Due to its electrical nature, this type of antenna collects a lot of noise. The random wire antenna is a type of antenna consisting of a cable suspended above the ground, whose length is not related to the desired wavelength but adapted according to the available space. The wire must be insulated with a plastic cover, or an enameled wire can be used. An Earth dipole (to listen to the interior of the earth).For the antenna, there are at least three solutions to follow (see Figure 3), according to the difficulty of the work to be performed, the results to be obtained, and the space available in the house: In theory, given the low frequencies used and the related enormous wavelengths, an antenna with gigantic dimensions would be needed, even hundreds and thousands of kilometers. The antenna is the main element in any radio station, transmitter or receiver. For initial tests, the preamp and filter can be omitted.įigure 2: A typical low-cost listening station that anyone can do There are programs (even in freeware version) of excellent quality that also perform the function of amplifier and filter. Note that most of the work is done by the software. An electrically quiet and peaceful place.As shown in Figure 2, the main components to be used are the following: It is possible, for example, to store audio material on CD-ROM or DVD for long-term archiving.Īs mentioned above, building your own listening station in the VLF band is very simple. After gaining some experience, it is useful to create a rich database of received signals in WAV format, also marking the date and radio frequency in which the recording took place. Precisely for this reason, it is useful to carry out studies in the open countryside, far from the inhabited center, where the electrical disturbances are of lesser intensity. Unfortunately, the main frequency (50 Hz or 60 Hz) is very present in the spectrograms and often constitutes a small obstacle to overcome, due to the interference produced and the noises generated. In it, there are natural signals of any kind, both external and internal, generated by the earth and impulses also transmitted by human stations of various kinds. The 0- to 22-KHz band is still a mysterious and not enough explored field. The latter are always coded and digital, so their interpretation is often complicated. In a spectrogram at these frequencies, all kinds of natural and human signals can be observed.
#Vlf receiver circuit listen to meteor software#
It is sufficient to have a personal computer equipped with a sound card and software to obtain an analysis of the observed band. Today, it is very easy to receive low-frequency radio signals and it is not necessary to have an expensive receiver. A different coloration or intensity of the graph (Z-axis) describes its power.įigure 1: A typical monochromatic spectrogram in the 0- to 24-kHz band As it can be seen from the time domain recording, the X-axis represents the elapsed seconds and the Y-axis represents the frequency in which the signal is recorded. A software or hardware that analyzes the spectrum works our ears and is the primary means for analyzing and recording signals in this band. On the contrary, the various emissions “listen” by decoding and appropriately interpreting a spectrogram (see Figure 1). In these low-frequency bands, the signals are not heard in loudspeakers or headphones, or rather, the emission of sounds could occur but it is not the main activity, as is normally the case on other frequencies. Animals and humans are probably also able to receive some signals of this type and our brains may be more sensitive to the ULF band. It certainly gives a lot of satisfaction, even using low-cost emergency vehicles. The VLF band is a very small fraction of the entire radio spectrum. In addition to the sound card, a software is required for viewing, recording, and analyzing the received signal. Our computer’s sound card behaves like a great receiver but must be connected to a suitable antenna. On these low frequencies, there are no satisfactory receivers on the market and the antennas must be prepared with great care. For example, a half-wave dipole tuned to a frequency of 1,500 Hz should have a range of about 50 km. If the generation of a signal at these frequencies is very simple, it is not so easy to build the tuned antennas, as the corresponding wavelength is equal to hundreds and thousands of kilometers. As it can be seen from the table below, these are very low frequencies, corresponding to the audio frequencies that can be heard by humans, but which also involve emissions of electromagnetic waves. The band we are going to “listen to” is located in the frequency between 0 and 22 kHz.