+ AA6YQ comments below
Dave I have an aftermarket USB to cat cable. it is about 12 years old and so could be bad... I am going to try the CT17 tomorrow ... but I have no idea how to test for a good com port other than shutting down DXLab and setting up something like mixw to see if that works. Let me see if any of my USB utilities will work on this..
+ Since Commander correctly controls your IC-7300, you can use IC-7300 to test your USB-to-CIV cable with the same COM port you're using with the IC-746.
+ There is a small risk that your USB-to-CIV cable is damaged in a way that damages the connected transceiver's internal CI-V port. I've not seen this happen with Icom transceiver and interfaces, but have seen it in other debugging scenarios.