Ye of little faith,

this is an inherent issue with any USB type communication device. That is why many of us prefer to use the Ethernet variety of motion controllers.

That said, you do not need to spend money on a controller, I am sure the UC300 is more than adequate.

So things to check/do just listed as they pop into my head:


1)Put a ferrite filter thingy on you USB cable if it does not already have one.
2)Ensure that the ground of the VFD is connected
3)Try to increase the distance between the VFD and the UC300/laptop
4)Plug the VFD directly to the wall socket
5)Ground your machine.

Seems you have already done the obvious and used shielded cable

Are you using a laptop to run the UC300? I seem to remember my USB data logger used to not like being on powered by a desktop, something to do with the 5V line being linked through to ground so it would pick up nearby motor noise and flake out