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Table of Contents
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4.4 TX Secure Audio (optional) ....................................................................... 11
5.0 Transmit Signalling Circuits ................................................................... 12
5.1 Sub-audible Data (PL/DPL) ....................................................................... 12
5.2 High Speed Data ....................................................................................... 13
5.3 Dual Tone Multiple Frequency (DTMF) Data............................................. 13
6.0 Receive Audio Circuits............................................................................ 14
6.1 Squelch Detect .......................................................................................... 14
6.2 Audio Processing and Digital Volume Control ........................................... 15
6.3 Audio Amplification Speaker (+) Speaker (-) ............................................. 15
6.4 Handset Audio ........................................................................................... 16
6.5 Filtered Audio ............................................................................................ 16
6.6 RX Secure Audio (optional) ....................................................................... 16
7.0 Receive Signalling Circuits..................................................................... 17
7.1 Sub-audible Data Decoder (PL/DPL) ........................................................ 17
7.2 Alert Tone Circuits ..................................................................................... 17
Midband (66-88MHz) Specific Circuit Description
8.0 Receiver Front-End.................................................................................. 19
8.1 Front-End Band-Pass Filter & Pre-Amplifier .............................................. 19
8.2 Mixer and Intermediate Frequency (IF) Section ........................................ 19
8.3 IF IC (U2201) .............................................................................................. 20
9.0 Transmitter Power Amplifier (PA) 5-25W ............................................... 20
9.1 Power Controlled Stage............................................................................. 20
9.2 PA Stages.................................................................................................. 21
9.3 Directional Coupler .................................................................................... 21
9.4 Antenna Switch.......................................................................................... 21
9.5 Harmonic Filter .......................................................................................... 22
9.6 Power Control ............................................................................................ 22
10.0 Frequency Synthesis............................................................................... 23
10.1 Reference Oscillator .................................................................................. 23
10.2 Fractional-N Synthesizer (U2701) ............................................................. 23
10.3 Voltage Controlled Oscillator (VCO) .......................................................... 24
10.4 Synthesizer Operation ............................................................................... 24
5C.3-ii
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Theory of Operation