Shure orporated UC2B User Manual
Characteristics
General
The Shure UC2 Hand-Held UHF Transmitter is a microprocessorcontrolled microphone transmitter, operating in the 774 to 862 MHz
frequency range. The UC2 hand-held transmitter is used in mid-level
installed sound, rental, and concert sound applications. Six frequency
range variations are available.
Controls and Connectors
Service Manual
UC2 Hand-Held
UHF Transmitter
1
2
1. Mic Cartridge Grille (87 shown)
2. Battery Fuel Gauge LEDs
3. Power ON/OFF Switch
4. Audio Gain Control
Figure 1. UC2 Controls and Connectors
Service Note:
performed by a Factory-Authorized Service Center or that the
product be returned directly to Shure Brothers Inc.
3
48
5
7
6
5. 9 V Battery
6. Battery Cup
7. Group Selection Rotary Switch
8. Channel Selection Rotary Switch
Shure recommends that all service procedures be
E1998, Shure Brothers Inc. Printed in U.S.A.
25A1044 (RI)
Shure UC2 Hand-Held UHF Transmitter
Circuit Description
LIMITER
CONTROL INPUT
FROM
BATT.
CONTROL
MIC
ON / OFF
SWITCH
FET
BYPASS
PWR.
HOLD
CIRCUIT
AUDIO IN
+5V
REG.
UNREG. PWR.
PWR. OFF DETECT
SYNTH.
MB15A02
RF POWER
+5v
32.768 kHz
PLL CONTROL
4 MHz
LIMITER
CONTROL OUTPUT
TONE KEY
CIRCUIT
TONE CONTROL
BATTERY
MGMT.
& FUEL
GAUGE
MCU
MC68HC705
GROUP CHANNEL
RF MUTE RF MUTE
TONE KEY
CALL ID
4 MHz
EEPROM
(MEM)
Σ
AUDIO
OUT
Audio Section
VCO
Figure 2. UC2 Hand-Held Transmitter Circuit Block Diagram
FCC-Approved
Audio enters L200, an inductor used as an rf choke. The signal is
ac coupled through capacitor C200 into a user adjustable gain stage.
Resistors R202 and R203 set up a half-supply bias, and R204 sets the
input impedance for the stage.
The back-to-back diodes, D201, are used to keep the op-amp from
snapping to the rail and reverse phasing when the maximum input voltage range is exceeded.
The 30 dB adjustable gain stage is built around U200A. The user
externally controls the gain of this stage. C206, C207, and C208 protect
Characteristics
2
25A1044 (RI)
Shure UC2 Hand-Held UHF Transmitter
the amplifier and bias circuits from rf interference. Due to its topology,
this stage is unique because it is non-inverting and allows for a gain less
than unity.
Audio then enters a buffer to the pre-emphasis network and the
compression stage. R213, R214, and C211 set up two corners for the
pre-emphasis network. The pre-emphasis boosts the high frequencies
before transmission.
This network feeds an NE575 compander, U202, that utilizes an
external amplifier, U201B. The compander performs a 2:1 logarithmic
compression of the audio signal. The pre-emphasis network also plays
a role in setting the hinge point (0 dB gain) of the compander.
From the compressor, the processed audio enters a low-pass filter,
U201D, and then a summing amplifier, U201C. The tone key (and for
J frequencies, the call ID signal) is added here to the processed audio
signal.
Transistors Q208 and Q209, with crystal Y200, form the tone key
oscillator circuit to provide a stable, continuous 32.768 kHz sine wave.
Transistor Q210 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 output
only when the tone key signal is present with the transmitted signal. If
the tone key or the transmitter is turned off, the receiver will be muted.
The tone key squelch eliminates receiver noise associated with
loss of a carrier. Q211 acts as a switch for toggling the tone key
UNMUTE
fed to a summing amplifier, U201C. R244, at the output of the summing
amplifier, helps prevent spurious oscillations from the op-amp. After
passing the ac coupling capacitor, C243, the signal is fed to the rf module
via the rf choke, L207.
D205; and various resistors. The meter works by comparing a divided
down version of the battery voltage (R250, R251) to two thresholds
(set by R252, R253, and R254), and lighting the appropriate LED.
(pcb), via switch S200. FET Q203 provides electrical reverse battery
protection by connecting the negative battery terminal to the pcb ground
only when the battery is connected with the correct polarity.
gives a clean, regulated 5 V supply to run the audio circuitry. The
regulator has appropriate bypass capacitors on its input and output.
Q201, Q202, Q212, Q213, and their respective resistors, provide
power management and timing.
; it is controlled via the microprocessor.
