Shure Wireless Microphone Systems Operation Manual
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Shure Wireless Microphone Systems Operation Manual

Wireless microphone systems operation guide
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A Shure Educational Publication
Selection
and
Operation
of
Wireless
Microphone
Systems
Wireless
Microphone Systems
By Tim Vear
2
ND
EDITION

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Summary of Contents for Shure Wireless Microphone Systems

  • Page 1 A Shure Educational Publication Selection Operation Wireless Microphone Systems Wireless Microphone Systems By Tim Vear EDITION...

  • Page 2: Table Of Contents

    System Checkout and Operation ..43 Troubleshooting Wireless Microphone Systems ..44 Troubleshooting Guide ....45 .

  • Page 3: Introduction

    The scope of this guide is limited to wireless microphone systems used in audio applications. The reader is presumed to be somewhat familiar with basic audio.

  • Page 4: Part One

    Part One: Wireless Microphone Systems: How They Work H A P T E R Basic Radio Principles RADIO WAVE TRANSMISSION Radio refers to a class of time-varying electromagnetic fields created by varying voltages and/or currents in certain physical sources. These sources may be "artificial,"...
  • Page 5 H A P T E R Basic Radio Principles The speed of radio waves (through a vacuum) is equal to approximately 3 x 10 meter/second, or about 186,000 miles/ second. This is also known as the "speed of light," since light is just one part of the radio spectrum.

  • Page 6: Radio Wave Modulation

    H A P T E R Basic Radio Principles ambient radio "noise," that is, general radio energy produced by many natural and man-made sources across a wide range of frequencies. The strength of ambient radio noise is relatively constant in a given area, that is, it does not diminish with distance.

  • Page 7: Chapter 2 Basic Radio Systems

    The output of the receiver is typically monitored through headphones or loudspeakers. It may feed a portable audio or video recorder. wireless systems for in-ear-monitors, (IEMs) interruptible foldback systems (IFB), assistive listening, simultaneous translation, and various instructional uses.

  • Page 8: Transmitter: General Description

    H A P T E R Basic Radio Systems microphone level, and usually low impedance. Since the "wireless" part of the wireless microphone only serves to replace the cable, ideally, the characteristics and performance of a particular microphone should not change when used as part of a wireless microphone system.

  • Page 9: Transmitter: Audio Circuitry

    It is useful to describe these elements to gain some insight to the overall performance and use of wireless microphone systems. (See Figure 2-3.) TRANSMITTER: AUDIO CIRCUITRY The first part of the typical transmitter is the input circuitry.

  • Page 10: Transmitter: Radio Circuitry

    H A P T E R Basic Radio Systems A variation that is found in a few compander designs is to divide the audio signal into two or more frequency bands. Each band is then pre-emphasized and compressed independently. In the receiver, de-emphasis and expansion are applied separately to these same bands before combining them back into a full-range audio signal.

  • Page 11: Receiver: General Description

    attached.
  • Page 12 H A P T E R Basic Radio Systems is not tuneable. Filter circuits of various types ranging from simple coils to precision "helical resonators" are used in front end filters. The second receiver section is the "local oscillator" (usually abbreviated as "LO"). generates a constant radio frequency that is related to the frequency of the received radio signal but differs by a "defined amount."...

  • Page 13: Receiver: Audio Circuitry

    (level and impedance) for connection to an external device such as a mixer input, a recorder, headphones, etc. Typically, better receivers will include a balanced output that can be switched between line level and microphone level. Unbalanced outputs are usually provided as well.

  • Page 14: Receiver:antenna Configuration

    H A P T E R Basic Radio Systems Level RF signal and noise Radio Frquency Figure 2-14: threshold squelch Noise muted Level unmuted Audio Frequency Figure 2-15: noise squelch Level 20 Hz 20 kHz Audio Frequency Figure 2-16: tone key squelch This effectively prevents the possibility of noise from the receiver when the desired transmitter signal is lost, even in the presence of a (non-tone-key) interfering signal at...

  • Page 15: Receiver: Diversity Techniques

    H A P T E R Basic Radio Systems Figure 2-18: multipath These multiple paths result in differing levels, arrival times and phase relationships between the radio waves. The net received signal strength at any location is the sum of the direct and reflected waves.
  • Page 16 H A P T E R Basic Radio Systems Figure 2-20: passive antenna combining Figure 2-21: antenna phase switching Figure 2-22: antenna switching Figure 2-23: receiver switching Figure 2-24: receiver combining The next variation, "antenna switching diversity," again consists of a single receiver with two antennas. The receiver includes circuitry that selects the antenna with the better signal according to an evaluation of the radio signal.

