Schumann Resonance Converter

Description: Using a circuit similar to the LF block converter, a Schumann Resonance Converter has been developed to shift near-DC signals up to approximately 2 kHz for compatibility with a standard soundcard. The initial test results indicate successful operation, with the irregular lines below 30 Hz representing Schumann Resonance. The accompanying image from Spectrum Lab shows an offset of 2.048 kHz (the local oscillator frequency). A bridged-T notch filter, utilizing a small audio transformer as the inductor, effectively reduces the 60 Hz interference. The inductance of the transformer can be adjusted with minimal current (or a weak magnet), allowing tuning of the filter by dozens of Hz with just 100 µA of DC current.

The circuit schematic begins with an antenna, which should be a long vertical element positioned high above ground, away from obstructions such as trees. The lead-in cable may introduce significant capacitance, potentially up to 1000 pF, which is acceptable. If excessive hum is present for the FET follower, adding a shunt capacitor may be beneficial. Increasing the 220 pF capacitor to around 470 pF could also be considered, though it may affect gain at higher Schumann resonance frequencies.

The first 62 megohm resistor discharges the antenna, while a neon bulb or other gas discharge device limits the voltage, although these components are not depicted in the provided photo. A 0.01 µF capacitor isolates the JFET from voltage spikes and should have a high breakdown voltage. The second pair of 62 megohm resistors biases the JFET gate at half the supply voltage, allowing the source ample swing room due to expected significant AC hum signals. These resistors can consist of three 22 megohm resistors in series. A 10 megohm resistor is included in the signal path, with its noise level remaining below atmospheric noise, working in conjunction with the 220 pF capacitor to limit frequency response above approximately 70 Hz.

A 1 kΩ resistor stabilizes the JFET irrespective of the chosen type. The JFET is lightly biased by a 56 kΩ resistor and some current flowing through the transformer to optimize power consumption for battery operation. The JFET source drives the bridged-T notch filter, with a selected capacitor (denoted as two) resonating the transformer at 60 Hz, determined by the transformer's characteristics (in this instance, approximately 0.11 µF). A 50 kΩ potentiometer adjusts the null depth, which may require experimentation with different transformers.

A 500 kΩ potentiometer and 100 kΩ resistor facilitate current flow through the transformer, enabling inductance tuning for the center frequency. The differential amplifier performs the mixing, with a current sink transistor modulating a small current of about 200 µA, producing a 2-volt square wave at 2 kHz across a 10 kΩ emitter resistor. A potentiometer located on the far right balances the two transistors, ensuring equal duty cycles and canceling the 2 kHz frequency in the output transformer.

The transformers used are compact types with a 10 kΩ to 250 Ω winding ratio, which is not critical. The circuit operates with a low-Q set of values, and exploring telecom transformers with an inductance of approximately 10 H may yield interesting results, although a significantly larger resonating capacitor near 1 µF would be required.

Utilizing the 20 dB microphone boost option within the soundcard settings, a resistor is selected to connect across the output for gain reduction. A shunt resistor across the output serves as an effective means to control gain, ensuring that the time domain display reflects a strong signal without clipping. The total current draw of just 300 µA allows for extended operation on a lantern battery. This battery configuration ensures complete isolation of grounds via the audio output transformer, although a molded supply would also function adequately. The null potentiometer, located on the right in the schematic, can be adjusted to minimize carrier bleed-through at 2048 Hz.Using a similar circuit to the LF block converter, I`ve made a Schumann Resonance Converter that moves the near-DC signals up to around 2 kHz for an ordinary soundcard. Here`s the maiden run plot: It seems to work! The fuzzy lines below 30 Hz are due to the Schumann Resonance. The image is from Spectrum Lab with an offset of 2. 048 kHz (the L. O. f requency). The 60 Hz is reduced by an unusual bridged-T notch filter that uses a little audio transformer as the inductor. I discovered that the inductance of such a transformer can be varied quite a bit with a very tiny current (or even a weak magnet).

Only 100 uA of DC current will tune the filter many 10`s of Hz! Here`s a snapshot of the schematic so far: Circuit Starting on the left, the antenna should be a fairly long vertical mounted high in the air, away from trees. The lead-in cable will have significant capacitance, perhaps as much as 1000 pF, and that`s fine. (In fact, you might want to add a shunt capacitor if the hum is too big for the FET follower. If that`s the case, you might also try increasing the 220 pF capacitor, to, say, 470 pF, but that`s starting to eat into the gain at the higher Schumann resonance frequencies.

) The first 62 megohm bleeds charge off the antenna and the neon bulb or other gas discharge device limits the voltage. Those components are on my RF connector, not in the photo. The. 01 uF helps to isolate the JFET from the voltage and it should have a high breakdown voltage, just in case.

The second pair of 62 megohm resistors bias the JFET gate to V/2, to give the source plenty of room to swing, since there`s likely to be a big AC hum signal. Those big resistors could be comprised of 3, 22 megohms in series. The 10 megohm is in the signal path, but its noise is well below the atmospheric noise, and it works with the 220 pF to roll off the frequency response above about 70 Hz.

The 1k is there to keep the JFET stable, regardless of the type chosen. The FET is very lightly biased by the 56k resistor and some current flowing in the transformer to conserve power for battery operation. The source of the JFET drives the bridged-T notch filter. The selected capacitor (indicated as two) resonates the transformer at 60 Hz, and the value will depend on the transformer; mine was about 0.

11uf). The 50k pot sets the depth of the null and that value may require some experimentation with other transformers. The 500k pot and 100k resistor cause current to flow in the transformer, changing its inductance for tuning the center frequency.

The differential amplifier performs the mixing, with the current sink transistor turning a small current on and off, about 200 uA (there should be a 2 volt square wave at 2 kHz on the 10k emitter resistor). The pot on the far right balances the two transistors so that they are turning on and off with equal duty-cycles, causing the 2 kHz to be canceled in the output transformer.

The two transformers are tiny 10k : 250 ohm (or something like that) types that I have in quantity. The winding ratio isn`t important. It`s a fairly low-Q set of values, and it might be interesting to try one of those telecom transformers that have about 10 H inductance. The required resonating capacitor will be significantly higher, near 1 uF. I`m using the 20 dB microphone boost option in my soundcard menu and I selected a resistor to connect across the output to kill the gain a little.

A shunt resistor across the output is a fine way to control the gain. Set the gain so that the time domain display has a large signal, but isn`t clipping anywhere. The total current drain is only 300 uA, so this can run on a lantern battery for years. Using a battery means the audio output transformer will completely isolate the grounds. It would probably run on a molded supply just fine. The null potentiometer (on the right in the photo) is adjusted to minimize the carrier bleed-through at 2048 Hz. Try adjusting t