When I try to transmit, my 447HPC2 displays E4 and won't key. Shawn November 11, 2016 22:43 You have a high SWR. E4 means SWR protection mode stopped the radio from transmitting to avoid damaging your radio. Related articles How do I calibrate the SWR meter on my radio? Radio Displays E2 Error Code How do I turn the SWR Meter on? SR-447HPC2 Setup Guide SR-447HPC2 Manual Comments 0 comments Article is closed for comments.