Manually Select a Group and/or Channel. Shure SLX 2

The SLX SLX2 is a frequency-agile UHF handheld transmitter. It operates for a minimum of 8 hours using two "AA" alkaline batteries. It is designed for use with SM58, BETA 58, SM86, and BETA 87A&C microphone heads, and features an internal antenna for optimum range and reliability. This product is intended for use in entry-level presentation, installed, and performance markets.

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Incompatible

MASTER LIST

GROUP CHANNEL

i8 i8 select b

Incompatible

MASTER LIST

GROUP

CHANNEL

i8 i8 select

SLX2 Transmitter Programming

Manually Select a Group and/or Channel

select

Press and hold the select button until the GROUP and CHANNEL displays begin to alternate.

To change the group setting, release the select button while GROUP is displayed a

. While GROUP is flashing, pressing select increases the group setting by one.

To change the channel setting, release the select button while CHANNEL is displayed b

. While

CHANNEL is flashing, pressing select increases the channel setting by one.

Incompatible

MASTER LIST

GROUP CHANNEL

i8 i8

Lock or Unlock Transmitter Settings

select

Press the mute/ and select buttons simultaneously to lock or unlock the transmitter settings. When locked, the current settings cannot be changed manually. Locking the transmitter does not disable in-

frared synchronization.

Incompatible

MASTER LIST

GROUP CHANNEL

i8 i8

Incompatible

MASTER LIST

GROUP CHANNEL

i8 i8

Battery Status

Indicates charge remaining in transmitter batteries.

Master List Indicator

Indicates that a master list frequency is currently in use. No group or channel information is displayed.

Note: the transmitter cannot be used to change master list settings.

Incompatible

MASTER LIST

GROUP CHANNEL

i8 i8

INCOMPATIBLE Frequency Warning

The INCOMPATIBLE warning indicates that the receiver and transmitter are transmitting on different frequency bands. Contact your Shure retailer for assistance.

25A1090 (Rev.3)

AUDIO/RF BLOCK DIAGRAM

User Gain

Control Switch

Preemphasis

VCA

2-pole,

17kHz,

LPF

Audio Input

(mic head)

EPROM

Limiter

LCD

Photodetector

32.768 kHz

LCD

Driver

Microcontroller

Tone Key

Frequency

Synthesizer control

Channel

Select,

Power Mute

Compressor

RF Muting

Audio Muting

Deviation Trim and Tone Key

Sum Amp

RMS

Detector

VCO (Carrier

Range)

LPF

AA Battery

Supply

Amp

Pad

0-4 dB (Band dependent)

DC-DC

Converter

+5V DC

Source

Amp

Pad

0-4 dB (Band dependent)

Loop

Filter

Frequency

Synthesizer

MHz

CIRCUIT DESCRIPTION

AUDIO CIRCUIT DESCRIPTION

AUDIO SECTION

Audio enters the transmitter board through pin 4 of the mic-jack board connector (CON100).

Pin 2 of the connector provides 5 Vdc bias for the mic head. Pin 6 supplies the ground connection. The audio preamp (IC150-2) provides either 0 or 10 dB of gain (user switchable via

SW100). Capacitor C140 couples the signal into a pre-emphasis network formed by R140, R141, and C141.

Next, the audio signal enters the patented Shure ARC™ processor. The main elements in this section are the VCA (IC100-5) and the RMS Detector (IC100-4). The VCA, or Voltage Controlled

Amplifier, is a DC controlled amplifier. Following the VCA, the signal enters a 3-pole 17kHz lowpass filter stage (IC100-2) that protects the RMS detector from energy above the audio band.

Next, the signal is coupled to the RMS detector (IC100-1), which converts it to a DC voltage. A

+1 dB increase at the input to the detector produces a +6 mV increase at its output. The detector output is fed to the compression threshold stage (IC150-2). This stage provides the transition from uncompressed to compressed signal. At low levels, the audio is uncompressed because diode D169 is turned off. As the AC level increases, the output of IC150-2 decreases enough to turn the diode on. As D190 conducts, the compression ratio changes from 1:1 to 5:1. Once D190 is turned fully on, the audio compression ratio remains fixed at 5:1. An additional diode in the bias

25A1090 (Rev.3)

network (D162) provides temperature compensation for changes in the V

, or "cut-in" voltage of

D190. After the compression threshold stage, the DC control signal is amplified by a 40 dB fixedgain stage (IC100-5). It is then sent to the VCA control voltage input (EC+).