  • Page 17: New! Antennas

    H A P T E R Basic Radio Systems output will usually consist of a mix of the two audio sections. In the case of loss of reception at one antenna, the output is chosen from the other section. Excellent dropout protection is obtained with no possibility of switching noise since the diversity circuit is essentially an intelligent panpot, not a switch.
  • Page 18 H A P T E R Basic Radio Systems In all of these designs, the radio wave pattern emitted by the 1/4 wave antenna is omnidirectional in the plane perpendicular to the axis of the antenna. For a vertically oriented 1/4 wave antenna the radiation pattern is omnidirectional in the horizontal plane, which is the typical case for a trailing wire antenna.

  • Page 19: New! Antenna Cable

    Figure 2-27: examples of remote receiver antennas ANTENNA CABLE An important but often overlooked component of many wireless microphone systems is the antenna cable. Applications in which the receiver is located away from the transmitter vicinity and/or within metal racks will require the use of remote antennas and connecting cables.
  • Page 20 H A P T E R Basic Radio Systems usually operate at "unity" gain overall, that is, no net amplification occurs. Though a multi-coupler is generally a separate acces- sory, some receiver designs are equipped with internal antenna distribution when multiple receiver sections are incorporated in the same chassis such as modular or card-cage systems.

  • Page 21: Wireless System Operation

    54-72 MHz is occupied by VHF television channels 2-4. The 72 MHz area is used by "assistive listening" type wireless microphone systems. 76-88 MHz is assigned to VHF television channels 5 and 6. At the top, 88-108 MHz is the commercial FM radio broadcast band.

  • Page 22: Uhf

    UHF VS. VHF Like the VHF region, the UHF region contains several bands that are used for wireless microphone systems. However, certain physical, regulatory, and economic differences between VHF and UHF regions should be noted here.

  • Page 23: New! Frequency Selection

    THE UHF BAND The low-band UHF range of frequencies may be con- sidered as two overlapping bands: low (450-536 MHz) and high (470-806). The primary users of these bands are business services such as land mobile radio and pagers (450-536 MHz) and UHF television channels 14-69 (470- 806 MHz).

  • Page 24: System Compatibility

    The first class of interactions is the more important one and may occur in any group of wireless microphone systems. It is also the one more cumbersome to calculate. The second class of interactions is less problematic and is also relatively easy to predict.

  • Page 25: Internal Frequency Interactions: Lo, If, Crystal Multipliers

    IM products is best left to computer programs. The complexity increases exponentially for additional systems: a group of 10 wireless microphone systems involves thousands of calculations. See Appendix 1 for details on calculation of IMD products.
  • Page 26 H A P T E R Wireless System Operation received signal by an amount equal to the intermediate frequency (IF). Specifically, the operating frequency is above the local oscillator frequency by an interval equal to the IF. When these two frequencies are applied to the mixer section (a non-linear circuit) one of the output frequencies of the mixer is this difference frequency (the IF), which is the tuned frequency of the subsequent IF stage filters.

  • Page 27: Non-System Radio Interference

    H A P T E R Wireless System Operation multipliers. However, both types of transmitters can produce other spurious emissions due to power regulating circuitry, parasitic oscillations, carrier harmonics, etc. These emissions can all be controlled through careful design. It can be seen that the calculation of both local oscillator conflicts and image frequencies depends on the intermediate frequency (IF) of the receiver while calculation of crystal harmonics depends on the number of multipliers...
  • Page 28 Chicago has active high-band VHF TV channels 7, 9, and 11. Therefore, a suitable setup for use there would include wireless microphone systems on frequencies corresponding to TV channels 8, 10, and/or 12. If this setup is taken to Milwaukee, which has TV...
  • Page 29 H A P T E R Wireless System Operation DTV VS. WIRELESS SYSTEMS In the United States, the Federal Communications Commission (FCC) is currently supervising the transition of broadcast television from its traditional analog format to an all-digital format (DTV). commission is also mandated to increase efficient use of TV spectrum and to increase the amount of spectrum available for public safety and other wireless services.

  • Page 30: Broadcast Radio

    H A P T E R Wireless System Operation BROADCAST RADIO High-band VHF wireless FM systems are not generally subject to interference from commercial AM or FM radio stations. Both bands are well below the VHF band and in particular, these systems are not typically sensitive to moderate AM signals.

  • Page 31: Spread Spectrum Transmission

    Wireless System Operation SPREAD SPECTRUM TRANSMISSION A transmission technique that may have application to wireless microphone systems is known as "spread spectrum." The object of this technique is to improve performance by reducing interference effects and increasing efficiency of band utilization.

