I just purchased a dish finder / pointer ($14 type) and noticed that a lot of them come with a power supply. The power supply consist of two 9 volts and a slip on F-connector. So the question is: How can I make one of those? I'm guessing it's two 9-volts wired in series to make 18 volts and then the F connector is wired with the tip being the positive and the ring being wired with ground/negative?