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).
RFI/EMI Solutions from KHz to GHz
Now you can get a ferrite snap on combo pack of 10 RFI filters in 1/4" size with all three filter ranges (great if you don't know the interfering frequency and need to cover the entire range when troubleshooting an RFI problem).
Mix 75 covers 150 KHz to 10 MHz (3 filters)
Mix 31 covers 1-300 MHz (usable to 500 MHz) (4 filters)
Mix 61 covers 200-2000 MHz (3 filters)