  • Page 32: Range Of Wireless Microphone Systems

    H A P T E R Wireless System Operation Important transmitter characteristics are power output and antenna efficiency. Maximum power is limited by government regulations and battery capability. Antenna efficiency is limited by size and design. Recall that the efficiency of typical wireless transmitter antennas is fairly low, about 10% or less for VHF.

  • Page 33: New! Digital Wireless Systems

    H A P T E R Wireless System Operation width than wireless microphones. Even so, bandwidth limitations necessitate the use of companders to achieve acceptable dynamic range in most high quality analog wireless systems. The bandwidth required for a high fidelity digital wireless system depends on the amount of digital information transmitted and the transmission rate.

  • Page 34: Operation Of Wireless Systems Outside Of The U.s

    H A P T E R Wireless System Operation OPERATION OF WIRELESS SYSTEMS OUTSIDE OF THE U.S. Allocation and regulation of radio frequencies is supervised by specific government agencies in each country, with the result that allowable (legal) frequencies and frequency bands differ from country to country.

  • Page 35: Wireless System Selection And Setup

    Part Two: Wireless Microphone Systems: How To Make Them Work H A P T E R Wireless System Selection and Setup SYSTEM SELECTION The proper selection of a wireless microphone system consists of several steps based on the intended application and on the capabilities and limitations of the equipment required for that application.

  • Page 36: Crystal Controlled Vs

    H A P T E R CRYSTAL-CONTROLLED VS. FREQUENCY SYNTHESIS Crystal controlled wireless units can be designed with wide audio frequency response, low noise, low distortion, and relatively long battery life. They are the most cost- effective choice for fixed frequency applications involving a moderate number of simultaneous systems.
  • Page 37 Microphones and input cables supplied by a manufacturer with a given wireless microphone system can be assumed to be compatible with that system. However, they may not be directly compatible with wireless microphone systems from other manufacturers. At a minimum, a connector change is often required.

  • Page 38: System Setup: Receivers

    H A P T E R Mixers and playback devices produce line level outputs. These sources typically have low-to-medium output impedance and may be balanced or unbalanced. They can sometimes be interfaced with a simple adapter cable. However, these high level input sources often require additional (external or internal) attenuation to prevent overload of the transmitter input, which is usually expecting a mic-level signal.
  • Page 39 H A P T E R udio Interface Here we will discuss the sound system interface. Remember that the basic function of a wireless microphone system is to replace the connecting cable between the source and the sound system. In the typical case, the output of the wireless receiver will resemble the output of the original source both electrically and physically.
  • Page 40 H A P T E R The threshold type squelch adjustment procedure is: Turn the transmitter power off to eliminate the desired signal. Turn on all associated equipment in nearby locations to create the "worst-case" signal condition. Set the receiver volume control to minimum to avoid excessive noise in the sound system.

  • Page 41: System Setup: Receiver Antennas

    H A P T E R SYSTEM SETUP: RECEIVER ANTENNAS Setup of receiver antennas involves first the antenna-to- receiver interface and then antenna placement. simplest case is a receiver with the antenna(s) permanently attached. The antenna is typically a quarter-wave telescoping or possibly "rubber ducky"...

  • Page 42: System Setup: Batteries

    H A P T E R SYSTEM SETUP: BATTERIES Always use fresh batteries of the correct type in the transmitter and/or receiver. Most manufacturers recommend only alkaline type batteries for proper operation. Alkaline batteries have a much higher power capacity, more favorable discharge rate and longer storage life than other types of single-use batteries such as carbon- zinc.

  • Page 43: Troubleshooting Wireless Microphone Systems

    Show Operation: 1) Again, verify good batteries in all transmitters.

  • Page 44: Troubleshooting Guide

    H A P T E R TROUBLESHOOTING WIRELESS MICROPHONE SYSTEMS Even when wireless microphone systems appear to be properly selected and set up, problems may arise in actual use. While it is not practical here to offer comprehensive solutions for all possible situations some general guidelines are suggested.

  • Page 45: Chapter 5 Application Notes

    H A P T E R Application Notes Following are some suggestions on wireless microphone system selection and use for some specific applications. Each section gives typical choices and setup for microphones, transmitters and receivers as well as a few operating tips. PRESENTERS The most common wireless choice for presentations is a lavaliere/bodypack system, which allows hands-free use...

  • Page 46: Vocalists

    H A P T E R Application Notes Occasionally it is found that certain wireless microphone systems do not initially work well with certain instruments. Symptoms may include poor frequency response, distortion or noise. In most cases this can be traced to an impedance or level mismatch between the two.

