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Chapter 4.1 VHF Detailed Theories of Operation
4.1.1 Introduction
This chapter provides a detailed circuit description of the ASTRO XTS 2500/XTS 2500
I
/XTS 2250/
XTS 1500 radio board. When reading the theory of operation, refer to the appropriate schematic and
component location diagrams located in the back of this manual. This detailed theory of operation
can help isolate the problem to a particular component.
This manual is to be used in conjunction with the ASTRO XTS 2500, XTS 2500
I
, XTS 2250,
XTS 1500, MT 1500 Digital Portable Radios Basic Service Manual (Motorola part number
6816984H01), which uses the pass/fail service approach to radio problems.
4.1.2 Frequency Synthesis
The complete synthesizer subsystem consists of the following:
• The
reference oscillator
(Y200)
• Two
voltage-controlled oscillators
(TX and RX)
• One
voltage-controlled oscillator buffer IC
(U250)
• The
synthesizer
(U202)
The
reference oscillator
contains a temperature-compensated 16.8 MHz crystal. This oscillator is
digitally tuned and contains a temperature-referenced, six-bit, analog-to-digital (A/D) converter. The
output of the oscillator (pin 3 on Y200) is applied to pin K9 (XTAL1) of U202 through capacitor C214.
The
voltage-controlled oscillators
(VCOs) are varactor-tuned. The voltage (2–9.5V) varies as it is
being applied to varactors D251 to D252 and D270 of their respective VCO. The capacitance of the
varactors also varies, thereby changing the output frequency of the VCOs. Both VCOs are used to
cover the entire 38 MHz bandwidth of the VHF range (136–174 MHz):
• TX VCO covers the transmit frequencies from 136–174 MHz
• RX VCO covers the receive frequencies from 180.85–218.85 MHz
The
TX and RX VCOs
are selected using AUX 3 from U202. Both VCOs are connected to the same
prescaler filter (C292, C266, L266 and R266) feeding back to PREIN of the U202, through C293.
The
synthesizer
IC consists of the following:
• A prescaler
• A programmable loop divider
• A divider logic control
• A phase detector
• A charge pump
• An A/D converter for low-frequency digital modulation
• A balance attenuator to balance the high-frequency analog modulation to the low-frequency
digital modulation
• A 13V positive voltage multiplier
• A serial interface for control
• A filter for the regulated 5 and 3 volts
Содержание ASTRO MT 1500
Страница 4: ...iv Table of Contents August 16 2007 6816985H01 B Notes ...
Страница 30: ...August 16 2007 6816985H01 B 2 1 4 VHF Overall Characteristics Vocoder Circuitry Overview Notes ...
Страница 34: ...August 16 2007 6816985H01 B 2 2 4 UHF1 Overall Characteristics Vocoder Circuitry Overview Notes ...
Страница 38: ...August 16 2007 6816985H01 B 2 3 4 UHF2 Overall Characteristics Vocoder Circuitry Overview Notes ...
Страница 42: ...August 16 2007 6816985H01 B 2 4 4 700 800 MHz Overall Characteristics Vocoder Circuitry Overview Notes ...
Страница 46: ...August 16 2007 6816985H01 B 2 5 4 900MHz Overall Characteristics Vocoder Circuitry Overview Notes ...
Страница 140: ...August 16 2007 6816985H01 B 4 4 20 700 800 MHz Detailed Theories of Operation VOCON Functional Blocks Notes ...
Страница 164: ...August 16 2007 6816985H01 B 5 6 Troubleshooting Procedures Operational Error Codes Notes ...
Страница 188: ...August 16 2007 6816985H01 B 6 1 24 VHF Troubleshooting Charts Secure Hardware Failure Notes ...
Страница 212: ...August 16 2007 6816985H01 B 6 2 24 UHF1 Troubleshooting Charts Secure Hardware Failure Notes ...
Страница 236: ...August 16 2007 6816985H01 B 6 3 24 UHF2 Troubleshooting Charts Secure Hardware Failure Notes ...
Страница 260: ...August 16 2007 6816985H01 B 6 4 24 700 800 MHz Troubleshooting Charts Secure Hardware Failure Notes ...
Страница 284: ...August 16 2007 6816985H01 B 6 5 24 900 MHz Troubleshooting Charts Secure Hardware Failure Notes ...
