To report back, I managed to block the RFI causing high-voltage across my laptop mouse pad. I tried several sizes of ferrites on various cables
. The small beads, straight through didn't help. I ended up using two large 1/4" ferrites with 3 wraps of cable, close to both ends, on just the serial
cable (from modem to the USB-Serial adapter plugged into the laptop). I did experiment
with other cables
, etc., and reduced it down to just needing the ferrites on the serial cable.
A few other things I've learned. My radio chassis is grounded. However, if the negative DC power cable is long, the manufacturer recommends a shorter ground direct to the boat common bus. My audio cable connects the chassis' ground between the radio and Pactor
II modem. There's no reason to run an additional ground to the modem. I didn't worry about ground on the laptop (at this time). The radio manufacturer also claims that the primary cause of RFI is most likely due to poor grounding on the antenna
tuner. I don't think I need to go there yet, since the radio transmit seems to be working well.
My getting high-voltage shocks across the laptop mouse-pad seems to be resolved at this time. Thanks for all advice above and sorry it took me so long to sort out.