This is constructed as shown using coaxial cable. It is important to use good low loss cable, especially if you use high power, even 0.2db of loss at 500 Watts would be 22.5 Watts dissipated in the balun!
As can be seen in the diagram the, l/2is an exact electrical half-wavelength so the velocity factor of the coaxial cable used for the loop has to be used in the calculations. The outer braids of the three ends are connected together; two of the inner conductors (one of the loop, and the down lead) are connected to one radiator and the other end of the loop to the other half of the radiating element. This is another time when the MFJ antenna analyser comes in handy.
Again make sure the connections and the ends of the balun are well weatherproofed.
This type of balun can be used on folded dipoles, delta matched and 'T' matched antenna systems where an impedance
change from about 200 ohms to 50 ohms is required.
This Page is © 
1999