Hytera RD988 - UHF1 (400-470 Mhz) Information; TX Circuit

Service Manual
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9.UHF1 (400-470MHz) Information
9.1 TX Circuit
The TX circuit consists of power amplifier (PA) circuit, power control circuit, diagnosis and detection
circuit and protection circuit. It is to amplify the RF signal from exciter module to 50W, which then will be
wer control circuit is used for keeping the RF power of antenna at a fixed
level. For the diagnosis and detection circuit, it detects the current TX power, antenna VSWR and
transmitter temperature, and sends the detection result to the repeater’s control unit for monitoring the
transmitter status. The role of protection circuit is to protect the power amplifier from being damaged due
to high temperature or VSWR.
output via the antenna.
The po
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Vset
V_Contr
Sample FWD
RFIN
DAC
Figure 9-1 Block Diagram of PA Board
9.1.1 PA Module
The PA circuit of transmitter is composed of a 3-s A unit: pre-driver stage (Q401), driver stage
(Q402) and final-stage (Q403 and Q404). Q401 and Q402 form the driver circuit, whose gain can be
adjusted via the APC circuit, ensuring a constant RF ower output of 50W.
9.1.2 Pre-driver Stage PA
This PA unit is a LDMOS power tube (Q401). It can amplify the 13dBm RF signals from exciter unit to
tage P
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