yes i recognise this signal well, kinda odd I get them in random places like up near the ATC above broudcast FM - http://i.imgur.com/SXkX7Gd.jpg

My dongle is on an extension cord hanging away from my computer, but it is near a 12v to USB power adaptor I use to charge my phone and this is what happens when i turn that off the signals just vanish, along with a lot of other noise.

So i sit there for a while and let it all relax and after there's been no sign of the noise in ages i turn the usb charger circuit back on and you can see as it warms up the noise starts up again

So without a doubt it's the usb charger making the noise, this thing the back box with two wires coming from it, a tiny switched mode DC-to-DC converter - the radio is the dongle held in place by my trusty lion, and in the other picture you can see where the usb charger get's it's power from that's just a simple splitter box from a solar charge-controller outside.

also interesting to note, when unplugged the real signals and noise vanish - that's the dark blot at the bottom, towards the top I turn off my usb again and that vanished but we can still see a faint and wider signal, that's could be my laptop which i recently turned on or some local noise like an oven or powertool.. Waving my laptop at it doesn't affect the signal so it's likely we can rule that out, if i ever manage to get my stupid windows laptop to accept the dongle then i'll be able to go to the park and sit there and if the signals are still visible then that rules out very local noise, i could then go into town and if the same noise is there is rules out village noise....

This is my dongle moved to the other other side of the room into a different antenna, here you can see the blue gap where i unplugged, the fade in signal just before is me moving it to get at the antenna socket, not much difference locally after the initial fall off - then i turn it off and we see no change in the wider noise signals again, so we can't move it away from the noise source in my shed but there is a way to work out what it is....

[this]() explosion of noise is what happens when i move my dongle and antenna towards the other biggest electrical device in my shed, the computer... Then i move it away slowly and you can see a small drop-off, i got to about two meters before knocking the connector [the blue bump] at which point i put it about three and a half meters away which is the furthest point..

If i ever get my darned laptop to work then i'll be able to turn my base unit off and see if the noise persists.