AVT3054 / 5 A

MULTIODORNIK ELF-VLF - FILTER MODULE - PRINTED PLATE

Producer: AVT

The ELF-VLF receiver, or rather a set of receivers, enables reception of mysterious radio signals with extremely low frequencies. It is possible to observe signals of communication with submarines and so-called Schumann resonance.
It is possible only in extra-urban conditions (eg during trips), and this is due to the high level of industrial disturbance in cities. In the city, the described systems can be used, for example, to observe storms and the level of industrial disturbances. Such their use can also be very interesting. A lot of information about the reception of electromagnetic waves at very low frequencies, below 30kHz, as well as about antennas used for this type of receivers, is provided in the article 'Receiving ELF-VLF radio waves'.
The project presents four receivers, designed to receive radio signals (electromagnetic waves) in the range from 3Hz to 30kHz, thus including bands: ELF, SLF, ULF and VLF. The first of the receivers (I) cooperates with a wire antenna, reacting to the electrical component of the electromagnetic field. It was made in two system versions (Ia and Ib). The third and fourth are designed to cooperate with a loop antenna, reacting to the magnetic component of the electromagnetic field. The article also describes the system generating symmetrical power supply voltage and systems improving work comfort by increasing resistance to unwanted signals: two low-pass filters with band respectively 200Hz and 20kHz, bandpass filter, reducing the hum of 50Hz and optoisolator m signals .cz. The described systems do not require tuning or startup, so that even a novice electronics can do it. The big advantage of these systems is the low cost of their implementation.

Note: the project has been divided into 6 parts:

• AVT3054 / 1 - Receiver designed for cooperation with an electric antenna (version Ia and Ib)
• AVT3054 / 2 - Receiver cooperating with a magnetic antenna I
• AVT3054 / 3 - Receiver cooperating with magnetic antenna II
• AVT3054 / 4 - Power supply symmetrization
• AVT3054 / 5 - Filter module
• AVT3054 / 6 - Optoisolation of audio signals

AVT3054 / 5
The task of low-pass filters is to limit the bandwidth of the received signal, which is then processed by the sound card of the computer. However, the task of the notch filter (i.e. a very narrow bandpass filter) is the elimination of 50Hz signals. 50Hz signal, i.e. mains noise is the strongest signal that occurs during ELF spectrum observation. And most often it is its high level that effectively limits the ability to observe weak signals in this band. These filter systems have been designed using the popular integrated circuit TL074, containing four low-noise operational amplifiers in one housing.

Includes AVT3054 / 5 printed circuit board and documentation.

Detailed description in EdW3 / 13 or

Additional materials:

Article 'ELF-VLF radio reception' from the journal Elektronika Dla Wszystkich 10/2011