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Extracted text from shure uc 4 service manual (Ocr-read)
Page 1
1999, Shure Incorporated Printed in U.S.A.
25C1045 (TK)
Service Manual
UC4 Diversity UHF Receiver
25C1045 (TK)
Characteristics
General
The Shure UC4 Diversity UHF Receiver is a microprocessor-
controlled single diversity receiver operating in the 692 to 716 MHz and
774 to 862 MHz frequency range. The UC4 is used in mid-level installed
sound, rental, and concert sound applications.
Controls and Connectors
1. Diversity Indicators
2. Squelch Control
3. Rf Level Indicators
4. Audio Level Indicators
5. Low Transmitter Battery Indicator
6. Group Rotary Switch
7. LED Display
8. Channel Rotary Switch
9. Equalization (
EQ ) Adjustment Controls10. Level (Volume) Control
11. Power On/Off Switch
12. Power Input Connector
13. Balanced (
LOW Z ) Output Connector
14.
MIC/LINE Side Switch
15. Unbalanced (
HIGH Z ) Output Connector
16.
LOGIC OUT Connector
17. Antenna Input Connectors
Figure 1.UC4 Controls and Connectors
A B R
1
5 8 10 3 4 6
12
11 9
13 14 15 16 17
7 2
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 Incorporated.
Licensing: Operation may require a user license. Frequency or power-output modifica-
tions may violate this products approvals. Contact your countrys communications authori-
ties.
Page 2
Shure UC4 Diversity Receiver
2 Parts Designations 25C1045 (TK)
Circuit Description
The audio circuit and rf circuit description will describe only one
channel because the other channel is identical for both. The local
oscillator (LO) section is common for both channels and will be
described separately.
Audio Section
Figure 2.UC4 Audio Section Block Diagram
AUDIO A
AUDIO B 4-POLELPFILTERCOMPANDER DE-EMPHASISTONE
CONTROLOUTPUT
STAGE
XLR OUT
1/4 OUT
TO AUDIO LEVEL BAR DISPLAY
SQUELCH NOISE A
NOISE B MARCADDIVERSITY
CIRCUITTONE KEY
DETECTORMUTING
CIRCUIT
LOW BATTERY
DETECTOR
TTLCIRCUIT TTL OUT
The audio for each channel comes from the appropriate channel
detector output of the rf section. Each channels audio then enters its
own adjustable gain stage.
This adjustable gain stage is used to match the audio levels coming
from each rf channel, as well as to set the correct level necessary for the
compander.
From the gain stages, each channel enters an analog switch. Noise
outputs also come from each channel detector outputs. Each noise
output enters a bandpass noise filter that measures the 50 kHz noise
present in the audio signal. The noise level is proportional to the signal-
to-noise ratio of the channel.
In the
MARCAD diversity system, a rectified version of the noise is
sent to a bank of comparators. A version of the channel noise that is 6
dB less also enters the comparators.
The noise from one channel is compared to the noise from the other
to make sure they are within 6 dB of each other. If the noise levels are
within 6 dB of each other, the comparators send a logic high signal to the
control of each channels analog switch, allowing the audio to pass
through.