Following the ARC™ processor section, the audio signal must pass through a muting network consisting of R199, R200, C205, and Q205. A trim pot (TR200) allows the audio deviation level to be set. Next, audio enters the tone key summing amp (IC150-4). Here, tone-key is added to the audio before passing to the RF section for transmission. The tone key signal is used in the receiver to provide audio output only when the tonekey signal is present with the transmitted signal; therefore, if the tone key or the transmitter is turned off, the receiver will be muted. The tone key squelch will eliminate receiver noise associated with loss of the carrier, which usually sounds like a "pop". The tone key signal is generated by a square wave from the mP (IC300). It is then filtered by active filter stage Q185 and attenuated by R188/R189 (under µP control) before being fed to the summing amplifier. The combined audio/tone-key signal is then sent to the VCO through R504.

POWER SECTION

Two "AA" batteries supply power to the transmitter through FET Q410, which provides electrical reverse battery protection. Next, power enters switching boost converter IC400, which supplies regulated 5V power. To turn on the transmitter, SW325 shorts the base of Q480 to ground, enabling the converter and powering up the unit. The microprocessor keeps Q480 disabled until shutdown.

Power is turned off by a "shutdown" signal from the microprocessor, which can be initiated manually by the user (by holding down SW325 for 2.2 seconds) or automatically by the system

(e.g., when the battery is too weak for proper operation). At this time, the microprocessor enables

Q480 and shuts down the converter. When the unit is off, Q480 and its bias circuitry draw less than 30 µA, so the effect on battery life is negligible. The converter and microprocessor are disabled.

LOW BATTERY SHUT DOWN:

A software battery shutdown routine allows the battery supply to run down to 2.05 V before shutdown, and will not turn the system back on until a voltage greater than 2.25 V is present. The hysteresis keeps the system in a controlled state when the batteries are low, and also helps prevent weak batteries from being used from the start.

RF CIRCUIT DESCRIPTION

RF SECTION

The system block diagram is shown above. The SLX2 uses a PLL system with direct carrier frequency modulation. Processed audio enters the VCO through a passive "reflection" network before being applied to the varactor diode (D500) through choke L503. The VCO is shielded to prevent external RF fields from affecting its operation, and to help control radiated emissions of its harmonics. Power for the VCO and PLL circuitry is supplied by the main 5 V regulator. Power and signal lines in the VCO area are heavily decoupled and bypassed to remove noise.

The VCO has a tuning bandwidth of more than 30 MHz on all bands, with a tuning voltage range of approximately 1 to 4 volts. The VCO employs separate stages for the oscillator (Q502) and buffer (Q501) to minimize phase noise and load pulling. The VCO output is isolated by capacitive and resistive dividers, before being applied to the frequency control pin of the PLL synthesizer (IC501) through C538. The synthesizer's internal circuitry divides the RF signal down as necessary to achieve a tuning precision of 25 kHz. The synthesizer circuit contains a quartz-controlled reference oscillator operating from a 16 MHz reference crystal (Y801) that is adjusted by means of trimmer CV501. The transmitter output frequency is user selectable in groups of compatible channels within each of the eight available bands. Frequency selection is made via microprocessor controller IC300, which interfaces with the user by means of the Group and

Channel switches, SW324 and SW325. The output of the synthesizer is a series of pulses that are integrated by a passive loop filter consisting of C532, R514, C533, R513, and C531 to produce the control voltage signal.

The VCO output is coupled to the RF buffer stage (Q600) by a matching network consisting of R602, C614, and L610. R600 and R603 provide base bias for the transistor, while R605 sets its operating current. RF choke L600 provides power and decoupling for the stage, in conjunction

25A1090 (Rev.3)