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

VLF Whistler Receiver

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

Radio Shack stores have most of the parts. The circuit was designed to use a Stormwise portable antenna having very high output impedance: This is any of our antenna part numbers starting with "C" or "AF".

fet preamp

This simple one transistor receiver allows you to listen to VLF and ULF radio waves. It produces enough volume to drive a crystal earphone or a piezo speaker or a piezo buzzer. The 1 transistor receiver produces enough output to drive the "line level" audio input of audio recording equipment, and way too much volume when connected to a microphone input having a 1 millivolt (mV) sensitivity.

Add a second transistor for driving a standard speaker or standard earphone. See this added 2 transistor project lower on this page.

There is no diode AM detector stage in this receiver because the frequencies received are already in the audio range. The receiver converts the magnetic field part of the radio wave into sound you can hear.

Hear tweeks, whistlers, dawn chorus, hiss, and other natural radio wave emissions in the range of 100 Hz to 20 KHz with this receiver. Most of the emissions are below 10 KHz.

Whistlers are found in the range of 1 KHz to 4 KHz, Tweeks are in the range of 1.7 KHz to 2.5 KHz, Dawn Chorus is in the range of 800 Hz to 1.2 KHz, Hiss is in the range of 100 Hz to 5 KHz.

Lightning flashes cover the entire VLF range and long distance reception is peaked at around 10 KHz.

The JFET transistor operates similar to a vacuum tube but it works with 9-volts instead of 150 volts which makes it safe to experiment with. A JFET has very low noise generation in comparison to a standard transistor. A JFET has a very high input resistance, this simply means it is very sensitive to electrical voltage. The STORMWISE antenna generates an electrical voltage which is a perfect input match for this type of transistor.

The input impedance of this receiver is 1,0000,000 ohms (1 million ohms ) which is set by R1. Removing R1 will make the receiver ring at the antenna's center frequency, sound will not be as pleasant, but sensitivity will be outstanding. Lowering the value to 500000 ohms will further widen the bandwidth.

The audio output of this receiver can go directly to the line-level input of a tape recorder or audio amplifier. It works well with the RADIO SHACK mini amp which has 5000 ohms input impedance, Radio Shack cat no. 277-1008C, but any battery-powered audio amplifier will work for whistler reception.

Designed with a minimum number of parts for simplicity, and direct input coupling for maximum gain. This receiver can even receive direct current (DC) across the input.

Do not leave out any parts, proper DC bias is applied through this combination of parts.

This circuit is designed to work with STORMWISE antennas of 20 KHz or lower having a prefix of "C" or "AF" in the part number. Example C10T-1K-2K-BC or AF10T-0.5K-1.5K-BC.

The Stormwise antenna works to convert the radio wave's magnetic field into an electrical radio wave voltage that is a perfect match for this type of high-impedance receiver.

Power this JFET receiver with a 9-volt battery. Power your recording equipment with battery or use a microphone - speaker to isolate outdoor receiver to indoor powered equipment.

  • Antenna is one of our VLF or ULF antennas with "C" or "AF" prefix in part number.
  • Q1 is an MPF-102 N-channel field effect transistor.
  • R1 is a 1 Meg-ohms resistor. Required for wide band operation, good sound.
  • R2 is a 10 K-ohms resistor. Required for operation. Input matching.
  • R3 is a 3.3 K-ohms resistor.
  • R4 is a 10 K-ohms resistor.
  • R5 is a 10 K-ohms resistor.
  • C1 is an 10 uF capacitor.
  • C2 is an 47 uF capacitor.
  • D1 is a 1N914 diode. Protects the JFET from static damage.
  • D2 is a 1N914 diode. Protects the JFET from static damage.
  • SW1 is a pushbutton ON-OFF switch of any kind.

    C1 controls the low frequency cut off of the receiver. Its like a tone control function. If too much low frequency comes in then change C1 to an 0.22 uF.

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

    How to build it: Print out the above circuit diagram. Scale it down on your printer or photoshop program so that it is large enough for the electronic parts to fit the dots. This size is @ 5.0 inches wide by @ 2.3 inches high. 112 dpi. Get some copper tacks from the hardware store. Get a small piece of wood. Cut out the paper circuit diagram printout and tack it to the wood, one tack going into each dot in the diagram. Place the parts on the tacks. Solder. Do not bend the JFET's leads too much. Place the JFET last after all the other parts to prevent static damage or heat damage. It is best to just let the JFET sit on top of the tacks and barely solder it to the top of the tacks. HAVE FUN!

    VLF and ULF signals penetrate walls of homes. You will find however that for very best performance and to get rid of the power line hum noise, you should operate the receiver at a good distance away from the power lines that run down your street. You will also find that there is (in most cases) one direction which the noise lower. Rotate and tilt the antenna until the lowest noise spot is found.

    Keep the wire leads short length between the receiver and the antenna, no more than 2 feet. Coaxial cable has about 20 pF capacitance per foot so this figure will add into the tuning capacitance value across the antenna, which may cut off the high frerquency range you may want to hear. To be safe, just keep the connecting wires to the antenna less than 1 foot long. A twisted pair of wires 1 foot long has less capacitance than a 1 foot coaxial cable.

    Some carbon-zinc 9-volt batteries create a random crackling sound in the receiver, (even without the antenna connected) by generating noise in the battery itself. Use a 1000 uF capacitor across the power terminals to eleminate any battery jitters that could occur.

    Use battery power only to prevent extra power line hum noise.

    This graph shows the approximate frequency response of this receiver based on frequency response of various C1 capacitor values from 0.1 uF to 1.0 uF. The starting cutoff point is at 750 ohms which is 4.4 times lower than the 3.3 K-ohms source resistor.