Страница 296: ...August 16 2007 6816985H01 B 7 1 12 VHF Troubleshooting Waveforms PP7 TX LO 7 1 11PP7 TX LO Probe point TP299 ...
Страница 301: ...6816985H01 B August 16 2007 VHF Troubleshooting Waveforms TP13 Mod In 7 1 17 7 1 16TP13 Mod In Test point TP36 ...
Страница 324: ...August 16 2007 6816985H01 B 7 1 40 VHF Troubleshooting Waveforms PP33 SPI Data 7 1 39PP33 SPI Data Probe Point R802 ...
Страница 325: ...6816985H01 B August 16 2007 VHF Troubleshooting Waveforms PP34 SPI CLK 7 1 41 7 1 40PP34 SPI CLK Probe Point R803 ...
Страница 342: ...August 16 2007 6816985H01 B 7 2 12 UHF1 Troubleshooting Waveforms PP7 TX LO 7 2 11PP7 TX LO Probe point TP299 ...
Страница 347: ...6816985H01 B August 16 2007 UHF1 Troubleshooting Waveforms TP13 Mod In 7 2 17 7 2 16TP13 Mod In Test point TP36 ...
Страница 371: ...6816985H01 B August 16 2007 UHF1 Troubleshooting Waveforms PP33 SPI Data 7 2 41 7 2 39PP33 SPI Data Probe Point R802 ...
Страница 372: ...August 16 2007 6816985H01 B 7 2 42 UHF1 Troubleshooting Waveforms PP34 SPI CLK 7 2 40PP34 SPI CLK Probe Point R803 ...
Страница 378: ...August 16 2007 6816985H01 B 7 2 48 UHF1 Troubleshooting Waveforms TP39 RX SSI Frame Sync Notes ...
Страница 390: ...August 16 2007 6816985H01 B 7 3 12 UHF2 Troubleshooting Waveforms PP7 TX LO 7 3 11PP7 TX LO Probe point TP299 ...
Страница 395: ...6816985H01 B August 16 2007 UHF2 Troubleshooting Waveforms TP13 Mod In 7 3 17 7 3 16TP13 Mod In Test point TP36 ...
Страница 418: ...August 16 2007 6816985H01 B 7 3 40 UHF2 Troubleshooting Waveforms PP33 SPI Data 7 3 39PP33 SPI Data Probe Point R802 ...
Страница 419: ...6816985H01 B August 16 2007 UHF2 Troubleshooting Waveforms PP34 SPI CLK 7 3 41 7 3 40PP34 SPI CLK Probe Point R803 ...
Страница 486: ...August 16 2007 6816985H01 B 7 5 12 Troubleshooting Waveforms PP7 TX LO 7 5 11PP7 TX LO Probe point Shield Tx_INJ ...
Страница 492: ...August 16 2007 6816985H01 B 7 5 18 Troubleshooting Waveforms TP13 Mod In 7 5 17TP13 Mod In Test point TP203 ...
Страница 501: ...6816985H01 B August 16 2007 Troubleshooting Waveforms PP22 Analog 5V 7 5 27 7 5 26PP22 Analog 5V Probe point U500 pin 5 ...
Страница 517: ...6816985H01 B August 16 2007 Troubleshooting Waveforms PP33 SPI Data 7 5 43 7 5 42PP33 SPI Data Probe Point R802 ...
Страница 518: ...August 16 2007 6816985H01 B 7 5 44 Troubleshooting Waveforms PP34 SPI CLK 7 5 43PP34 SPI CLK Probe Point R803 ...
Страница 521: ...6816985H01 B August 16 2007 Troubleshooting Waveforms TP37 RX SSI Data 7 5 47 7 5 46TP37 RX SSI Data Test Point TP403 ...
Страница 522: ...August 16 2007 6816985H01 B 7 5 48 Troubleshooting Waveforms TP38 RX SSI Clock 7 5 47TP38 RX SSI Clock Test Point TP404 ...
Страница 710: ...9 2 40 UHF1 Schematics Board Overlays and Parts Lists August 16 2007 6816985H01 B Notes ...
Страница 806: ...9 5 32 900MHz Schematics Board Overlays and Parts Lists August 16 2007 6816985H01 B Notes ...
Страница 816: ...Index 4 August 16 2007 6816985H01 B Notes ...
Страница 817: ......