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Shure UC4 Diversity Receiver

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-POLE

FILTER

COMPANDER DE-EMPHASIS

TONE

CONTROL

OUTPUT

STAGE

XLR OUT

1/4” OUT

TO AUDIO LEVEL BAR DISPLAY

SQUELCH

NOISE A

NOISE B

MARCAD

DIVERSITY

CIRCUIT

TONE KEY

DETECTOR

MUTING

CIRCUIT

LOW BATTERY

DETECTOR

TTL

CIRCUIT

TTL OUT

The audio for each channel comes from the appropriate channel

detector output of the rf section. Each channel’s 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 channel’s analog switch, allowing the audio to pass

through.

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Shure UC Manuale di Servizio Pagina 3

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