Put an Opto Isolator where the Icom connects your Icom CI-V serial network bus.
That simple 2-wire system can easily act as an antenna (just like stereo speaker wires)
for stray RF or Common-mode RF issues from your antenna, that you have not addressed.
DF4OR - Primer on the Icom CI-V serial (network) bus http://www.plicht.de/ekki/civ/
CIV / CI 5-Communications Interface-V Reference Manualhttp://www.icomamerica.com/en/support/kb/article.aspx?ArticleNumber=63AE624429
Greg Ordy, W8WWV - Yet Another ICOM CI-V Interfacehttp://www.seed-solutions.com/gregordy/Amateur%20Radio/Experimentation/CIVInterface.htm
The Icom CI-V serial bus was conceived, designed, and first offered in the early 1980s.
For that time, it was state of art for an inexpensive amateur radio solution,
BUT as K9JM discusses below -- they had no method for message management (collisions).
James A Michener, K9JM
ICOM CI-V Router -- using Arduinohttp://www.k9jm.com/CIV_Router/CI-V%20Router.htmlBring new technology to a legacy bus.http://www.k9jm.com/CIV_Router/Riding%20the%20CI-V%20Bus.pdf