Motorola ASTRO Digital Spectra Plus - 2.5 Power Amplifier; 2.6 Front-End Receiver Assembly; 2.7 RF Board Basic; 2.8 Voltage-Controlled Oscillator

viii Table of Contents
September 5, 2008 6881076C25-E
3.5.1.5 RX Buffer Circuitry..................................................................................................3-48
3.5.1.6 Frequency Divider and TX Buffer Circuitry.............................................................3-48
3.5.2 UHF Band........................................................................................................................3-49
3.5.2.1 General...................................................................................................................3-49
3.5.2.2 Super Filter 8.6 V ...................................................................................................3-49
3.5.2.3 VCO........................................................................................................................3-49
3.5.2.4 Receive Mode (AUX2* Low)...................................................................................3-49
3.5.2.5 Transmit Mode (AUX2* High).................................................................................3-49
3.5.2.6 Bandshift Circuit .....................................................................................................3-49
3.5.2.7 Output Buffer ..........................................................................................................3-49
3.5.2.8 First Buffer..............................................................................................................3-49
3.5.2.9 Doubler...................................................................................................................3-50
3.5.2.10 Synthesizer Feedback............................................................................................3-50
3.5.2.11 Second Buffer.........................................................................................................3-50
3.5.2.12 Receive/Transmit Switch........................................................................................3-50
3.5.3 800 MHz Band.................................................................................................................3-50
3.5.3.1 General...................................................................................................................3-50
3.5.3.2 Super Filter 8.6 V ...................................................................................................3-50
3.5.3.3 VCO........................................................................................................................3-50
3.5.3.4 Receive Mode-AUX 1* and AUX 2* High ...............................................................3-51
3.5.3.5 Transmit Mode-AUX 1* High; AUX 2* Low.............................................................3-51
3.5.3.6 TalkAround Mode-AUX 1* Low; AUX 2* Low.........................................................3-51
3.5.3.7 VCO Buffer .............................................................................................................3-51
3.5.3.8 First Buffer Circuit...................................................................................................3-51
3.5.3.9 Doubler...................................................................................................................3-51
3.5.3.10 Second Buffer.........................................................................................................3-52
3.5.3.11 K9.4 V Switch .........................................................................................................3-52
3.6 Receiver Front-End ......................................................................................................................3-53
3.6.1 VHF Band........................................................................................................................3-53
3.6.1.1 General...................................................................................................................3-53
3.6.1.2 Theory of Operation ...............................................................................................3-53
3.6.2 UHF Band........................................................................................................................3-53
3.6.2.1 General...................................................................................................................3-53
3.6.2.2 Theory of Operation ...............................................................................................3-54
3.6.3 800 MHz Band.................................................................................................................3-54
3.6.3.1 General...................................................................................................................3-54
3.6.3.2 Theory of Operation ...............................................................................................3-54
3.7 Power Amplifiers ..........................................................................................................................3-55
3.7.1 VHF Band Power Amplifiers............................................................................................3-55
3.7.1.1 High-Power Amplifier..............................................................................................3-55
3.7.1.1.1 Transmitter ......................................................................................................3-55
3.7.1.1.2 Antenna Switch and Harmonic Filter...............................................................3-56
3.7.1.1.3 Power Control Circuitry ...................................................................................3-57
3.7.1.2 25/10-Watt Power Amplifier....................................................................................3-59
3.7.1.2.1 Antenna Switch and Harmonic Filter...............................................................3-60
3.7.1.2.2 Power Control Circuitry ...................................................................................3-60
3.7.1.3 50-Watt Power Amplifiers.......................................................................................3-63
3.7.1.3.1 Transmitter ......................................................................................................3-63
3.7.1.3.2 Antenna Switch and Harmonic Filter...............................................................3-64
3.7.1.3.3 Power Control Circuitry ...................................................................................3-65
3.7.2 UHF Band Power Amplifiers............................................................................................3-68
3.7.2.1 High-Power Amplifier..............................................................................................3-68
3.7.2.1.1 Transmitter ......................................................................................................3-68
3.7.2.1.2 Antenna Switch and Harmonic Filter...............................................................3-69