shure_lx2_sm 电路图.pdf

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1、Shure Incorporated 222 Hartrey Avenue Evanston IL 60202-3696 U.S.A. LX Wireless System ?1999, Shure Incorporated Printed in U.S.A. 2510061 (CG) SERVICE MANUAL CHANGE NOTICE LX2 WIRELESS HAND-HELD TRANSMITTER Changes and corrections have been made to the Service Manual for the LX2 Hand-Held Transmitt

2、er. To up- date your Service Manual, remove the pages identified in the tables below and replace them with the pages attached to this Change Notice. Note that there are no changes to pages not specifically identified in the tables below. LX2 HAND-HELD TRANSMITTER SERVICE MANUAL REVISION HISTORY Rele

3、asePart NumberDate Code Original25A1006QH Revision 125B1006QL Revision 225C1006SC Revision 325D1006SI Revision 425D1006TF Revision 525D1006BB Revision 625D1006BK Revision 725D1006CG CHANGES EFFECTIVE JULY 10, 2003 REMOVE these pages from the LX2 Service Manual INSERT these new Revision pages into th

4、e LX2 Service Manual 3535 RadioFans.CN 收音机爱 好者资料库 Characteristics1 25D1006 (CG) Service Manual 25D1006 (CG) LX2 Hand-Held Transmitter Characteristics General The Shure LX2 Hand-Held Transmitter is part of a wireless system designed for public address, educational radio and television broadcast- ing,

5、 school and community theater productions, and similar applications. The LX2 is intended for use with the matching LX3 and LX4 receivers. Controls and Connectors Figure 1.Identification of Controls and Connectors 1.Grille 2.OFF/PWR power switch 3.Battery LEDs 4.ON/MUTE mic switch 5.Audio gain contro

6、l 6.Battery cup ? ? LX2/BETA 58 1 2 3 4 5 6 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 Brothers Inc. Licensing: Operation may require a user license. Frequency or power-output modifi

7、cations may violate this products approvals. Contact your countrys communications authorities. ?1999, Shure, Inc. Printed in U.S.A. RadioFans.CN 收音机爱 好者资料库 Shure LX2 Hand-Held Transmitter 2Characteristics25D1006 (CG) Circuit Description The Shure LX2 Hand-Held Transmitter contains three circuit boar

8、ds; an audio section, an rf section, and a microphone head interface board. It is intended for use with the matching LX3 and LX4 receivers. Audio Section Audio signals from the microphone head enter the transmitter via a printed circuit board (pcb) with spring contacts, which also interconnects the

9、audio and rf printed circuits. The audio signal next enters a preamplifier stage consisting of one section of operational amplifier (U102C). The voltage gain of this stage may be adjusted over a 40 dB range by means of an externally- accessible potentiometer (R125) to enable the user to compensate f

10、or variations in sound level at the microphone. The preamplified audio signal is then passed through a passive pre-emphasis network consisting of R142, C110, C111, R112, and R115, that has a pole at 63 microseconds and a zero at 12 microseconds. Audio Signal Compression The signal then enters the NE

11、571D integrated circuit compander (U101A). This provides 2:1 logarithmic compression of the audio signal. A lower noise floor is achieved by U102A. An internal potentiometer (R130) is provided for nulling system audio distortion. Operational amplifier U102B operates as a two-pole active low-pass fil

12、ter to restrict the bandwidth of the system to audio frequencies. Reverse Battery Protection and Low Battery Warning The NE571D also contains an identical second channel (U101B), which in this case is used to supply regulated, low-noise 5 Vdc bias to various audio and rf circuit points. Transistor Q

13、105 provides reverse battery protection to the circuit. Q110 drives a green LED (D103) that serves as a power ON indicator. Q107 drives an amber LED (D102) that provides a low battery warning signal to the user. Q106 and Q108 drive a red LED (D101) that serves as a final low battery indicator. Rf: D

14、omestic (FCC/IC) Processed audio enters R201, an internal potentiometer that is adjusted for 15 kHz deviation (100% modulation) with a 2.2 dBV, 1 kHz tone at the output of the audio section. The audio is then fed to varactor diode D201, which is part of the modulated oscillator-tripler stage (Q201).

