Vertex Standard VXR-7000 Service Manual page 27

APC (Automatic Power Control)
RF power output from the final amplifier Q1507 is
sampled by C1550/C1559 and is then rectified by D1503/
D1504 (both 1SS319). The resulting DC voltage is ap-
plied to the comparator Q1509 (TA75S01F), where the
voltage is compared with a reference voltage from the Main
CPU Q4012 on the CNTL Unit, to produce a control volt-
age for the Automatic Power Controller Q1503
(2SB1122S) and Q1504 (2SC4116GR), which regu-
lates supply voltage to the RF power module IC Q1502,
so as to maintain stable high (or low) output power under
varying antenna loading conditions.
C (CNTL) Unit
The CNTL Unit consists of 8-bit CPU Q4012
(HD64F3337YF16), EEPROM Q4008 (NM93C86A),
RX and TX speech audio circuits, and various analog
switches for the CPU and repeater interconnections.
Microprocessor operational code is stored in Q4008,
while channel data and repeater configuration informa-
tion is programmed from an external PC connected to the
front panel's MIC jack via a VPL-1 programming cable.
The output from the Main CPU Q4012, contains serial
control data used for REPEATER/BASE mode control,
as well as TX and RX PLL data. Crystal X4001 oscillates
at 16 MHz, and provides stable clock timing for the Main
CPU. When the repeater is powered on, the voltage at pin
8 of Q4012 becomes stable, and the output of voltage de-
tector IC Q4005 (RH5VL45AA), which is tied to Q4012
(pin 1-RST) becomes high, resetting the Main CPU.
Circuit Description
Base Operation (Tx, Line-Input Audio)
Line input from J4009 (pins 3 and 4) is impedance
matched by transformer T4001, then passes through the
audio amplifier Q4018-2 (NJM2902) and audio switch
Q4030 (NJU4066B) to the pre-emphasis network at
Q4018-1, where the signal is processed in the same man-
ner as previously described. The line level can be attenu-
ated by switch S4002, and line sensitivity can be adjusted
to –10 dBm by potentiometer VR4003 to compensate for
audio line level variations.
Base Operation (Tx, Mic-Input Audio)
Microphone input is delivered past the MIC MUTE
switch Q4026 (DTC323TK), then passes through the au-
dio amplifier and active high pass filter at Q4021-2/-3/-4
(NJM2902) to the pre-emphasis network at Q4018-1,
where the signal is processed in the same manner as pre-
viously described.
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