Electronics > RF, Microwave, Ham Radio

Listening at 18kHz with WebSDR

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Circlotron:
Was listening to this site http://websdr.ewi.utwente.nl:8901/m.html with WebSDR iPad app and there are signals as low as 18kHz. Are they likely to be real transmitted signals or just spurious receiver artifacts?

uncle_bob:

--- Quote from: Circlotron on June 12, 2016, 01:00:08 am ---Was listening to this site http://websdr.ewi.utwente.nl:8901/m.html with WebSDR iPad app and there are signals as low as 18kHz. Are they likely to be real transmitted signals or just spurious receiver artifacts?

--- End quote ---

Hi

There are indeed real signals down there. Most of what you pick up is EMI from switching regulators and similar stuff.

Bob

mark03:
VLF comms are really interesting.  One of the US Navy's big transmitters is not far from me here in Seattle:

https://en.wikipedia.org/wiki/Jim_Creek_Naval_Radio_Station

When you're only dealing with the groundwave you can really push the Shannon limit by going low/slow, because the phase coherence of the channel is much greater than at shortwave frequencies.  Here's a fun write-up of an amateur transatlantic communications experiment at 8971 Hz:

http://www.w4dex.com/vlf/8971Hz/index.htm

For a test of the web SDR receiver, see if you can pick up the nearest VLF time-standards stations in the UK (MSF, 60 kHz) or Germany (DCF77, 77.5 kHz).

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