Shure UC1L Service Manual page 3

Rf Section
25A1043 (RI)
an external amplifier, U202B. U203 performs a 2:1 logarithmic compres-
sion of the audio signal.
Transistors Q201 and Q202, with crystal Y201, form the tone key
oscillator circuit that provides a stable, continuous 32.768 kHz sine
wave. Q204 buffers the tone key signal before it is added to the audio
signal. The tone key signal is used in the receiver to provide audio out-
put only when the tone key signal is present in the transmitted signal.
If the tone key or the transmitter is turned off, the receiver is muted.
Q211 acts as a switch for toggling the tone key
trolled from the microprocessor, via the
key signal, along with the processed audio signal, is then fed to a sum-
ming amplifier, U201A. After passing through the ac coupling capacitor,
C240, the signal is then fed to the rf module.
The battery meter circuit is comprised of comparator U208 and
s D201, D202, D203, and various resistors. When the battery circuit
LED
is less than 6.5 Vdc, the output of U208, pin 13, changes low, the red
illuminates, and the tone-key level increases. The receiver then
LED
utilizes the amplitude of the tone-key to indicate that the transmitter
battery is low.
A 9 Vdc battery provides power to the audio printed circuit board
(pcb) through switch SW202.
battery protection. 9 Vdc enters U205, a low-dropout 5 Vdc regulator,
and gives a clean regulated 5 Vdc supply to run the audio circuitry.
ETSI Models
This transmitter uses the same board as the non-ETSI system,
except that it requires a different topology and different parts.
A limiter is inserted between the pre-emphasis and the compressor
to limit the occupied bandwidth. The buffer after the gain stage, U201A,
is now an inverter with pre-emphasis and 20 dB of attenuation.
Previously bypassed, the expander side of U203 is now activated
and used as a limiter. A sample of the audio is taken from the limiter
output (U203, pin 6) and sent to a control circuit which detects signals
from a limiting threshold.
The comparator then sends a control signal to U202, pin 5, which
clamps the signal.
Processed audio enters R149, an internal potentiometer that is
adjusted for 45 kHz deviation (100% modulation for UA, MA, and MB
frequencies), with a –7.2 dBV (0.355 Vrms) 1 kHz tone at the output
of the front audio stage (U201, pin 1). For KK frequencies, R243 is
adjusted for 40 kHz deviation. For JB frequencies, R149 is adjusted for
5 kHz deviation with –63.2 dBV, 1 kHz tone at the input to the transmitter.
3
Shure UC1 Body-Pack UHF Transmitter
TONEMUTE0
Q217 provides electrical reverse
FET
. It is con-
ON/OFF
signal. The tone
Characteristics