To my shame as a radio amateur I must ad ... / 2013-11-20

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.

gqrx receiving radio signal around the 20 meter amateur band with the PLC network idle.

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.

gqrx receiving radio signal around the 20 meter band with the PLC network loaded with heavy traffic

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.