Lectrosonics SMV-470 Miniature Wireless Audio Transmitter

To meet the demand for both extended operating range and extended battery life, the Lectrosonics SMV-470 Miniature Wireless Audio Transmitter offers selectable output power ranging from 50 to 100 and 250 mW. With higher power output, the operating range is improved at the expense of battery life. When range is not an issue, the power can be reduced to extend the battery life. The SMV-470 is compatible with the RM and RM2 remote control units for hands free setup and adjustment using audible tones delivered into the microphone from a tiny loudspeaker in the remote control unit. The transmitter can be put to sleep to conserve battery power during setup while the transmitter is buried deep inside costuming, then awakened for normal operation when the production begins. Other features include frequency and audio level adjustment and control lockout.

Digital Hybrid Wireless is a revolutionary new design that combines digital audio with an analog FM radio link to provide outstanding audio quality and the exemplary RF performance of the finest analog wireless systems. This overcomes channel noise in a dramatically new way, digitally encoding the audio in the transmitter and decoding it in the receiver, yet still sending the encoded information via an analog FM wireless link. This proprietary algorithm is not a digital implementation of an analog compandor. Instead, it is a technique which can be accomplished only in the digital domain. The process eliminates compandor artifacts, expanding the applications to include test and measurement of acoustic spaces and musical instruments.

The DSP-based design works with all Digital Hybrid receivers, and is backward compatible for use with Lectrosonics 200 and 100 Series and IFB receivers and some other brands of analog wireless receivers. The input section features the unique servo bias input circuitry with a standard TA5M type jack for use with electret lavaliere mics, dynamic mics, or line level signals. A DSP-controlled analog audio limiter is employed ahead of the first mic preamp to protect the entire audio chain from overload. The limiter has a range of more than 30 dB for excellent overload protection and a dual release envelope that makes the limiter acoustically transparent while maintaining low distortion. The limiter recovers quickly from brief transients, with no distorion. A water resistant control panel with LCD, membrane switches and multi-color LEDs make input gain adjustments, frequency and compatibility mode selection quick and accurate. The battery compartment accepts lithium or rechargeable AA batteries. The housings are machined from solid aluminum blocks to provide an extremely lightweight and rugged package. A special non-corrosive finish resists salt water exposure and perspiration in extreme environments.

High Power Output and Long Battery Life

Variable power provides the choice of maximum power output for extended operating range and interference suppression, or lower power output for extended battery life when operating in less demanding RF conditions.

Adjustable Low Frequency Roll-off

The low frequency roll-off can be set for 3 dB down points at 35, 50, 70, 100, 120 or 150 Hz to control subsonic and very low frequency audio content.

DSP-Based Pilot Tone & Compatibility

The DSP generated pilot tone eliminates the need for fragile crystals and allows a different pilot tone frequency for each of the 256 carrier frequencies in the tuning range of the wireless system. Individual pilot tones significantly reduce squelch problems in multichannel systems where a pilot tone signal can appear in the wrong receiver via intermodulation products. The DSP also offers compatibility modes to allow backward compatibility with all Lectrosonics IFB systems, 100/200 Series systems and analog receivers from some other manufacturers in addition to its native Digital Hybrid operating mode.

Input Limiter

A DSP-controlled analog audio limiter is employed before the analog-to-digital converter. The limiter has a range of more than 30 dB for excellent overload protection. A dual release envelope makes the limiter acoustically transparent while maintaining low distortion. The limiter recovers quickly from brief transients, so that its action is hidden from the listener, but recovers slowly from sustained high levels, to keep audio distortion low and preserve short term dynamic changes. The bicolor LEDs indicate limiter activity accurately to assist in setting the input gain for optimal signal to noise ratio and dynamic range.

Circulator/Isolator

The transmitter RF output circuit includes a specialized RF device called a "circulator/isolator" (or simply "isolator") using a magnetically polarized ferrite to allow RF signals to pass through to the antenna, but block them from coming backward into the transmitter output section. This greatly reduces RF intermodulation produced in the transmitter output stages when multiple units are used in close proximity (a few feet apart). The isolator also helps protect the output stage from electrostatic shock delivered to the antenna. Isolators are common in broadcast and commercial applications, but because of their high cost it is unusual to find them in wireless microphone systems.

GORE-TEX® Vent

In special circumstances it is possible for moisture to be pulled into the housing when a unit is moved from a warm, damp operating environment, turned off and stored in a cool place. As the warm air inside the unit cools a vacuum is created, pulling air in past the exterior of the housing, bringing moisture with it. A special vent in the battery door prevents a vacuum from being created by allowing air to pass but blocking the passage of water.