Lectrosonics HM Digital UHF Wireless Plug-On Microphone Transmitter, Block 21 Frequency, 100mW RF Power Output, 300Ohms Input Impedance

The Lectrosonics HM Digital UHF Wireless Plug-On Mic Transmitter (Block 21 Frequency) features a DSP-based design that allows the transmitter to operate in its native Digital Hybrid Wireless mode, Lectrosonics 200 Series, 100 Series, IFB product groups, plus two modes for compatibility with analog receivers from other manufacturers. A unique multi-voltage phantom power feature allows the transmitter to be used with virtually any microphone, including high-current condenser types, expanding its usefulness in high-end applications such as motion picture production.

The transmitter provides 256 frequencies in standard frequency blocks, selected with two rotary switches on the side of the housing. The input amplifier uses an ultralow noise op-amp for quiet operation. It is gain controlled with a wide range dual envelope limiter, providing over30 dB of headroom above full modulation. A 24-bit A-D converter digitizes the audio, then filters supersonic noise above 21 kHz. The resulting signal is encoded with a proprietary algorithm to produce an analog data signal for RF transmission. The underlying RF link is an optimized FM system with +/-75 kHz wide deviation for a high signal to noise ratio.

The antenna is formed between the lower housing of the transmitter and the attached system. It functions as a dipole radiator when attached to a hand-held microphone and somewhat like a ground plane antenna when connected into a mixer. The conical shaped collar on the input coupler is made of DuPont Delrin to improve the ERP of the antenna in the uppermost frequency blocks.

DSP-Based Pilot Tone & Compatibility
The DSP eliminates the need for fragile crystals, plus it allows a different pilot tone for each of the 256 frequencies in the tuning range of a system's frequency block. Individual pilot tones virtually eliminate squelch problems in multichannel systems where a pilot tone signal can appear in the wrong receiver via inter modulation products. A circulator/isolator in the output stage further ensures against inter modulation interference.

Outstanding Audio Performance
The audio performance of the overall hybrid system is depicted in the graph below. Distortion in the overall system is extremely low over the entire audio bandwidth. The battery compartment door is hinged to the housing and remains attached to the transmitter when opened. It securely latches in place and applies pressure to the batteries when closed. The two AA batteries are connected in series through a conductive plate on the door. Setup and adjustments are made with the control panel membrane switches and LCD. The transmitter can be powered up without the transmitter output enabled to allow frequency adjustments without causing interference to other wireless systems nearby. The switches can also be bypassed to prevent accidental changes. Dual color LEDs indicate audio input level and the power LED changes color under low battery condition.