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To my shame as a radio amateur I must admit I still use a PLC (ethernet over powerline) connection in my home network. It's what makes the shed weather station computer reachable. An upgrade to wifi is in the plans. This evening I played a bit with it and caused heavy traffic on that bit of network using iperf and the results in gqrx are stunning. Around the 20 meter amateur band (14000-14350 kHz) the difference is quite visible. The band itself is clearly notched, but a serious amount of radio noise is visible outside the band. The gqrx displays are the current signal levels across the frequency spectrum in the top half of the display and a waterfall display in the bottom half. The waterfall display shows the history of those levels as indexed colors. The upside: these PLC adapters (devolo) clearly use notching. Interference on amateur bands is small. But I don't receive any other amateur radio signals either so I still have a problem. The downside: outside the amateur bands the interference is quite strong. Weak signals do not survive this. Update 2014-08-17: Sometimes you notice something after a while: the horizontal lines in the 'idle' and 'busy' graphs are very short bursts that sound like ticking when heard on a radio. These are quite probably the way in which the powerline network tests the connectivity and available frequency spectrum including noise levels.