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WMS61
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WMS81
Wireless Microphone
Systems
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Introduction: The art and science of wireless microphone design have progressed in recent years to a point where reliable and flexible performance can be taken for granted in even the most complex venues. What remains is for this level of performance to become available at competitive prices and with easier setup requirements. AKG’s new WMS 61 and 81 wireless systems go a long way toward achieving these goals. The AKG WMS61 and 81 systems embody a number of technical attributes contributing to i
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FM has been used for broadcast transmission of high quality audio since the mid-1950s, and its primary advantages are wide audio bandwidth and relative freedom from external electrical disturbances as compared to AM (amplitude modulation). The chief factors that determine the ultimate performance characteristics of an FM system are RF signal strength at the receiver and the modulation index (FM frequency deviation divided by modulating frequency) of the signal at the transmitter. In time, the tr
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Noise Considerations: Monophonic FM broadcast transmission normally has a very high signal-to-noise ratio because of relatively high signal strength and high modulation index. In the wireless microphone area, where we are “crowding” many channels into a relatively small radiated bandwidth, the usable signal-to-noise ratio is about 60 dB — which is not good enough for critical sound reinforcement applications. It is customary to “enhance” this performance through the use of some kind of code/deco
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Another technique for minimizing noise under marginal operating conditions is known as squelching. When the level of the incoming RF signal drops below a certain threshold, the system becomes prone to interference and may even pick up spurious signals. In older systems, the squelching threshold is a manual adjustment. The WMS 61 and 81 systems use a pilot tone sent from the from the transmitter, which “instructs” the receiver to adjust its reception level accordingly so that noises due to improp
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7. Color coded rings (part number CCS-1): Included in the package is a set of color coded rings and matching rectangular snap-on color chips. These accessories help you keep track of which microphone corresponds to which receiver. For example, you can replace the black ring (the one you removed earlier) with the yellow ring, and snap its corresponding yellow rectangular chip on the lower front center of the receiving unit which is tuned to the same frequency. The color coded ring on the handheld
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3. Mute indicator: When this red status light is on, the system is muted, indicating low or no RF signal from the transmitter. The squelch action operates with a pilot tone from the transmitter and requires no manual adjustment at the receiver. It is the level of this signal that automatically mutes the system, preventing a rise in noise when the RF signal is low or non-existent. 4. RF level: This consists of a set of 5 LED status lights. When RF signal strength is high, all five are lit, and p
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Trying Out the System: A Typical Setup: Now that you have been introduced to the basic functions of the WMS 61 and 81 units, let’s proceed with a typical setup. We’ll choose the bodypack and use it with a clip-on lapel microphone such as the AKG Model CK 77 WR-L. (The L in the model number indicates that this model has the proper locking-type plug-in jack for wireless use.) Mount the small microphone element onto the lapel clip by gently pushing the wire just below the microphone capsule into on
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Using Handheld Transmitters: The same setup routine and precautions as we used for the bodypack apply here as well. Since a given handheld transmitter may be used by a number of speakers it is recommended that the initial checkout be made using the loudest of the speakers to ensure that the system can handle those maximum speech peaks. Softer talkers will then require that the reinforcement system operator raise input levels at the console as required. General Usage: As with all wireless syste
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Specifications SR61 receiver: PT61 bodypack transmitter: Audio bandwidth: 50 Hz to 20 kHz Receiver type: Diversity Modulation method: FM Antenna inputs: 2 x 50-ohm BNC sockets Radiated RF power: 10 mW Modulation type: FM Input sensitivity: Typical -95 dBm Frequency stability: ±10 ppm Squelch threshold: Automatic, using pilot tone Antenna: Flexible, quarter-wave wire (32.678 kHz) Rated deviation: ±30 kHz Audio bandwidth: 50 to 20 kHz Signal-to-noise ratio: Typical 50 dB (A weighted) THD at 1 kHz
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Specifications PT81 bodypack transmitter: SR81 receiver: Audio bandwidth: 50 Hz to 20 kHz Receiver type: Diversity Modulation method: FM Antenna inputs: 2 x 50-ohm BNC sockets Radiated RF power: 10 mW Modulation type: FM Frequency stability: ±10 ppm Input sensitivity: Typical -95 dBm Antenna: Flexible, quarter-wave wire Squelch threshold: Automatic, using pilot tone (32.678 kHz) Rated deviation: ±30 kHz Audio bandwidth: 50 to 20 kHz Signal-to-noise ratio: Typical 50 dB (A weighted) THD at 1 kHz:
