QUANTUN QP-650 Plus, Руководство по обслуживанию

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QP-650 Plus Circuit Description
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Fig. 4 APC System
Antenna switch and LPF
Output signal from RF amplifier passes through a low-pass filter network and a transmit/receive
switch circuit comprised of D401
，
D501 and D502 before it reaches the antenna terminal. D501 and
D502 is turned on (conductive) in transmit mode and off (isolated) in receive mode.
APC
The automatic power control (APC) circuit stabilizes the transmit output power by detecting the
drain current of final stage amplifier FET. U430 (2/2) compares the preset reference voltage with the
voltage obtained from final current. APC voltage is proportional to the difference between auto detect
voltage and reference voltage output from U430
（
1/2
）
. The output voltage controls FET power.
5. Base band and signaling system
The block diagram of signaling section is shown as figure 5.