Useful constant signals at both ends of the UHF airband would be these, though an SDR might be needed to compare signal strengths:
* DAB (numerous sites show the channels used)
* Airwave TETRA (390-395)
* USAF P25 control channels from Lakenheath (410.425, 411.675, 413.375)
and Mildenhall (414.15)
There is only one control channel at each site, and it transmits permanently, though the frequency changes now and again under circumstances that are not entirely clear.
* VOR Coltishall CSL TACAN 116.5 and Wattisham WTM TACAN 109.0 - both relatively low power though.
* Paging signals at 137/138 Mhz. (137.975, 138.025, 138.075, 138.15, 138.175)
I reserve the right to ignore people who have made no attempt to the read the manual, and expect others to do it for them.