Krassyg,

Is there an opportunity to keep the microphone receiver near the singer? Depending on the cable run length, you may need an amplifier in the antenna circuit.

Also, the microphones that I've seen supplied with Karaoke machines are trash. They sound bad, overload easily, have bad battery run times, and intermittent charging contacts. I suggest that you substitute a good professional wireless microphone. A professional microphone may have enough range without messing with remote antennas.

If you are working with an iPad App, make sure that you have good WiFi coverage in the operating area.