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6.3-ii Theory of Operation

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5.0 Transmit Signalling Circuits ................................................................... 10

5.1 Sub-audible Data (PL/DPL)....................................................................... 10

5.2 High Speed Data and DTMF ..................................................................... 11

6.0 Receive Audio Circuits............................................................................ 12

6.1 Squelch Detect .......................................................................................... 12

6.2 Audio Processing and Digital Volume Control........................................... 13

6.3 Audio Amplification Speaker (+) Speaker (-) ............................................. 13

6.4 Handset Audio........................................................................................... 14

6.5 Filtered Audio ............................................................................................ 14

6.6 Discriminator Audio (Unfiltered)................................................................. 14

6.7 Option Board Audio ....................................................................................14

7.0 Receive Signalling Circuits..................................................................... 15

7.1 Sub-audible Data Decoder (PL/DPL) ........................................................ 15

7.2 High Speed Data Decoder......................................................................... 15

7.3 Alert Tone Circuits..................................................................................... 16

216-246MHz Specific Circuit Description

8.0 Receiver Front-End.................................................................................. 17

8.1 Front-End Band-Pass Filter & Pre-Amplifier.............................................. 17

8.2 Mixer and Intermediate Frequency (IF) Section ........................................ 17

8.3 IF IC (U5201)..............................................................................................18

9.0 Transmitter Power Ampliﬁer (PA) 5-25W ............................................... 18

9.1 Power Controlled Stage............................................................................. 18

9.2 PA Stages.................................................................................................. 19

9.3 Directional Coupler.................................................................................... 19

9.4 Antenna Switch.......................................................................................... 19

9.5 Harmonic Filter .......................................................................................... 20

9.6 Power Control............................................................................................ 20

10.0 Frequency Synthesis............................................................................... 22

10.1 Reference Oscillator.................................................................................. 22

10.2 Fractional-N Synthesizer (U3701) ............................................................. 22

10.3 Voltage Controlled Oscillator (VCO).......................................................... 22

10.4 Synthesizer Operation............................................................................... 23

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Motorola GM950E User Manual

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