Analog monitors operate on one of 3 frequencies: 49MHz, 900MHz or 2.4GHz. They can have between 2 and 10 channels to choose from to minimize interference.
Digital monitors operate on one of 2 frequencies: 900MHz or 2.4GHz. They have no channels to choose from because they automatically scan for the clearest channel.
It is possible that the units simply need to be reset or paired.
1. Press the pairing button on the side of the receiver with a paperclip until the power button L.E.D. blinks and the range indicator turns on.
2. Press the pairing button on the back of the transmitter with a paperclip until the receiver range indicator turns off.