I was just looking at the spectrum here I could pick up from 2 to 1000 MHz. I'm using a ham antenna that is designed for 144 and 440 MHz, so take that into account. Lot's of signals here in the DFW metroplex (TX, USA).
On the left of course we have the strongest signals in the FM broadcast band, among others. Then a large gap from about 220 to 470 MHz. At 470 we start more TV channels and then go to various services such as police and so on, and the cell phone bands. I'm interested in the large gap where not much is happening. I need to pull up a spectrum chart and see what is assigned there.
Anyone else want to do the same scan from another part of the USA or another country? Use whatever antenna you can and we'll realize it's not optimized for all the frequencies.