Shure UC2, Руководство по обслуживанию

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Shure UC2 Hand-Held UHF Transmitter
Characteristics 5 25A1044 (RI)
The
VCO
output is also coupled to the pre-driver and rf power
amplifier through a resistive network (R322, R324, R325) and a
coupling capacitor, C329.
The pre-driver stage, Q302, provides approximately 6 to 8 dB of
gain, which makes up for the pad. R326 and R327 provide base bias
for the transistor, while R328 sets its operating current.
L303 is an rf choke used to provide power to the stage, while L304,
C332, C333, C357, and C2 provide filtering/matching for the stage. The
collector of Q302 feeds into the power amplifier stage via coupling
capacitor C338 and a pi-matching network made up of C339, L305,
and C340.
The rf power amplifier, Q304, is a dual emitter
BJT
. This high-gain,
high-frequency low-noise device can p18 dBm out at its 1 dB
compression point. It is biased via base resistors R331 and R332. Its
operating current is controlled via emitter resistor R333.
L306 acts as a choke, and C349, C350, C355, and C356 provide a
good emitter bypass to ground. The amplifier output is matched to low-
pass filter U1, via L307. The low-pass filter output couples to the printed
circuit board (pcb) via C347 and L308.
The transmitter can d17 dBm (50 mW) maximum to the
antenna for domestic frequencies; JA and JB frequency transmitters can
d10 dBm maximum to the antenna. During transmitter power-up
and frequency selection, the rf power is muted by bringing the gates of
Q303/Q305 low. This provides approximately 45 dB rf attenuation until
the
PLL
has locked.
The transmitter rf is then unmuted by bringing the gates Q303/Q305
high. During transmitter power off conditions, voltage is first removed
from the
VCO
by bringing the base of Q301 high. Thus, the carrier signal
of the transmitter is not allowed to drift off frequency during power on/off
conditions.
Digital Section
The digital section contains several circuitry blocks.
Microcontroller Section
The microcontroller section consists of the U303 microcontroller.
The rotary switches indicate the UHF frequency group and channel. A
4.000 MHz oscillator provides the operating frequency to the microcon-
troller. The oscillator circuit includes C300, C301, and Y301. U5, R306,
and C305 form the reset circuit. U5 is the reset IC that resets the U303
microcontroller if the 5 Vdc normal operating voltage falls below 4.3 Vdc.
C302 and C303 form the power supply bypass filter circuit.