Dull saw, PVC, hot glue, extra junk = common-mode clamp for finding RFI sources. Seems fairly flat across 50khz to 10MHz (somehow) and added an old 5v plug so i can stick in a 1uF capacitor and see down to 1khz. It rolls off up higher but even the 100mhz fm broadcast signals on my coax shield come thru fairly strong. Now i can go around the house with the laptop and a bag of ferrites