15、 RadioFans.CN 收音机爱 好者资料库 Shure LX2 Hand-Held Transmitter Characteristics3 25D1006 (CG) The base-emitter circuit of Q201 operates as a crystal-controlled Colpitts oscillator in the 20 MHz region. Fundamental-mode crystal Y201 is tuned 10 kHz below series resonance by the series combination of frequen

16、cy-netting coil L201, diode D201, capacitor C203, and capacitor divider C206 and C207. Frequency Stability To ensure frequency stability with changes in battery voltage, regulated 5 Vdc bias is applied to the varactor diode and to the base of Q201. Temperature compensation is provided by C206 and C2

17、07. The collector circuit of Q201 is tuned to the third harmonic of the oscillator frequency (approximately 60 MHz) by means of L202 and C208. C210 couples rf energy to a second tuned circuit consisting of L203, C214, and C215, which also forms a capacitively-tapped voltage divider for matching into

18、 the base of Q202, operating as a buffer amplifier. Regulated dc bias is again employed to minimize changes in loading on the oscillator stage and stabilize drive levels. The collector circuit of Q202 is again tuned to the third harmonic of the oscillator frequency by L204 and C216. C219 couples rf

19、energy to another tuned circuit consist- ing of L205, C222, and C224, which also forms a capacitively-tapped voltage divider for matching into the base of Q203. Frequency Tripler The third stage (Q203) is operated as a frequency tripler with the collector circuit tuned to the output frequency (for e

20、xample, 180 MHz). In this case L206, C226, C229, L207, C230, and C232 perform tuning and impedance matching functions. As in the preceding stage, regulated dc bias is applied to the base circuit to stabilize the drive level, and the output is double-tuned to provide spectral purity. The final output

21、 stage (Q204) is operated as a tuned amplifier. Resistive loading on the input enhances stability. The output circuit consists of a tuned tank circuit (L209, C237, and C239) which also provides impedance matching to the output low-pass filter (C239, L210, and C241). L211 and C242 match the antenna t

22、o the filter. Stable Operation To promote stable operation, the LX2 is designed to minimize the production and radiation of spurious emissions and harmonic energy. In addition to the features described previously, the collector of each rf stage is separately decoupled from the 9 Vdc supply using fer

23、rite chokes, resistors, and bypass capacitors of the appropriate value. The base cir- cuits are similarly decoupled except that they use resistorcapacitor (RC) networks that are more appropriate, due to the higher impedance level. The use of surface mount components results in better perfor- mance b

24、ecause of a reduction in stray inductances and unwanted radiation from component leads. Double-sided printed circuit board construction improves groundplane performance. Shure LX2 Hand-Held Transmitter 4Characteristics25D1006 (CG) Rf: Euro (ETSI) Audio Input Processed audio enters R201, an internal

25、potentiometer that is adjusted for 15 kHz deviation (100% modulation) when the audio section provides a 2.2 dBV, 1 kHz tone. Oscillation The audio then goes to varactor diode D201, which is part of the modulated oscillator-tripler stage (Q201). The latters base-emitter circuit operates as a crystal-

26、controlled Colpitts oscillator in the 20 MHz region. Fundamental-mode crystal Y201 is tuned 10 kHz below series resonance by the series combination of frequency-netting coil L201, diode D201, capacitor C203, and capacitor divider C206 and C207. Frequency Stability To ensure frequency stability despi

27、te changes in the battery voltage, regulated 5 Vdc bias is applied to the varactor diode and to the base of Q201. C203, C206, and C207 provide temperature compensation. Tuned Circuits Stage 1: The collector circuit of Q201 is tuned to the third harmonic of the oscillator frequency (approximately 60

28、MHz) by L202, C208, C244, C210, L203, C214, C213, and C215. The latter components also form a capacitively-tapped voltage divider for matching into the base of Q202. The output is double-tuned to provide high spectral purity. Regulated dc bias is again employed to minimize changes in loading on the

29、oscillator stage and to stabilize the drive levels. Stage 2: Q202 operates as a buffer with the collector circuit tuned to the output frequency (for example, 60 MHz). In this case, L204, C216, C245, C218, L205, C222, C221, and C224 perform tuning and imped- ance-matching functions. As in the precedi

30、ng stage, regulated dc bias is applied to the base circuit to stabilize the drive level, and the output is double-tuned to provide spectral purity. Stage 3: Q203 operates as a frequency tripler, with the collector circuit tuned to the output frequency (for example, 180 MHz). In this case, L206, C226

31、, C227, C229, L207, C230, and C232 perform tuning and impedance-matching. Stage 4: Q204 operates as a tuned amplifier. Resistive loading on the input provides stability. The output circuit consists of a resonant tank circuit (L203 and C213) capacitively coupled to a low-pass filter (C219, L206, and

32、C218). C213 and C219 provide a capacitively-tapped voltage divider for matching into the low-pass filter. Shure LX2 Hand-Held Transmitter Characteristics5 25D1006 (CG) Final Output Transmitter: The transmitter can deliver up to +11.5 dBm (14 mW) to the antenna. No user adjustments permit this value

33、to be exceeded. Testpoint TP6 provides a termination point for the 50 output. C243 and L211 act as a series-resonating network for the battery, which acts as the antenna. The unit should be powered exclusively by a 9 Vdc dry battery. An alkaline type such as the Duracell MN1604 is recommended. Volta

34、ge Measurements With 9 Vdc applied to the unit, the following voltages should appear at the terminals of the output transistor: ?Vc = 8.83 Vdc ?Vb = .097 Vdc ?Ve = .32 Vdc ?Base current = 0.27 Adc ?Emitter current = 9.67 mAdc ?Collector current = 9.67 mAdc ?Power input = 87 mW The output power is +9

