great and useful app. many thanks

There is a slight problem with it. frequency signal reception differs from radio to radio. eg I get no signal from N900 on 93.0 fm but I get signal on an ericsson phone at 93.0 fm. since the empty signal should be on the receiving radio and not the transmitting (n900) it's a bit of a problem here.
I have scanned the all frequencies and I found 7 empty with e.f.f. on another radio these frequencies were not "completely" empty. only one of them had a little hissing noise.
I don't know what will happen with my car radio as I have not yet tested it and I am sure it has a very good reception.