To figure out the true freq, you must know the 2nd IF, which is 21.400 mhz. its in the spec. section of manual than you multiply x 2 which gives you the 42.800 mhz. So if your finding something out of band give this a try, It's either up or down 42.800 mhz. Like i was finding channel 2 tv reporters on 407.4875 i know there not suppose to be there so i found the 2nd IF than multiplied x 2 and it put me on 450.2875 mhz. right where there suppose to be. Happy Monitoring