Catching Signals in the Very Low Frequency (VLF) Band
Where Radio Meets Science
Discover the Wonders of VLF
The VLF band (3-30kHz, wavelengths between 100 and 10km) is most definitely not where you can witness the sounds of silence, Signals here range from radio astronomy (see previous post) to weather observation and metal detectors (8kHz). There are Navy submarine transmitters in around 50 countries worldwide. You can also find time signal stations (e.g.: Russia: RJH77, RJH63, RJH90; RAB99 [25kHz]; EU: 60 [MSF; USA: WWB], 66.66 [RBU] and 77.5kHz [DCF77]). VLF was also used – in the days before GPS – for navigational purposes. Consider, for instance, the Russian RSDN-20 system (ALPHA) and the NATO counterpart, OMEGA (1967-1997). Even today, you may occasionally resolve sporadic Russian hyperbolic navigational signals on 11905, 12649 and 14881kHz. There are still some LORAN-C signals (100kHz) and some experimental amateur radio signals (sub-9kHz). And this is not all: A lot of geological (land) and bathymetric (oceans) mapping happens in the VLF band, and nuclear detonations can be traced here too. The VLF area is useful for research into the Magnetosphere and Ionosphere, and for tracing meteor emissions, solar activity, eclipses and Coronal Mass Ejections (CME). The list below contains a few examples of the kinds of signals (in kHz) that can be found in the VLF band. Please let me know if you know of any more, and do not forget to check out this website, for some forthcoming reading suggestions on this fascinating part of the radio hobby.
I will take a longer look at how to receive VLF signals in the December issue of RadioUser. Meanwhile, the pictures show some of the equipment I am using, in conjunction with my PC, a 192kHz soundcard and the Spectrum Lab software suite.