/RX HPF

TXA1

-6 to +4.5dB/

1.5dB

-9.6 to +3dB/

0.2dB

Audio Processor IC (AK2347)

Tone IN

(from CPU)

VR5

Sub audio

Programmable

LPF

pin4

pin17

pin8

U102

-6 to +6dB/

0.5dB

Fc=300Hz

VR2

Pre-

Emphasis

Com-

pressor

DTA1

pin19

To VCO &

VCTCXO

2 Order LPF

(Fc=300Hz)

U502-A

Mod.Adj,

6 Order LPF

(Fc=3KHz)

U501-A,B

U508

TX AF Amp.

U502-C

4 Order LPF

(Fc=4KHz)

U501-C,D

Mic

(Audio IN)

Fc=2.55KHz/

3KHz

VR1