Connect your XG3 via an XG3 Data Cable to your personal computer.
If your computer does not have an available serial port, you may use a USB to Serial Adapter such as the Elecraft KUSB.
Choose the Personal Computer serial port that is connected to your XG3. Click the down arrow to show the list of available ports and then select the port you have connected to your XG3. See Finding the appropriate serial port for a USB to Serial Adapter if you're using a USB to Serial Adapter and are not sure which port to choose.
Click to update the list of available serial ports, which may be helpful if you plug in a USB to Serial Adapter after the program has started.
Reopens the serial port and verifies that the XG3 Utility can communicate with your XG3.
An XG3 in its boot loader, modems, null modem cables, and defective serial cables can echo whatever is sent to them. The XG3 Utility cannot tell what device is attached without sending a block of firmware. If firmware load fails on the first block (address x800), it is very likely that the communications cable is not correctly attached to your XG3, the cable is defective, or the wrong serial port has been chosen.