Model BA-2-500 is a 2:1 balun/unun kit used to translate a 50 ohm input to 100 ohms at RF power levels up to 500 watts PEP from 1.8-61 MHz when used with a matched load. The kit comes pre-assembled (already wound and SO-239 connected – just add your own enclosure box) and an instruction manual with directions to connect the kit as a 2 to 1 balun (two port balanced antenna to unbalanced coax input) or 2 to 1 unun (one port unbalanced antenna and one port ground to unbalanced coax input). With a matched 100 ohm load the SWR over the frequency range 1.8 to 61 MHz is shown in the following table measured with an AIM 4170 network analyzer. Notice that the conversion from 100 to 50 ohms is very consistent from 1.8-61 Mhz and SWR is less than 1.6:1 over the range allowing easy tuning by most radio internal antenna tuners or an external tuner. Graph is for a 2:1 balun often used with delta loop, quad or horizontal loop antennas. Kits fit into 4″ x 4″ x 2″ box (Part# CB-Box-1).
2:1 (100:50) Baluns are useful between 50 ohm coax and 100 ohm balanced lines for loops, cubical quads, log periodics and other antennas where the impedance at the end of the feedline is 100 ohms (1/2 wavelength feedline).