For months, I've been trying to chase down the source of some RFI getting into the HF rig when I was running anything over about 500 watts into my 6m Yagi, which is only about 10 feet off my roof. The hard part was that while it happened more often than not, it was still intermittent. It also only happened using 6m SSB, not the digital modes. I unhooked everything plugged into the Elecraft K4D - USB cables, the mic, other antennas; I even wound the power input on both the amp and rig with ferrite and couldn't find the source. The RFI feeding back into the rig was so bad that just transmitting with dead air on SSB caused horrible signal distortion, making me unintelligible.
After months of banging my head, I finally figured it out. The RFI was coming in through a set of older Sony earbuds that I used to monitor myself while transmitting. As chance would have it, I never monitored my TX using any other mode than SSB. Since I always used these while trying to chase down the source, it was usually present. Then one day I unplugged them and just monitored through the speakers and there was no RFI distortion on TX. I plugged them back in and it was back. After cursing a few times, I swapped them out for a newer set of headphones with a shielded cable, and the problem was still gone. RFI feeding back into the rig through the unshielded headphone cable was the problem the whole time, and it only took months of troubleshooting to figure it out!
After months of banging my head, I finally figured it out. The RFI was coming in through a set of older Sony earbuds that I used to monitor myself while transmitting. As chance would have it, I never monitored my TX using any other mode than SSB. Since I always used these while trying to chase down the source, it was usually present. Then one day I unplugged them and just monitored through the speakers and there was no RFI distortion on TX. I plugged them back in and it was back. After cursing a few times, I swapped them out for a newer set of headphones with a shielded cable, and the problem was still gone. RFI feeding back into the rig through the unshielded headphone cable was the problem the whole time, and it only took months of troubleshooting to figure it out!