The tone key signal, along with the processed audio signal, is then
The battery meter circuit is comprised of U205; LEDs D203, D204,
A 9 Vdc battery provides power to the audio printed circuit board
The 9 Vdc then enters U203, a low dropout 5 V regulator, which
MUTE/
325A1044 (RI)
Characteristics
Shure UC2 Hand-Held UHF Transmitter
ETSI-Approved
This transmitter uses the same pcb as the domestic system, but 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 the NE575 (U202) is now activated and used as a
limiter. A sample of the audio is taken from the limiter output, U202,
pin 6, and sent to a control circuit that detects signals above a limiting
threshold. The comparator then sends a control signal to U202, pin 5,
which clamps the signal.
Rf Section
Processed audio enters R320, an internal potentiometer that is
adjusted for 45 kHz deviation (40 kHz for England), 100% modulation,
with a 6.8 dBu 1 kHz tone at the output of the compressor. For J frequencies, R320 is adjusted for 5 kHz deviation with 1 kHz tone injected
into the mic input, to give –23.47 dBu at U201, pin 7 (TPA4).
The audio is then fed to the tuning voltage pin of the voltage controlled oscillator (
locked-loop (
multiplier stages and results in a much higher degree of spectral purity.
The VCO is shielded to prevent external rf fields from affecting its
operation. Regulated 5 Vdc power from the low drop-out regulator,
U311, is provided to ensure frequency stability with changes in battery
voltage.
VCO is capable of tuning from 782 to 806 MHz (FCC-approved),
The
with a 1 to 4 V tuning voltage range. At the output of the VCO, the rf
signal splits into two paths. Frequency variations by country are given
in a table in the
The output of the
pin of the synthesizer, U304. The synthesizer’s internal circuitry divides
the rf signal down, as necessary. The synthesizer contains a quartz-controlled reference oscillator circuit operating from a 4.0 MHz crystal, Y302,
that is adjusted by trimmer C314.
The transmitter output frequency is user-selectable in groups of
compatible channels from 782 to 806 MHz for domestic groups. Frequency selection is made via microprocessor U303, which interfaces with
the user by means of the Group/Channel switches, S301 and S302.
VCO), which modulates the carrier directly . A phase
PLL) frequency-synthesized system eliminates the need for
Service Procedures
VCO is coupled by C323 to the frequency control
section.
Characteristics
The output of the synthesizer is a series of pulses integrated by a
passive loop filter (R316, C319, R317, C353, R318, C320) to produce a
control voltage signal. The control voltage signal is then connected to
VCO through buffer amplifier U306B, which is used to isolate the PLL
the
filter from the audio modulation signals.
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25A1044 (RI)
Shure UC2 Hand-Held UHF Transmitter
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
high-frequency low-noise device can provide +18 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 lowpass filter U1, via L307. The low-pass filter output couples to the printed
circuit board (pcb) via C347 and L308.
The transmitter can deliver +17 dBm (50 mW) maximum to the
antenna for domestic frequencies; JA and JB frequency transmitters can
deliver +10 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
PLL has locked.
the
The transmitter rf is then unmuted by bringing the gates Q303/Q305
high. During transmitter power off conditions, voltage is first removed
from the
of the transmitter is not allowed to drift off frequency during power on/off
conditions.
VCO by bringing the base of Q301 high. Thus, the carrier signal
BJT. This high-gain,
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 microcontroller. 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.
525A1044 (RI)
Characteristics
Shure UC2 Hand-Held UHF Transmitter
Memory Section
The memory section consists of U302, a non-volatile, Electrically
Erasable/Programmable Read Only Memory (
mapping of the compatible groups and channels. The microcontroller
serially communicates with this part via data and clock lines to read the
frequency corresponding to the Group and Channel position.
The ability to write to the memory occurs during factory programming
only. During normal usage, this memory is used as a look-up table only.
R335 and R305 resistors allow the clock and data lines to be driven
independently of the microcontroller port pin states during in-circuit programming of the
EEPROM.
Battery Management Section
The U303 microcontroller provides low battery shutdown. The shutdown threshold is 1.88 Vdc ± 10%. A voltage lower than the shutdown
threshold on U303, pin 17, shuts down the transmitter. Resistors R308
and R309 divide down the battery voltage for U303; a battery voltage
less than 5.65 Vdc must shut down the transmitter.
EEPROM) that stores the
This auto shutdown disables the audio tone key mix, mutes the rf
output, and powers down the rf output amplifier section. The current
draw from a 9 Vdc battery in this state is 14 ± 2.0 mA, and the battery
fuel gauge is not functional. Turning off the power switch completely
shuts off the transmitter.
The audio circuit description section provides information for the
battery fuel gauge circuit description.
Rotary Switches for Frequency Selection
A 10-position Group switch (S302) and a 16-position Channel switch
(S301) select the transmitter frequency. Both rotary switches share the
same U303 microcontroller port pins (3 through 6) for a multiplexed
switch read operation. The individual switches are selected by U303,
pins 7 and 8. Resistors R4, R300, R302, and R303 are the pull-ups for
the switch position read. Diode packs D301 through D304 isolate the
switches during the multiplexed read operation.