  • Page 47: Aerobic/Dance Instruction

    H A P T E R Application Notes AEROBIC/DANCE INSTRUCTION The microphone is most often a headworn type, with a unidirectional element. This will give the best results for feedback control and overall sound quality. A lavaliere microphone may be used if gain-before-feedback is not a problem but it will not have the same sound quality as a headworn type.

  • Page 48: Worship

    It is not unusual to use as many as 30 simultaneous wireless microphone systems in a professional musical theater production. This number can only be handled with systems operating in the UHF range.

  • Page 49: Film/Videography

    H A P T E R Application Notes FILM/VIDEOGRAPHY Film and videography applications usually call for lavaliere/ bodypack wireless microphone systems to minimize the visibility of the microphone. Handheld transmitters may also be used when visual appearance is not anissue. However, the receivers may be either fixed or portable.

  • Page 50: New! Point-To-Point Wireless

    H A P T E R Application Notes Lavaliere microphones will require a bodypack transmitter. If a desired handheld microphone model is available in a wireless version it can be used directly. Since most handheld transmitters use unidirectional microphone elements a plug-on transmitter may be necessary for use with handheld omnidirectional microphones or other wired hand-held models.
  • Page 51 H A P T E R Application Notes Figure 5-1: point-to-point using a wireless microphone system Using wireless in-ear monitors for point-to-point A wireless in-ear monitor system (IEM) can also be used as a point-to-point system with only one modification at the receiver.
  • Page 52 Special connectors and/or adapters may also be necessary in some cases. For moderate distance, single channel applications may use wireless microphone systems for good results. Multi-channel, especially stereo, transmission may benefit from the IEM approach. Longer distance uses will require directional antennas for wireless microphone receivers or for IEM transmitters.

  • Page 53: Conclusion

    As wireless microphone systems evolve it is expected that some of the details presented here may become less critical in their day-to-day use. To...

  • Page 54: Appendix A: Calculation Of Intermodulation Products

    E F E R E N C E Appendix A CALCULATION OF INTERMODULATION PRODUCTS The simplest IM products that can occur between any two operating frequencies (f1 and f2) are the sum of the two frequencies and the difference between the two frequencies: f1 + f2 (sum) f1 - f2...
  • Page 55 E F E R E N C E Appendix A For determining compatibility of three frequencies (200 MHz, 195 MHz and 187 MHz in this example) the significant combinations become: Three-Transmitter Intermodulation Calculation Product f1 (original frequency) f2 (original frequency) f3 (original frequency) f1 + f2 - f3 f1 - f2 + f3...

  • Page 56: Eference Nformation

    E F E R E N C E Appendix B US TELEVISION CHANNELS Channel VHF Low Band VHF High Band UHF Band N F O R M A T I O N (Analog Components) Band Video Chroma 54-60 55.25 58.83 60-66 61.25 64.83...

  • Page 57: Glossary Of Terms And Specifications

    E F E R E N C E Glossary Absorption the weakening of radio wave strength by losses in various materials audio frequencies, typically 20-20,000 Hz. amplitude modulation Ambient local or background, ie. ambient noise Amplitude magnitude or strength of a signal or wave AM rejection ability of an FM receiver to reject signals from AM transmitters and/or AM noise from electrical devices...
  • Page 58 E F E R E N C E Glossary Field a distribution of energy in space, ie. electric, magnetic, sound Field strength the amplitude of a field at a given point, measured in volts per meter for electric energy frequency modulation Frequency a measure of the rate of variation of a wave or signal Frequency agile...
  • Page 59 E F E R E N C E Glossary Narrow band an FM signal in which the deviation is much less than the modulating frequency Noise undesirable random audio or radio energy Operating frequency the final output frequency of a transmitter or the tuned frequency of a receiver Oscillator a circuit that produces a continuous periodic output...

  • Page 60: Included Illustrations

    E F E R E N C E N F O R M A T I O N Illustrations Included In This Booklet...

  • Page 61: Suggested Reading & Biography

    E F E R E N C E Suggested Reading Suggested readings for more information on radio technology: • Solid State Radio Engineering, H. Krauss, C. Bostian, F. Raab (J. Wiley & Sons, 1980) • Introduction to Communication Systems, F. Stremler (Addison-Wesley, 1982) •...
  • Page 62 Additional Shure Publications Available: These guides are available free of charge. To request your complimentary copies, call one of the phone numbers listed below. • Selection and Operation of Personal Monitor Systems • Audio Systems Guide for Video Production • Audio Systems Guide for Houses of Worship •...

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