TRANSCEIVER 800 MHz
MTP700 Portable Radio / Detailed Service Manual
4.2 - 3
Receiver Section
The receiver section includes the following main components:
•
Antenna Switch
•
Limiter
•
Front Filter (First Pre-selector)
•
Low Noise Amplifier (LNA)
•
Second Pre-selector
•
Mixer
•
IF Filter
•
Balun
•
WPIC
The Receiver Path implements an Automatic Gain Control (AGC). It is required to main-
tain good receiver linearity over a wide range of incoming signals and prevents clipping of
high level signals.
The First Intermediate frequency (IF) circuit consists of the Mixer, IF Filter, and WPIC.
The First IF is down converted to baseband using an analog mixer (high-side injection)
located in the WPIC. An external second LO synthesizer IC is used to generate the
required 219.3 MHz signal, which is further divided by two to 109.65 MHz before being
applied to the mixer.
The WPIC performs the following functions:
•
Carries out amplification and quadrature down conversion of the signal into base-
band.
•
Synthesizes the second VCO frequency.
•
Performs IF AGC.
•
Converts the baseband analog signal into digital I & Q formats.
•
Synthesizes the receive and transmit data (ie Sigma-Delta) clock.
•
Transmits the received data to the DSP.
Transmitter Section
The transmitter circuitry includes a linear class AB Power Amplifier (PA) for the linear
modulation of the MTP700. It also includes a cartesian feedback loop to enhance its
transmitter linearity and reduced splattering power into adjacent channels.
The transmitter path consists of a forward path and a cartesian feedback loop. The for-
ward path includes the LNODCT (Low Noise Offset Direct Conversion Transmitter) ASIC,
Balun, Attenuator, and Power Amplifier. The loop feedback path includes the directional
coupler, attenuator and LNODCT.
The linearized power from the PA goes through the isolator which provides the isolation
between the antenna and the PA. The signal then passes through the antenna switch and
a lowpass Harmonic Filter to provide additional filtering to remove far out unwanted sig-
nals.
Содержание IMPRES Tetra MTP700
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