Performance of the End Fed Half Wave antenna (EFHW) which I bought recently has not been good on 40 m, due to compromised mounting as a result of space constraints at home. My friends advised me to try adding a 1:1 balun in addition to the regular 49:1 balun at the feedpoint, to avoid the unbalanced current on the outer surface of the coaxial cable shield, also known as common mode current. As I did not have a regular 1:1 current balun at hand, I thought of adding an air core balun made out of surplus part of the feedline itself. Looked around for a three inch PVC pipe and found none in the store. It was then that the nice PET bottle in the kitchen table attracted my attention. It was exactly three inch in diameter. Started working on it after documenting the initial VSWR on 40, 20, 15 and 10 m amateur radio bands.
