The RTLSDR dongle came just before a weekend, meaning I could spare half and hour playing with it. The first kitchen table test with the stock antenna showed that it could receive local beacons in 2m, 70cm and 23cm (in line-of-sight). When I moved to the shack on the other side of the building, beacons were hidden and the DVB-T antenna was not enough anymore.
So I quickly cut a 23cm dipole and soldered it to the end of a short TV cable. With this antenna moved inside the shack room the local beacon became visible and audible again. But there was also another signal up there!
At 1297.000 MHz local HAMs were testing a new repeater. In the SDR# screenshot above you can see an FM QSO, with "Operator 2" having a very narroband signal: with a couple of clicks I fixed his S/N and his voice was loud and clear.
I sent the screenshot to the repeater designer and I got a positive feedback about this SDR setup. I also used the repeater frequency to insert the needed frequency correction into the software (+61 ppm in my case), otherwise frequencies don't match.
Having worked for users of microwave transverters, which once upon the HAM time had troubles locating their respective signals over the wide RF spectrum sea, an SDR application like this would greatly simplify "meeting" for a microwave QSO!
When is the next 23cm contest?! (tomorrow!)