Shure_U1,U1L_Wireless_Transmitter_Service_Manual.pdf

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Shure Incorporated
222 Hartrey Avenue
Evanston IL 60202-3696 U.S.A.
UHF Wireless System
SERVICE MANUAL CHANGE NOTICE
U1/U1L UHF BODY-PACK TRANSMITTER
Changes and corrections have been made to the Service Manual for the U1/U1L UHF Body-Pack Trans-
mitter. These changes will make it easier to repair the transmitters. To update your Service Manual,
remove the pages identified in the tables below and replace them with the pages attached to this Change
Notice. Note that there are no changes to pages not specifically identified in the tables below.
U1/U1L SERVICE MANUAL REVISION HISTORY
Release
Original
Revision 1
Revision 2
Revision 3
Revision 4
Revision 5
Part Number
25A1021
25B1021
25C1021
25C1021
25C1021
25C1021
Date Code
QE
SA
TD
AG
BF
BG
CHANGES EFFECTIVE JULY 12, 2002
REMOVE
these pages from the
U1/U1L Service Manual
INSERT
these Revised pages into the
U1/U1L Service Manual
21 to 25
21 to 25
E
2000, Shure Incorporated
25–1021–2 (BG)
Printed in U.S.A.
Service Manual
U1/U1L Body-Pack
UHF Transmitter
General
Characteristics
The Shure U1/U1L Body-Pack UHF Transmitter is a microprocessor-
controlled body-pack transmitter operating in the UHF frequency range.
This product is intended for use in high-end installed sound, rental, and
concert sound applications. Different frequency variations are available.
Controls and Indicators
1
3
2
8
4
5
1
NOTE:
All models shipped after February 1999
have a soldered attached antenna to replace the
screw-on removable antenna. .
7
O O
N FF
9
6
10
11
12
13
1. Antenna
2. Programmable Display
3. Input Connector
(U1L uses LEMO connectors)
4. ON/OFF Switch
5. On/Off LED
6. Belt Clip
7. MODE Button
8.
9.
10.
11.
12.
13.
SET Button
Audio Gain Control
Battery Cover Release Tabs
Battery Compartment Cover
Battery Fuel Gauge
Battery Compartment
Figure 1.
U1/UL Transmitter Controls and Indicators
Service Note:
Shure recommends that all service procedures be performed by a Factory-Authorized
Service Center or that the product be returned directly to Shure Brothers Inc.
Licensing:
Operation may require a user license. Frequency or power-output modifications
may violate this product’s approvals. Contact your country’s communications authorities.
E
1999, Shure Incorporated
25B1021 (BG)
Printed in U.S.A.
Shure U1/U1L Body-Pack UHF Transmitter
Circuit Description
Audio Section
Audio enters L201, an inductor that is used as an rf choke. The
signal enters a 6 dB pad made up of R203, R204, C204, and C206.
The signal is ac-coupled through C205 into a 40 dB (30 dB for JB
frequencies) user-adjustable gain stage around U201A.
This gain stage is externally accessible to the user. C201, C202,
and C207 protect the pre-amplifier and bias circuits from rf interference.
R205 and R207 set up a half-supply bias, and R206 sets the ac input
impedance.
The amplified audio signal is then passed through a pre-emphasis
network before entering the compression stage. R208, R211, and C211
set up two corners for the pre-emphasis network. The pre-emphasis
network boosts the high frequencies before transmission and helps set
the hinge point (0 dB gain) of the compandor. The network feeds NE575
compandor U203, which utilizes an external amplifier U202B. The com-
pandor performs 2:1 logarithmic compression of the audio signal.
Transistors Q201 and Q202, along with crystal Y202, form the tone key
oscillator circuit, which provides a stable, continuous 32.768 kHz sine wave.
Transistor 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 output only
when the tone key signal is present in the transmitted signal. Therefore, if
the tone key or the transmitter is turned off, the receiver will be muted.
Q203 acts as a switch for toggling the tone key on and off. It is controlled
via the microprocessor. R224 allows the tone key amplitude level to be set.
The tone key circuit is powered by U208B, which is a dc amplifier
that multiplies the 3 V battery voltage to 4.5 V (gain = 1.5). As the battery
voltage drops, the tone key supply voltage also drops, which decreases
oscillator amplitude. The tone key amplitude is used by the receiver
to indicate transmitter battery strength.
The tone key feature indicates battery level at the receiver. It is not
available on JB models.
The tone key signal, along with the processed audio signal, is fed to
summing amplifier U202A. Resistors R232 and R233 set up a half-supply
bias. Resistor R231, located at the output of the summing amplifier, pre-
vents spurious oscillations from the operational amplifier. After passing
through ac-coupling capacitor C232, the signal is fed to the rf module.
Circuit Description
2
25C1021 (BG)
Shure U1/U1L Body-Pack UHF Transmitter
Rf Section
Processed audio enters R243, an internal potentiometer adjusted for
45 kHz deviation (100% modulation) with a –7.2 dBV, 1 kHz tone, at the
output of the front audio stage (pin 1 of U201). On JB models, R243 is
adjusted for 5 kHz deviation with –63.2 dBV, 1 kHz tone, at the input to
the transmitter.
The audio is then fed to the tuning voltage pin of the voltage controlled
oscillator (VCO) and modulates the carrier directly. The use of a phase
locked-loop (PLL) frequency synthesized system eliminates the need for
multiplier stages, resulting in a much higher degree of spectral purity. The
VCO is shielded against interference from external rf fields. Regulated
+5 Vdc power from the dc-to-dc converter ensures frequency stability,
even if the battery voltage changes.
At the output of VCO U205, the rf signal splits into two paths. The
output of the VCO is coupled by C244 to the frequency control pin of
synthesizer U204. The synthesizer’s internal circuitry divides the signal
as necessary to reach the desired reference frequency.
The synthesizer contains a quartz-controlled reference oscillator
circuit, including a 4.0 MHz crystal (Y201), that is adjusted by means of
trimmer capacitor C239.
The transmitter output frequency is user-selectable. Frequency
selection is made via microprocessor U103, which interfaces with the
user by means of the mode/select switches. The output of the synthesiz-
er is a series of pulses that are integrated by a passive loop filter (R238,
C245, R240, C266, C267, R239, and C247) to produce a control voltage
signal. The control voltage signal is then connected to the VCO through
amplifier U210A, which is used to isolate the PLL filter from the audio
modulation signals.
The VCO output is also coupled to an rf power amplifier through a
resistive pad consisting of R254, R255, R256, R257, and an LC match-
ing network containing C261, L209, and C248. The rf power amplifier,
dual gate MESFET Q208, is fixed-tuned and configured as a common
source device.
Amplifier stability is obtained through resistive loading on the input,
R247. The output of Q208 contains a low-pass matching network (L206)
and an LC-type low-pass filter (LP206), which provide a high degree of
spectral purity. The output of the low-pass filter feeds a microwave isola-
tor that reduces the production of reverse third-order intermodulation
products.
The transmitter is capable of delivering a maximum of +10 dBm
(10 mW) to the 50
Ω
antenna. During transmitter power-up and frequency
selection, rf power is muted by bringing the base of Q209 high. This pro-
vides approximately 45 dB rf attenuation until the PLL has locked. The
transmitter rf is then unmuted by bringing the base of Q209 low. During
transmitter power off conditions, voltage is first removed from the VCO by
bringing the base of Q207 high. In this way, the transmitter carrier signal is
not allowed to drift off frequency during power on or power off conditions.
25C1021 (BG)
3
Circuit Description

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