I have built a "slim-jim" folded wire antenna for 160.7 MHz (approximate center of the railroad frequency band) for my Uniden BC92XLT scanner from 300 ohm ladder line, modifying a 2-meter design from the Internet. I used the W7AY cocoaNEC2 antenna simulator program (see www.w7ay.net) to optimize the design and achieve a theoretical 50 ohm feed point impedance at 160.7 MHz, but I have no way to confirm the antenna impedance. The antenna seems to be working well, but my question is: Exactly what scanner input impedance should I be trying to match to the antenna? The BC92XLT spec lists a nominal 50 ohm input, but how much does Zin vary with frequency? RF transistor data sheets show input conductance will vary considerably with frequency. Have the scanner designers managed to flatten the Zin. vs. Frequency curve, or is the input impedance at 160.7 MHz likely to be significantly different from the published 50 ohms. How do you determine Zin of a scanner at a specific frequency?