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Shure UC1 Body-Pack UHF Transmitter
Circuit Description
MIC. /
INSTR.
REMOTE
MUTE
FROM
ON / OFF
BATT.
SWITCH
FET
BYPASS
PWR.
CONTROL
HOLD
CIRCUIT
AUDIO IN
Audio Section
Service Procedures
LIMITER CONTROL INPUT
MIC. /
INSTR.
+5v
+5V
REG.
TONE KEY
UNREG. PWR.
OFF / MUTE DETECT
PLL CONTROL
SYNTH.
RF POWER
VCO
Figure 2. UC1 Circuit Block Diagram
Domestic Models
The audio signal enters the audio board at J204, pin 1. The signal
then enters a switchable 20 dB pad made up of SW203, R203, R204,
C204, and C206. The back-to-back diodes, U206, are used to keep
the op-amp from snapping to the rail and reverse-phasing when the
maximum input voltage range is exceeded.
The signal is ac-coupled through C205 into a 40 dB (30 dB for
J frequencies) user-adjustable gain stage around amplifier U2. This
gain stage is externally accessible to the user. Due to its topology, it is
a unique stage because it is non-inverting and allows for a gain less than
unity. Resistors R205 and R207 set up a half-supply bias, and R206 sets
the ac input impedance.
The amplified audio signal then passes through a pre-emphasis
network before entering the compression stage. R221, R222, C215,
and C216 set up two corners for the pre-emphasis network. The pre-
emphasis network feeds the NE575 compander, U203, which utilizes
2
TONE KEY
LIMITER
CONTROL OUTPUT
BATTERY
MGMT.
CIRCUIT
& FUEL
GAUGE
TONE CONTROL
EEPROM
MCU
GROUP
CHANNEL
RF MUTE
Σ
AUDIO
OUT
CALL ID
(MEM)
RF MUTE
25A1043 (RI)
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