Table of Contents
6.3-ii Theory of Operation
Paragraph Page
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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