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Shure UC4 Diversity Receiver

Parts Designations

25C1045 (TK)

Rf Section

Figure 3. UC4 Rf Section Block Diagram

DIELECTRIC

FILTER

DIELECTRIC

FILTER

LNA

FIRST

MIXER

SECOND

MIXER

FIRST IF

FILTER

SECOND IF

FILTER

DETECTOR

AUDIO A

NOISE A

RSSI A

RF CHANNEL A

DIELECTRIC

FILTER

DIELECTRIC

FILTER

LNA

FIRST

MIXER

SECOND

MIXER

FIRST IF

FILTER

SECOND IF

FILTER

DETECTOR

AUDIO B

NOISE B

RSSI B

RF CHANNEL B

FROM

MICROPROCESSOR

SYNTHESIZER

VCO

LOW PASS

FILTER

FIRST LO

SECOND LO

The rf input signal is provided from the antenna ports to the receiver

by BNC connectors. Antenna port A is connected to J101 (channel A),

and antenna port B is connected to J201 (channel B).

The rf circuit description will describe only one channel because the

other rf channel is identical. The local oscillator (LO) section is common

for both channels and will be described separately.

Rf Channel

The rf signal is pre-selected to the 782 – 806 MHz frequency range

with two dielectric filters. The first dielectric filter is located between the

antenna port and the low noise amplifier (

LNA). The second filter is

located between the

LNA block and mixer input.

The

LNA and the first mixer consist of a dual gate GaAs MOSFET.

The first conversion gives the first intermediate frequency (IF) signal at

50 MHz.

The first IF signal is amplified with

MMIC, band limited with a SAW

filter, and then down-converted to the second intermediate frequency (IF)

at 10.7 MHz with a second down-converter.

The second

IF signal is filtered by 10.7 MHz ceramic filters and

amplified by a 10.7 MHz pre-amp (Q105).

The 10.7 MHz signal goes to the second IF gain block with a

detector. The audio output is buffered and then processed as stated in

the audio section circuit description. The noise output is amplified to pro-

vide signal for the noise squelch circuitry. The Received Signal Strength

Indication (RSSI) output of the detector drives the LEDs that are located

on the receiver’s front panel.

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