Released version 0.3 of my rtl_sdr based spectrum analyzer software for Linux:
xpsa requires a DVB-T USB stick, librtlsdr, libforms (xforms), fftw3, some other stuff.
This one supports any mixers up front (heterodyne), you can set the local oscillator frequency positive or negative for add or subtract.
There is now a small square pad where, if you use mouse buttons or mouse scroll wheel, you can step through the frequencies really fast. If you set 'jump size' to a channel spacing (WiFi for example), then you can just 'roll' through the channels. This last thing assumes my 2.4 GHz to 1.5 GHz mixer in front to course.
The picture shows xpsa looking at the mixer LO.
Code is released under the GPL. These programs are just a snapshot, not very much tested, I add what I need when I need it, If it of use to somebody else great, if you cannot find the clue write a better one. And release the code. For me this has already been very useful indeed.