23 Jan 2021 "A new portable ELF SR receiver"- 4: Signal Conditioning Chain.
14"A new portable ELF Schumann resonance receiver", by Constantinos Votis; Part 4 -- Signal Conditioning Chain
*****
(PART 4 -- Signal Conditioning Chain )
Analog front-end, regardless of its architecture, carries out filtering and amplification of received signals to the level required for the data acquisition module [28].
Specifically in this work, the filtering and amplification setup consists of six cascading circuits which provide amplification and filtering of the induced very low-amplitude voltage signal (few tens of nV) coming out of the coil.
Figure 3 shows a block diagram of the electronic chain.
Our filtering and amplification chain consists of the following stages: preamplifier, low-pass filter and notch filter, double notch filter, double low-pass filter, high-pass filter, and variable gain amplifier.
Since the maximum current of the signal condition setup does not exceed 120 mA, one 47-Ah battery with a 2.5-W solar battery charger extends autonomy for more than 45 days.
Data acquisition and processing system has already been presented by Tatsis et.al [29] for the purpose of digitizing signals of the entire ELF band, with 16-bit resolution and an adjustable sampling rate.
[FIGURE 3 -- Filtering And Amplification Chain]
For better noise performance and less signal degradation and distortion, the preamplifier was mounted directly on the coil inside the Plexiglas container as shown in Fig. 2.
Preamplifier
The first stage of the signal conditioning setup, which is the preamplifier, is shown in Fig. 4.
The preamplifier stage is based on a non-inverted operational amplifier topology.
The RC circuits at both VCC and VEE were used for decoupling purposes at both positive and negative supply voltages.
Similar RC decoupling circuits were used in every stage of our filtering and amplification chain.
The preamplifier’s gain was equal to 35.5, and the − 3-dB cutoff frequency due to the RC filter in the output is 0.24 Hz.
In order to achieve additional low-noise performance, the OPA209 operational IC amplifier was chosen because it exhibits very good low-noise performance.
For further investigation, we designed and implemented two more preamplifier stages that are based on inverted operational amplifier architecture and instrumentation amplifier topology, respectively.
Taking into account our antenna coil architecture, we provided both simulated and measured results.
These results indicated that both of those two alternative preamplifier stages had limited performance.
[FIGURE 4 -- Preamplifier]
[...]
** **
Complete description, Wordpress link: (https://vertearbustosschumannresonanceharmonics.wordpress.com/24-jan-2021-observations-what-are-schumann-resonancesbasic-introduction-to-a-schumann-resonances-detector-antenna/)