If you're having difficulties getting the USB connection to the NDC-4
working, or if it has been working and now isn't, there's a few useful
tests you can perform before contacting our support team which can be found here: https://www.actisense.com/knowledge-base/nmea-0183/ndc-4/usb-not-working/
The USB lead must not be connected to a PC or laptop while the NDC-4 is
powered via a battery connected to the "BATT" terminals. Doing so will
create a ground loop and damage the NDC-4's USB chip. The USB
connection is more than capable of supplying the NDC-4 with enough power
to operate.