The multiplexed scheme to read switches does not allow incorporating switch change detection based on interrupts. Also, the switches cannot be constantly scanned to determine changes because the scanning
frequency being in audio range is difficult to filter out.
In a steady state, the switch selector common pins are inputs to the
U303, pins 7 and 8, while U303, pins 3 through 6, are outputs. In this
state, pins 4, 5, and 6 are held low while pin 3 is held high. This forces
logic high level on switch selector pins if the switches are set on odd
positions. For even position settings, the contact on pin 1 is open from
the switch common pin and the internal pull-down resistors force logic
low to U303, pins 7 and 8.
Characteristics
6
25A1044 (RI)
Shure UC2 Hand-Held UHF Transmitter
Any switch change is comprised of state toggle from odd to even,
and vice versa. Only this change is detected, and it is followed by a
multiplexed switch read, in which U303, pins 7 and 8, become selectively
grounded outputs to read the selected switch’s state on pins 3 through 6.
A multiplexed switch read is preceded by tone key and rf mutes.
This mutes the audio in the receiver to allow a quiet change to another
frequency.
For JA frequencies, the Group switch has 16 positions, and the
Channel switch has 10 positions.
Power Switch and Mute Interface
When a transmitter is turned off, the PWRDN signal goes to logic low
on U303, pin 19. This immediately disables the tone key, and the power
hold circuit automatically kicks in to bypass the power switch. This is
followed by 500 mS of delay, and then the rf is muted and turned off.
The power hold circuit is also disabled at this point, and the transmitter
shuts off.
725A1044 (RI)
Characteristics
Shure UC2 Hand-Held UHF Transmitter
Notes
Notes
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8
25A1044 (RI)
Shure UC2 Hand-Held UHF Transmitter
Functional Test
Verify operation and reported malfunction, referring to the product
User’s Guide for a description of the unit as well as information on its
operation, troubleshooting, and technical data.
Disassembly and Assembly
! CAUTION !
Observe precautions when handling this static-sensitive device.
Disassembly
Handle
1. Remove the microphone cartridge from the UC2.
2. Use a pair of needlenosed pliers to remove the circuit board
retaining ring from inside the handle.
3. Push the bezel tab-snap in the handle behind the contact pcb to
remove the bezel and switch actuator.
4. Slide the circuit board out by pushing on the battery connectors.
Bezel
Switch actuator
Tab
Tab
Right side view of microphone
Contact pcb
Circuit board subassembly
Figure 3. Bezel Removal
925A1044 (RI)
Functional Test
Shure UC2 Hand-Held UHF Transmitter
ÁÁÁ
Ball screen
Retaining
ring
Rf circuit
board
Microphone
cartridge
Contact
board
(SM58 shown)
Audio circuit
board
Gain control
Handle
Gain control
access
Bezel
Switch
actuator
9 Vdc a lkali ne
battery
Battery cup
Figure 4. UC2 Hand-Held Transmitter , exploded view.
Reassembly
To reassemble the unit, reverse the disassembly steps given above:
1. Slide the circuit board back into the handle.
2. Reinstall the retaining ring, switch actuator, bezel, and the
Disassembly and Assembly
microphone cartridge.
10
25A1044 (RI)
Service Procedures
Measurement Reference
dBu is a measure of
For example, the HP8903 should be labeled dBu instead of dBm
because it is a voltage measurement. These two terms are often used
interchangeably even though they have different meanings.
Audio levels in dBu are marked as dBm on the HP8903.
0 dBV = 2.2 dBu
0 dBu = 0 dBm, assuming the load = 600 Ω
Test Equipment
Most test equipment needed is described in the Shure
Service Equipment Manual
equivalent) is also needed.
Shure UC2 Hand-Held UHF Transmitter
voltage
dB Conversion Chart
, and dBm is a measure of
. The following test equipment (or approved
Table 1
power
Wireless
Test Equipment
.
Equipment T ype Model
Digital multimeter Fluke 87
Rf signal generator Hewlett-Packard 8656B
Frequency counter Hewlett-Packard 53181A
Spectrum analyzer (domestic) Hewlett-Packard 8590L
Spectrum analyzer (JA, JB) Hewlett-Packard 8591E
Shure UC4 receiver Shure UC4
Brass ring for use with test head PT1838–Y
BNC to “rocket launch” cable 95C8418–1
*Audio levels in dBu are marked as dBm on the HP8903B.
Test Equipment Set-Up
The alignment procedure is sequential and does not change,
unless specified.
1. Use RG58 or any low loss, 50 Ω cables for all rf connections.
Use a BNC to “rocket launch” cable for J frequencies.
2. Keep the test cables as short as possible.
Audio analyzer *Hewlett-Packard 8903B
Test head PT1840
3. Include the insertion loss of the cables and connectors for all rf
measurements.
4. Dc voltages may be present at rf test points. As a precaution,
use dc blocks to protect the test equipment
1125A1044 (RI)
Service Procedures
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