Raymarine forum

No, the ST60 instrument and the GPS are on different interfaces, Seatalk 1 and possibly NMEA 0183.

You can look at the back of your E120 Classic and see if anything is connected to the Seatalk HS port. With what you have explained so far, it should be unused.

I did look and there is indeed something connected to that port. It is a gray, small diameter cable. Could this have anything to do with the new Raystar antenna I mentioned earlier? I can send a photo of it if that would help.

I think I know what the small gray cable going into this port is. Might it be the ethernet connection to my PC running RNS?