Hi Patrick,
Not necessarily. On Icom radios, that is a correct assumption. On other radios, it is the channel
used to connect the two RRC's. If one is using a CAT connection between them as the "twin"
configurations require, then COM0 becomes irrelevant. If using a radio that has a proprietary
connection between the two, such as the TS-480, then it becomes important. So your answer
is "it depends".
I assume that you are using a pair of TS-590's in twin mode? If so, then you are using COM2 to
connect the two over their CAT ports. So to enable CAT, you set COM1 to duplicate CAT by setting
it to mode 6 or mode 7 on both RRC's, depending upon how you want to use the CAT port(s).
73,
Mitch DJ0QN / K7DX