Re: Strange VLF signals


D R
 

Hi Allan,

Sunrise here today was at 0743, and the 16kHz signals started at 074622.  I'm guessing that the panels need to be producing DC above a certain threshold before the controller switches the inverters on, but the correlation between the signals and sunrise/sunset is already pretty clear.  I'll do another recording this evening to catch the signals turning off.  I can download data from the controller which tells me what the panels and inverters are doing, but only at five minute intervals, so I won't immediately be able to find an exact match for their status and the 16kHz signals on/off times - but near enough will be good enough, I think.

The microinverters are Enphase M215 units, but the datasheet for them doesn't disclose much.  However, you can see from the attached screenshot that the carriers appear to be pulsed at different frequencies (4Hz for the inner ones), which is probably to do with synchronising the outputs from the 16 inverters into a coherent supply which can be backfed into the Grid.  As you say, the signals appear to be crystal controlled, so microprocessor noise is quite feasible.  I assume the signals you see also disappear around sunset?  I can also see weak groups at 16kHz intervals up to 80kHz, so I think we are both picking up the same thing.  I've also got a very strong group at 68.94kHz which I'll need to check after sunset to see if it's solar panel related as well.

Regards,
Dave

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