There is no technical help with the projects. This circuit is shown as an educational example only.

This is a very fun circuit to play around with and it will cause a meter to move in response to ELF magnetic fields in the range of 0.5 Hz to 30 Hz.

Power this from a 9-volt battery.

Meter will wiggle at the received frequency. Try spinning a magnet on the floor 5 feet away and watch the meter!

Use this circuit to detect magnetic storms in Earth's magnetic field, or mount a magnet on a weight to make a seismograph pickup unit, or mount a magnet on a piece of rubber stretched across a large sealed drum to make an subsonic microphone for "listening" to 1 Hz - 30 Hz.

PARTS:

There is no technical help with the projects. This circuit is shown as an educational example only.

Q1, Q2, Q3, Q4, Q5: STORMWISE PART # 2N4124 NPN Transistors.

ELF Antenna: Select one of our SLF or ELF antennas for best results.

C1: 470 pF capacitor.

C2: 47 uF capacitor.

C3: 0.22 uF capacitor.

C4: 22 uF capacitor.

C5: 0.1 uF capacitor.

C6: 0.47 uF capacitor.

C7: 1000 uF capacitor.

R1: 1000 ohms resistor.

R2: 47 K-ohms resistor.

R3: 47 K-ohms resistor.

R4: 2 Meg-ohms resistor.

R5: 200 K-ohms resistor.

R6: 20 Meg-ohms resistor. (use two 10 megs in series).

R7: 4.7 K-ohms resistor.

R8: 2.2 K-ohms resistor.

R9: 15 K-ohms resistor. May need to adjust depending on METER used.

VR1: 10 K-ohm variable resistor. May need to adjust depending METER used.

METER: 0 - 30 uA (microamps) analog meter.

SW1: Any pushbutton SPST switch for "ON/OFF".

Operation:

There is no technical help with the projects. This circuit is shown as an educational example only.

IMPORTANT!: When first turned "ON" allow up to 1 minute for the capacitors to fully charge up before the circuit starts working. The circuit may appear to do nothing for up to 1 minute while the capacitors charge up. The meter may swing back-and-forth once or twice before settling down at the center reading.

This circuit is a wideband unit that will pickup 0.5 Hz to 30 Hz. Modifications can be made (see below) for resonance going below 1 Hz).

Apply power without any antenna connected.

Adjust VR1 until 30 uA meter reads center scale (15 uA). Assuming circuit is powered at 9 volts.

Connect the Antenna.

Moving a magnet near the antenna will cause meter to move.

Moving the antenna will cause meter to move, as the antenna moves in Earth's magnetic field.

Keep antenna away from TV's and CRT screens, power transformers, etc that might introduce 60 Hz into the circuit.

The circuit is sensitive from 0.5 Hz to 30 Hz. The Q1 and Q2 transistors have the high-frequency bypass capacitors (C3 and C5) which prevent overload by frequencies higher than 60 Hz.

There is no technical help with the projects. This circuit is shown as an educational example only.

Note that the meter will wiggle slightly and randomly below 0.5 Hz (due to "thermal flicker noise" or 1/F noise) when no antenna is connected. It will also move in the same way when the antenna is connected (and yet no signal is being received). Become familiar with how it operates so you don't confuse slight thermal flicker noise as real magnetic signals.

Note that touching Q1 or Q2 with your finger will cause the meter to deflect full scale due to heat transfered from your finger to the transistor. This circuit is -that- sensitive to small input current changes in the transistors! Keep the circuit's temperature environment stable.

Because this circuit is so sensitive, power this from a 9-volt battery. KEEP the circuit away from drafty areas where temperature changes rapidly.

You can change C2 to 220 uF and C4 to 100 uF and C6 to 1 uF to get some very slow resonant frequencies below 0.5 Hz. Allow some time for meter to stop swinging at less than 1 Hz, it may look like slow feedback oscillation, but it is not. You will see a slow decay time at these extremely low frequencies below 1 Hz.

There is no technical help with the projects. This circuit is shown as an educational example only.

Antenna exibitd a bi-directional reception pattern as shown above.

Looking down from above with the ends of the antenna pointing North and South, just like a compass would, the directions of best reception are EAST and WEST as shown by the circles in the chart above. There is no signal pickup from the North or South. To pickup from the North and South you would have to point the ends of your antenna to the East and West.

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