High Performance FM Balun built by Ken Wetzel. 300 ohm Balanced - 75 ohm Unbalanced. Low Loss - High CMRR. Weatherproof enclosure. Measures 3 x 2 x 1. I used a large radiator clamp to attach to the antenna. I used this balun with a Radio Shack FM-6 outdoor FM antenna for a few years before I lost the antenna in a wind storm. The measurements on the assembled balun when originally built by Ken Wetzel are: Freq Loss CMRR 88 0.18 47 98 0.19 40108 0.26 38 The loss measurements are accurate to ± 0.4 dB (its really difficult to accurately measure low insertion losses). The CMRR measurements are accurate to ± 2 dB. Common Mode Rejection Ratio (CMRR) determines how well the balun rejects extraneous signals or noise going up the the outside of the coax to the antenna. More than 30 dB guarantees that it will not degrade the antenna pattern. This is useful when trying to reject an undesired signal from the back of the antenna.