Both the 900MHz model 4520U USB Wireless Unit and the 2.4GHz 4620U USB Wireless Unit do not require any external power.
Even though there is a 2.1mm or 2.5mm barrel power connector on the unit, power is supplied to the USB Wireless Unit through the USB cable connected to the laptop or PC. There are three LEDs stacked above each other yellow above green above red. When the USB cable is plugged into the laptop or PC, the red led will illuminate.
The green LED above the red LED will flash when data is send to the USB Wireless Unit, then almost instantly, the red LED will flicker off then on when the data is sent out the antenna.
The Yellow LED above the green LED will flash when data is received and sent to the USB cable.
The stack of 3 green LEDs will illuminate to indicate the received signal strength, all three green LEDs illuminated is strongest receive signal strength.