Okay, I was not reading carefully enough: it is a Xantech system.
Or have you tried putting ferrite beads on the neon transformer's power cord? Have you called a sign company to see if they know of any methods to reduce EMI put out by their products?
A good answer is easier with a clear question giving the make and model of everything. "The biggest problem in communication is the illusion that it has taken place." -- G. “Bernie” Shaw
