I'm building an ultrasonic arc detector for locating power pole RFI. It's mostly per the design by W1TRC in the April 2006 QST, plus some additional notes by N0SS. I found a 12" aluminum parabolic dish for an acceptable price so I'm using it rather than the much more costly 18" size of the original. The dish will have a wider half-power beam width and a little less gain but should still be quite usable. The calculated beam width is about 1.75 degrees which is 11 inches at 30 feet. Today I got the transducer well mounted at the focal point and am using a camera tripod to hold the dish for testing. I set up an ultrasonic transmit transducer about 30 feet away driven with a signal generator to check alignment and beam width. The very strong received signal can be observed directly on a scope. The next phase is attaching a handle and providing a simple aiming sight, then on to the circuit construction.