2013-03-18 Continuing the search for the source of ...
Continuing the search for the source of the interference on 2 meter amateur bands. This evening I tried disabling the powerline network completely, unplugging both ends of the link. First I made a 'baseline' fft graph with gnuradio of the 2 meter band and then I disabled the powerline network and tried to make the same graph. Which failed completely: the dab stick I use for software defined radio has some automatic gain control which made comparing baselines difficult, the graphs had a jump in signal level of more than 20 dB. But I left that run of gnuradio with the fft graph running and switched the powerline network on again. Those two graphs are somewhat easier to compare: the peak signal level on 144.800 (aprs frequency) is nearly the same. The base noise level on the band indeed goes up about 1-2 dB.
Listening with a receiver earlier I did notice the noise starts to actually have rattling sounds and high tones in the back yard. Time for more research there. I should compare the results with receiving and interference on a receiver with powerline networking enabled and disabled, but I didn't find time to do that with all the running around to change the powerline network. This is what I like in amateur radio: researching how something works or doesn't work and why. Update 2013-03-19: Some walking around and some testing again: the linksys WAP54G indeed does cause some noise. And the most likely source of the noise in the back yard is the automatic light switch! The heater we have is a Vaillant with OpenTherm support, but it does not cause interference.
- fft-plot-gnuradio-2m-plc-disabled.png gnuradio fft plot with the powerline network disabled
- fft-plot-gnuradio-2m-plc-reactivated.png gnuradio fft plot left running with the powerline network enabled again