35、.5 dBm (8.9 mW) into a 50 load, at a frequency of 169.445 MHz. At the lowest acceptable battery voltage of 6 Vdc, the final collector current drops to 8.84 mAdc and the output power to +7.3 dBm (5.4 mW). Spurious Emissions To promote stable operation and to minimize the production and radiation of s

36、purious emissions and harmonic energy, the collector of each rf stage is separately decoupled from the 9 Vdc supply by ferrite chokes, resistors, and bypass capacitors. The base circuits are similarly decoupled, except for using resistor-capacitor (R-C) networks whose higher-impedance levels are mor

37、e appropriate. Power Section The transmitter delivers a maximum of +3 dBm (2 mW) ERP, to comply with ETSI Class 1 or 2 limits. There are no user adjustments which would permit this value to be exceeded. The low effective radiated power is due to the low radiation resistance of the battery antenna, w

38、hich is only a small fraction of a wavelength at this frequency. The transmitter is intended to be powered exclusively by a 9 Vdc dry battery (alkaline type recommended) such as a Duracell MN1604, which also serves as the antenna. The ground plane of the circuit board serves as an untuned counterpoi

39、se. Shure LX2 Hand-Held Transmitter 6Notes:25D1006 (CG) Notes: Shure LX2 Hand-Held Transmitter Preliminary Tests7 25D1006 (CG) Preliminary Tests Listening Test Before completely disassembling the transmitter, operate it to deter- mine whether it is functioning normally and try to duplicate the repor

40、ted malfunction. Refer to the products User Guide for operating instructions, troubleshooting, and specifications. Review any customer complaint or request, and focus the listening test on any reported problem. The following, more extensive, functional tests require partial disassembly. Functional T

41、ests Refer to the Disassembly section to partially disassemble the transmitter for the following functional tests. Use dc blocks at all rf outputs to protect test equipment. Shure LX2 Hand-Held Transmitter 8Preliminary Tests25D1006 (CG) Test Component Locations + R130 U101 U102 J101 J102 + R125 J101

42、 J102 L209 R217 Y201 C217C216 +9 V +9 V +5 V +9 V Audio Board (top) Low battery (RED) D101 Power (GREEN) D103 Head Board (front view) Rf Board (top) (FCC/IC) + J101 J102 Y201 Rf Board (top) (ETSI) L201 R201 C214 C222 C226 Gold-plated contacts C216 Power ON/OFF S101 Mic ON/OFF S102 Audio IN (from aud

43、io board) Gnd GndGnd Audio OUT (to rf board) Audio IN (from cartridge) +9 V (to cartridge) Audio IN (to audio board) I210 I2GN C240 Figure 2.Test Component Locations Shure LX2 Hand-Held Transmitter Preliminary Tests9 25D1006 (CG) Rf Tests SPECTRUM ANALYZER ? ? LX2 TransmitterSpectrum Analyzer Power

44、switch:PWRCenter frequency:transmitter frequency Mute switch:MUTESpan:30 MHz Reference level:+ 20 dBm Scale:10 dB/div Figure 3.Rf Functional Test Set-Up 1.Install a new 9 Vdc battery and turn on the LX2. 2.Measure the current drain: it should not exceed 35 mA. 3.Maximize the signal received on the s

45、pectrum analyzer by attaching a telescoping whip antenna. Then measure the near- field output power. It should measure ?3 dBm . 4.Verify that the carrier frequency of the transmitter varies from its nominal value by no more than ?6 kHz. 5.Check for an intermittent problem by shaking the transmitter

46、and tapping on it, keeping the transmitter a constant distance from the spectrum analyzer. Verify that the output power on the spec- trum analyzer shows no large and sudden drops in power level. It will, however, vary a few dB according to hand position. 6.Turn the LX2 OFF. Shure LX2 Hand-Held Trans

47、mitter 10Preliminary Tests25D1006 (CG) Audio Tests Check the Matching Receiver AUDIO ANALYZER RF SIGNAL GENERATOR 12.5 18.9 VDC ANTANT OUTPUTS HI Z BAL MICLINE POWER AB LX4 RECEIVER NOTE: DC VOLTAGES ARE PRESENT AT MOST RF TEST POINTS. USE A DC BLOCK ON THE RF SIGNAL GENERATOR TO PROTECT TEST EQUIPMENT. DC BLOCK LX4 ReceiverAudio AnalyzerRf Signal Generator Power switch:ONFrequency:1 kHzAmplitude:20 dBm Gain:MaxFilters:Modulation:1 kHz Squelch:MidLow-Pass (30 kHz):ONDeviation:15 kHz High-Pass (400 Hz):ONFrequency:LX2 operating frequency Figure 4.Matching Receiver Funct