Today I was working 20 meters in the morning on my home brew dipole. The balun is also homebrew This afternoon it seemed like the band was dead. I checked the SWR and it was 4:1. I couldn't believe it, what happened? I went outside and disconnected the pl259, screwed on a short jumper and had almost a perfect 1:1 across the band with the analizer. The highest reading was 1:5. Back in the shack I checked the coax with analyzer and checked distance to vault. It read the distance to the end of the line. Back outside and looked at the pl259 on the end of the coax. Very slight green discolor. Got some steel wool, cleaned everything up, coated everything with dielectric and resealed. Back in shack all is good. The point is I can't believe how fast I went from almost a perfect match to 4:1. I thought a problem like that would take time to develop. I had been working DX with no problem in the morning. The weather has warmed up which may have caused some expansion.