SLX2 Wireless Transmitter Service Manual
25A1090
The Shure Model SLX2 is a µP (microprocessor) controlled frequency agile UHF handheld transmitter operating over the frequency range of 518 to 865 MHz (in eight different 24 MHz-wide frequency bands). The transmitter will operate for a minimum of 8 hours using two "AA" alkaline batteries. The User Interface includes "mode" and "set" buttons, and an LCD that displays battery status, group/channel, and transmitter/ receiver frequency synchronization. The SLX2 has a plastic enclosure, and utilizes an internal antenna for optimum range and reliability. This product is intended for use in entry-level presentation, installed, and performance markets.
SLX
mute select
3.Operating frequency programmable locally or from the receiver using a built-in IR link.
4.Designed for use with "AA" alkaline batteries (2 required). May also be used with rechargeable "AA" batteries. Note: battery condition indicator is calibrated for alkaline batteries and may not be accurate with rechargeable types. Electrical reverse battery protection is included.
©2006, Shure Incorporated 25A1090 (Rev.3)
1
2
SLX
3
4 |
mute |
select |
5 |
1Interchangeable microphone head (SM58 pictured)
2Power / Infrared (IR) / Mute indicator
Green: ready Amber: mute on
Flashing red: IR transmission in process Glowing red: battery power low
Pulsing red: battery dead (transmitter cannot be turned off until batteries are changed)
3LCD screen
4On-off / mute switch
Press and hold to turn on or off. Press and release to mute or unmute.
5Select switch
6IR port
Receives infrared beam to synchronize frequencies. When using multiple systems, only one transmitter IR port should be exposed at a time.
6
SLX
mute select
•0dB: For quiet to normal vocal performance.
•–10dB: For loud vocal performance.
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BIAS |
AUDIO |
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0dB |
-10dB |
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a
b
SLX
mute select
25A1090 (Rev.3) |
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a 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 |
5 |
1.Press and hold the select button until the GROUP and CHANNEL displays begin to alternate.
2.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.
3.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
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 infrared synchronization.
Indicates charge remaining in transmitter batteries.
Incompatible
MASTER LIST
GROUP CHANNEL
i8 i8
Incompatible
MASTER LIST
GROUP CHANNEL
i8 i8
Note: the transmitter cannot be used to change master list settings.
The INCOMPATIBLE warning indicates that the receiver and transmitter are transmitting on different frequency bands. Contact your Shure retailer for assistance.
25A1090 (Rev.3) |
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Deviation Trim |
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2-pole, |
and Tone Key |
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User Gain |
Pre- |
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Sum Amp |
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Control Switch |
VCA |
17kHz, |
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emphasis |
LPF |
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Audio Input |
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(mic head) |
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IR |
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Limiter |
RMS |
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Photodetector |
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Detector |
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LCD |
32.768 |
Microcontroller Tone Key |
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Compressor |
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kHz |
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Frequency |
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LCD |
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Synthesizer |
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Driver |
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control |
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Audio Muting |
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EPROM |
Channel |
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RF Muting |
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Select, |
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Power Mute |
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VCO (Carrier |
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Range) |
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LPF |
RF |
Pad |
RF |
Pad |
Loop |
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Amp |
0-4 dB (Band |
Amp |
0-4 dB (Band |
Filter |
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+5V DC |
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DC-DC |
Source |
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Frequency |
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Synthesizer |
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AA Battery |
Converter |
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Supply |
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16 |
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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) |
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network (D162) provides temperature compensation for changes in the VY, 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.
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.
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.
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-con- trolled 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) |
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with C600 - C604. The collector of Q600 feeds the power amplifier stage via an impedance matching network consisting of L602, C611, and C618.
The bias voltage for the RF power amplifier (Q601) is supplied by R601 and R604. Its operating current is controlled via emitter resistor R606. RF choke L601 provides power and decoupling for the stage, in conjunction with C605-C609. For Japanese systems only, the output power is trimmed via TR640. L603, C612, and L604 provide the output impedance matching into the low pass filter, which consists of L604, L605, L606, C615, C616, and C617. The low pass filter output couples to the battery antenna via C641 and L607. Connector CON640 and C613 are only used for Japanese (JB) units. Coupling capacitor C610 is used to ensure that both batteries are driven equally.
The transmitter is capable of delivering up to +15.0 dBm to the antenna (depending on band and country). During transmitter power-up and frequency selection, the RF output is muted by bringing the base of Q631 low, which removes bias from Q630 and shuts down power to the RF stages. The RF output is also muted during the transmitter power-down sequence. This is done so that the carrier signal will not interfere with other transmissions when the loop becomes unlocked.
Backlight
LED
RF Band |
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Power LED |
DC Level |
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LCD Driver
Battery DC (Rohm LCD
Level
BU9729k)
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Sythesizer |
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Power Mute |
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(National |
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VCO |
Button |
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Microprocessor |
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Semiconducter |
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LMX2335) |
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MC68HC908GR16) |
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RF Power |
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Softstart |
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Tonekey |
Shutdown |
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Squarewave |
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Infrared |
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EEPROM |
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Audio Mute |
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Tonekey |
Photodetector |
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93AA46 ) |
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25A1090 (Rev.3) |
6 |
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If TP_PB0 is held to TP_EGND, or logic level 0, at startup, the microcontroller will enter ATE Mode. To ensure proper operation, TP_PA0 and TP_PA1 should be held to TP_EGND at startup. In ATE Mode, each band has a three test frequencies that are controlled by the logic levels at test points TP_PA0 and TP_PA1.
