1/4 Wave GP and Balums

Facts First 

 1 ) Coax is " unbalanced ".   In a perfect system RF flow along the outer part of the inner conductor and the inside of the shield.  

2) A dipole is a " balanced antenna " 

3) A 1/4 GP is an " unbalanced antenna " 

4) To prevent the transmission line from becoming a radiator  ( currents on the outside of the outer shield )  a balum should be used.  

5) Balums are required when going from an unbalanced transmission line to a balanced load ( antenna ) .  

6) A Balum ( RF Choke ) is nothing more then a high impedance  device to force currents to flow through the lower impedance load ( antenna ) 

I was amazed at the 30m,  40m and 17m ground mounted 1/4 vertical antennas that I recently built.   They match easy VSWRs all below 1.1 : 1 at the tuned frequency.     I didn't realize at the time why these antennas worked out so well but the whole unbalanced to unbalanced thing makes sense.  

Came across this cool little video that explains it rather well ....