Thinking is that when coax is coiled, it acts like a balun? To me it was odd that with RG400 requires a minimum length (10 ft) as opposed top RG 58 which has no minimum length. I called Appareo and they told me that corporate memory was lost as to the "why" of ten feet min using RG400. I am just going to go with the instructions and figure out the "why" later ... curiosity more than anything else. (The GPS antenna is mounted just behind the firewall and ahead of the windscreen ... the run to the transponder is about 3 feet) Interesting ... thanks for the reply! R/Lee