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Frequency |
TP_PA0 |
TP_PA1 |
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Low |
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Center |
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High |
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Test Frequencies (MHz) |
H5 |
J3 |
JB |
L4 |
P4 |
Q4 |
R5 |
S6 |
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SLX2 |
Low |
518.400 |
572.400 |
806.125 |
638.400 |
702.100 |
740.125 |
800.525 |
838.100 |
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Center |
529.500 |
583.500 |
807.500 |
649.500 |
714.000 |
746.325 |
810.275 |
851.300 |
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High |
541.800 |
595.800 |
809.750 |
661.800 |
725.900 |
751.875 |
819.800 |
864.800 |
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SLX2 |
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RA |
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RB |
R319 |
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R320 |
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25A1090 (Rev.3) |
7 |
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RF BAND |
Rb |
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TP_RFBAND(+/- 0.10V) |
H5 |
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1.00k |
0.30V |
J3 |
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2.99k |
0.76V |
L4 |
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4.99k |
1.10V |
R5 |
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7.50k |
1.41V |
S6 |
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12.10k |
1.81V |
P4 |
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18.2k |
2.13V |
Q4 |
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30.1k |
2.48V |
JB |
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49.9k |
2.75V |
Note: Voltages are calculated with a 3.30V (+/- 0.10V) reference from the power supplies. If power section supports less than 3.30V, thresholds need to be adjusted.
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Continuous Operation Battery Thresholds |
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BATTERY_A2D |
RF Level |
Display |
Logic |
Voltage (V) |
Measured @ 3V |
- dBC |
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block battery clips |
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- dBC |
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- dBC |
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-8 dBC |
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Note: There is a dead battery lock voltage set at 2.30 Volts. If the transmitter is powered on with a voltage of less than 2.30 Volts, the system will lock, forcing the user to either recharge or replace the batteries. During the dead battery lock out, the battery gauge is empty and the red led flashes.
25A1090 (Rev.3) |
8 |
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25A1090 (Rev.3) |
9 |
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Spectrum analyzer or power meter |
HP8590L/Agilent E4403B/Agilent E4407B |
Digital multimeter |
Fluke 87 |
Audio Analyzer |
HP 8903B |
Frequency Counter |
HP 53181/HP 5385A |
Power Supply |
Power Supply must be able to supply 3Vdc |
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with an internal ammeter. |
Shielded test lead |
Shure PT1838F |
BNC (Male) to BNC (Male) cable (1) |
Shure PT1838A |
UA820 Antenna |
Frequency Dependent |
Audio Test Head |
PT1840 |
Brass Ring |
PT1838Y |
3.Connect the (+) terminal of the power supply through a milliammeter to the (+) battery terminal and the (-) power supply terminal to the (-) battery terminal.
1.Power unit ON.
1.Adjust power supply to -3.0 ± 0.1 V dc.
•TPBATT+ (Battery input) = 3 ± 0.2 Volts
•TP5V (Power Converter) = 5 ± 0.2 Volts
•TP3.3V (Power Converter) = 3.3 ± 0.2 Volts
•TPA1 (Audio Preamp) = 2.5 ± 0.2 Volts
•TPA3 (Tone Key Summing Amp (IC150 Pin 14)) = 2.5 ± 0.2 Volts
•TPVREF (IC100 Pin 5) = 2.5 ± 0.1 Volts
25A1090 (Rev.3) |
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•Frequency = 1 kHz
•Amplitude = -20 dBu
•Filters = 30 kHz LPF
2.With the audio analyzer, probe TPA2 (top side), it should read -3.4dBu ± 0.5dB. Record this level using the Ratio button. This level will be used as your reference level for the following test.
3.Change the generator's frequency to 100Hz and measure the level at TPA2 to be -2.2dB ± 0.2dB relative to the 1kHz reference level.
1.Set the audio generator frequency to 1kHz with an amplitude of -20.0dBu.
1.Choose any group and channel free of interference. Using a spectrum analyzer with the appropri- ate-band UA820 antenna, measure the approximate near field radiated power as follows:
•SPAN=100 MHz
•REF LVL=10dBm
•FREQUENCY=(Look at tables on pages 18 thru 23)
2.Find transmitting carrier on the spectrum analyzer with a span of 200 kHz. Use the "Peak Search, Marker Delta, Next Peak" soft-keys on the analyzer.
3.Measure the 32.768 kHz tone key level to be -21 dBc ± 1.5 dB.
5.Measure the 32.768 kHz tone key level to be -14 dBc ± 1.5 dB.
2.Set up the HP-8591E spectrum analyzer to measure Occupied Bandwidth with the following settings:
•Percentage Power = 99.5%
•Channel Spacing = 250 kHz
•Bandwidth = 110 kHz
2.Measure Extended Adjacent Channel Power to be less than -60 dB.
IF ALL TEST PASSED, THIS MEANS THE UNIT IS PROPERLY FUNCTIONING, AND
NO ALIGNMENT IS REQUIRED.
25A1090 (Rev.3) |
11 |
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