A Piper PA-32R aircraft equipped with a GNS-430W was reporting loss of GPS fix when the VHF comm was in use on certain frequencies. The VHF antenna is on the bottom of the fuselage, and the GPS antennas are located on the top. It was determined that the frequencies this occurred on were were between 121.0 and 122.0 MHz. This is nowhere near GPS frequencies, which are at 1.57 and 1.23 GHz. So what causes a complete loss of fix when the VHF transmits? The ELT (emergency location transponder) transmits at 121.5MHz. The ELT is off in flight and only activated when an aircraft crashes, or manually by a pilot in distress. The VHF comm transmissions *near* 121.5 energized the ELT's transmitter, which had a wire running very near the GPS antenna wires. The resultant interference on the GPS antenna wires caused the avionics to lose the fix. For a pilot shooting a GPS/WAAS approach in IMC, activating the comm would cause GPS failure, and force the pilot to execute a missed approach. Ultimately, this could make safely landing the aircraft at an airport impossible.