Construction of an ELF receiver: amplifier and filters
After the antenna comes the analog front-end — a chain that amplifies the weak signal and shapes it in frequency before digitization. In the portable receiver described in [Votis2018], this chain achieves a gain of approximately 112 dB at 10 Hz, with an equivalent input noise of only about 2.88 nV/√Hz.
After the antenna comes the analog front-end — a chain that amplifies the weak signal and shapes it in frequency before digitization. In the portable receiver described in Votis 2018, this chain achieves a gain of approximately 112 dB at 10 Hz, with an equivalent input noise of only about 2.88 nV/√Hz. Such low noise is essential, because the useful SR signal has amplitudes on the order of nanovolts to microvolts.
A key part is the filters. A bandpass filter delimits the ELF band of interest (a few to tens of Hz), while narrowband notch filters suppress the dominant interference of the power grid at 50 Hz (or 60 Hz) and its harmonics (see #38). A low-frequency limit in turn suppresses very slow drifts and the DC component.
Low intrinsic noise of the amplifiers and a stable power supply are also important. Thanks to careful design of the front-end, clean peaks of the first six SR modes are resolvable in the measured spectrum already with an acquisition of around 10 minutes Votis 2018.
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Sources
- Tatsis2024Tatsis, G., et al. (2024). Instrumentation and Measurements of Magnetic Coil Schumann Resonance Receivers. IEEE Instrumentation & Measurement Magazine.Open source
- Votis2018Votis, C., et al. (2018). A new portable ELF Schumann resonance receiver: design and detailed analysis of the antenna and the analog front-end. EURASIP J. Wireless Commun. Netw.Open source