5
Basic Theory of Operation
3
General
Overview
The ASTRO Digital XTS 2500 / XTS 2250 / XTS 1500 radio and the MT 1500 / PR
1500 radio are wideband, synthesized, fixed-tuned radios available in the VHF
band. The XTS 2500 / XTS 2250 / XTS 1500 radios are capable of both analog
operation (12.5 kHz or 25 kHz bandwidths) and digital ASTRO mode operation
(12.5 kHz only). The MT 1500 and PR 1500 radios operate in analog only.
For the secure models only, the encryption module is designed to digitally encrypt
voice for ASTRO and Non-ASTRO radios. The secure models are available in XTS
2500 models 1.5, II and III and XTS 2250 models 1.5 and III.
NOTE: The encryption modules are NOT serviceable.
The XTS 2500/2250/1500 radios include the following major assemblies (see
Figure 1):
• Main Board: contains the microcontrol unit (MCU) and its associated memory
and memory management integrated circuit (IC), the audio power amplifier,
and a switching regulator. The board also contains the digital signal processor
(DSP) and its support IC and associated memories. It further contains all
transmit, receive, and frequency generation circuitry, including the digital
receiver back-end IC and the reference oscillator.
• Universal Flex: contains the universal connector, speaker, and microphone.
• Display (XTS 2500 Models 1.5, II and III and XTS 2250 1.5 and Advanced
Model only): a six-line, 12-character, liquid-crystal display (LCD).
• Keypad (XTS 2500 Models II and III and XTS 2250 Advanced Model only):
- XTS 2500 Model II: a 3 x 2 keypad
- XTS 2500 Model III and XTS 2250 Advanced Model: a 3 x 6 keypad.
• Keypad with secure option (XTS 2500 Models 1.5, II and III and XTS 2250
Models 1.5 and III Secure Models only):
- XTS 2500 and XTS 2250 Model 1.5: no keypad with secure option
- XTS 2500 model II: 3 x 2 keypad with secure option
- XTS 2500 and XTS 2250 model III: 3 x 6 keypad with secure option
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