Though some VLF stations have other purposes, the primary function of most VLF stations is to communicate with submerged military submarines or help them navigate underwater. They penetrate deep into the earth and deep into the sea (especially in the lower portion of the VLF spectrum) and therefore can be received by submerged submarines. Signals from powerful VLF stations can be received worldwide. The guide below is provided to assist them in identifying stations they receive. However, because VLF receivers and receiving antennas are easy to construct, the VLF spectrum attracts a small number of curious and sometimes very dedicated VLF listeners who want to learn more about this little-known and somewhat secretive part of the radio spectrum. Because of that, few Radio Amateurs or shortwave listeners have ever heard VLF signals and most know very little about the large number of stations in that part of the spectrum, what those stations are used for, or the nature of VLF radio signal propagation. Furthermore, most antennas used with standard communications receivers are optimized for higher frequencies and perform poorly in the VLF spectrum. Standard communications receivers do not receive signals that low in frequency. T he Very Low Frequency (VLF) radio spectrum extends from 3 to 30 kHz. Very Low Frequency (VLF) Stations The S-Meter site continuously receives 24.8 kHz signals from NLK in Jim Creek, Washington, to detect real-time Sudden Ionospheric Disturbances (SID's).
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