4.1 - 2 MTM700 Mobile Radio / Detailed Service Manual THEORY OF OPERATION (400 MHz)
Receiver Section
The receiver section includes the following main components:
• Antenna Switch
• AGC_0 Attenuator
• Front End Pre-selector Filter
• Low Noise Amplifier (LNA)
• AGC_1 Attenuator
• Second Pre-selector Filter
•Mixer
• IF Filter
• IF Amplifier
• AGC_2 Attenuator and Buffer
• IF Digitizing Subsystem
The Receiver Path implements an Automatic Gain Control (AGC), which is required to maintain
good receiver linearity over a wide range of incoming signal levels and prevents clipping of high
level signals.
The IF Digitizing Subsystem performs the following functions:
• Carries out amplification and down conversion of the signal into the second IF.
• Performs IF AGC.
• Converts the second IF analog signal into baseband digital I & Q format.
• Transmits the I & Q baseband data to the DSP for further processing.
• Synthesizes the second LO frequency.
• Synthesizes the Sigma-Delta clock.
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