This is a two pack of U4 transmitters and receivers operating in the 2.4 GHz range. I'm including a decent case and two XLR extenders. The latter are useful if you are plugging the transmitter directly into a "busy" PA board. I used these for about 20 gigs over the course of a year and they served me well. My wireless needs have changed, however, so I'm putting these up for sale. They are in great condition. Here is some info from the company:

• Efficient Power Circuit and Listening Effect: Rechargeable Lithium Battery,5 hours of battery life,comes with power cable,ensures great performance for your every show.Built-in Limiter circuitry eliminating distortion under excessive input levels. Front panel 1/4-inch monitoring has the headphone jack.it can replace traditional complex sound monitoring equipment,achieve admirable listening effect 
• Less than 5ms Latency: Simultaneous broadcasts on 6 channels no-interference, Less than 5ms Latency,Up to 107 dB signal-to-noise ratio provides clear, detailed audio at any volume. High Resolution 24-bit/48kbps audio. Broad 20Hz-20KHz frequency response, Dynamic Rang 107 dB