JVC RX-D Series Training Book page 101

USB WIRE OR WIRELESS
3/5
USB transmitter
User ID Learning Function
To ensure security, the wireless USB transmitter and the receiver share a specific
"user ID". This means devices without the same ID cannot receive signals from
the transmitter. And when you replace the transmitter, "User ID Learning
Function" would be convenient. This function lets you easily set up a new user ID,
so that the unit can receive signals from the new transmitter.