Possible interference with or, more often, from other radio equipment or other radio microphones, though models with many frequency-synthesized switch-selectable channels are now plentiful and cost effective. Operation time is limited relative to battery life; it is shorter than a normal condenser microphone due to greater drain on batteries from transmitting circuitry, and from circuitry giving extra features, if present. Noise or dead spots (places where it doesn't work, especially in non-diversity systems) Limited number of operating microphones at the same time and place, due to the limited number of radio channels (frequencies).