Receiving VLF with an Upconverter and Direct Sampling RTL-SDR

Recently amateur radio hobbyist DE8MSH wrote in to let us know about how he was able to receive VLF (Very Low Frequency) signals using a very rare Refcom FC-VLF upconverter and his direct sampling modified RTL-SDR.

His antenna is the PA0RDT mini whip which requires 12v of power that is delivered directly by the Refcom FC-VLF. He writes that the Refcom upconverter is used to upconvert the 9 to 50 kHz range into the 14.009 to 14.050 MHz range which is receivable by a direct sampling modified RTL-SDR. Using this set up he was able to receive several VLF stations as shown on the waterfall image below.

15 - 70 kHz VLF Received with an Upconverter and Direct Sampling RTL-SDR
15 – 70 kHz VLF Received with an Upconverter and Direct Sampling RTL-SDR

DE8MSH also writes

Note that I’m not living in a quiet area. As you can see there is a lot of men made noise like from tv sets, lights bulbs etc. pp. Some signals are not very strong becaus I switched the Refcom to 9-50kHz filter. So some stations above 50kHz could be stronger.

Below are some close up shots of VLF signals being received.

17 to 27 kHz
17 to 27 kHz
37 to 47 kHz
37 to 47 kHz
47 to 57 kHz
47 to 57 kHz
67 to 77 kHz
67 to 77 kHz
77 to 87 kHz
77 to 87 kHz

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