    The point on the graph above 750 Hz (the red line) is the filter cutoff region. The point below the red line (below 750 ohms) is the operating range response.

    C2 should always be equal or larger than C1 for the strongest output signal.

    A 1.0 uF capacitor for C1 is good down to @ 210 Hz.

    A 0.47 uF capacitor for C1 is good down to @ 460 Hz

    A 0.22 uF capacitor for C1 is good down to @ 990 Hz.

    A 0.1 uF capacitor for C1 is good down to @ 2100 Hz.

    Based on the numerical progression of the measurements in this graph the following can be roughly calculated:

    A 2.2 uF capacitor - good down to @ 99 Hz.

    A 10 uF capacitor - good down to @ 21 Hz.

    A 22 uF capacitor - good down to @ 9.9 Hz.

    A 100 uF capacitor - good down to @ 2.1 Hz.

    A 220 uF capacitor - good down to @ 0.99 Hz.

    A 1000 uF capacitor - good down to @ 0.21 Hz

    A 2200 uF capacitor - good down to @ 0.099 Hz.

    A 4700 uF capacitor - good down to @ 0.046 Hz


    TUNING A RANDOM LENGTH LOOP ANTENNA FOR VLF RECEPTION

    The Stormwise antenna works great by itself. It also allows tuning random wire loops to allow powerful reception of weak signals.

    The above diagram shows how to tune a random length loop antenna for listening for whistlers and other natural emissions, and will also work for tuning longwave. The portable antenna by itself works great, but if you want to go for the very weakest signals then you can use a larger loop antenna and couple it into your receiver like shown in the above diagram. Aim the loop and the portable antenna for lowest hum level. Connect a ground rod to the loop antenna to drain away static electricity.

    How it works: The radio waves have a magnetic field that makes a small current flow in the large loop antenna. The 20 windings around the STORMWISE antenna concentrate the magnetic field (produced by the radio signal current) into the STORMWISE antenna. The STORMWISE antenna transforms this magnetic field into a radio wave voltage across the tuning capacitor, and this goes into the pre-amplifier and finally into your receiver.


    Adding more gain to drive headphones

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

    Radio Shack stores have most of the parts. The circuit was designed to use a Stormwise portable antenna having very high output impedance: This is any of our antenna part numbers starting with "C" or "AF".

    fet preamp

    This shows how to add a second MPF-102 JFET transistor to the receiver to allow the unit to drive a standard earphone or headphones.

    Some parts values have been changed and noted below for this two transistor receiver.

  • Antenna is one of our VLF or ULF antennas with "C" or "AF" prefix in part number.
  • Q1 and Q2 are MPF-102 N-channel field effect transistors.
  • R1 is a 1 Meg-ohms resistor. Required for wide band operation, good sound.
  • R2 is a 10 K-ohms resistor. Required for operation. Input matching.
  • R3 is a 3.3 K-ohms resistor.
  • R4 is a 10 K-ohms resistor.
  • R5 is a 10 Meg-ohms resistor. (the value was changed for this project).
  • C1 is an 10 uF capacitor.
  • C2 is an 0.22 uF capacitor. (the value was changed for this project).
  • D1 is a 1N914 diode. Protects the JFET from static damage.
  • D2 is a 1N914 diode. Protects the JFET from static damage.
  • SW1 is a pushbutton ON-OFF switch of any kind.

    Added parts:

  • R6 is a 50 ohms resistor.
  • R7 is a 150 ohms resistor.
  • C3 is a 220 uF capacitor.
  • C4 is a 220 uF capacitor.
  • T1 is Radio Shack Audio Output Transformer 273-1380.

    T1: T1 has 5 wires. You will use 4 of them. 1 is the green wire. 2. is the blue wire. 3 is white wire. 4 is red wire.

    Battery drain is only about 5 milliamps when powered by a 9 volt battery.

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


    Adding more gain to drive a speaker

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

    Radio Shack stores have most of the parts. The circuit was designed to use a Stormwise portable antenna having very high output impedance: This is any of our antenna part numbers starting with "C" or "AF".

    fet preamp

    This shows how to add a third MPF-102 JFET transistor to the receiver to allow the unit to drive an 8-ohm loud speaker at medium volume. This receiver has very good sensitivity and nice volume.

    Connect the output directly to a large 8-ohm speaker (of at least 3 inches diameter, minimum), having a wide frequency range for best sound.

    The speaker should have a minimum frequency response of 300 Hz on the low end and up to 5 KHz for the high end. If you are only interested in Tweeks and Dawn Chorus which occurs below 2 KHz, a larger "mid range" speaker with a maximum response of 3 KHz will do nicely.

    This project should be built on a shielded copper-clad circuit board to prevent negative or positive feedback.

    Positive feedback is a squeeling or howling sound.

    Negative feedback is when some of the output leaks back into the input, and it 180 degrees out of phase with the original signal and actually cancels the effective sensitivity. Avoid this by shielding each complete amplifier stage from the others.

    Shield each transistor stage from the next stage. Keep the transformer and the speaker away from the antenna or away from the input lines.

    Negative feedback can be observed by a reduction in the sensitivity (especially of the higher fequency range) of the unit when built on a solderless breadboard, and the ground shield metal plate is un-hooked from the ground side. Receiver will work on a solderless breadboard but you must use the metal plate under the breadboard as a shield. It is however best to shield each individual amplifer stage to be sure.

    Some parts values have been changed or re-numbered from previous projects so this list is only applicable for the above diagram.

  • Antenna is one of our VLF or ULF antennas with "C" or "AF" prefix in part number.
  • Q1 and Q2 and Q3 are MPF-102 N-channel field effect transistors.
  • R1 is a 1 Meg-ohms resistor. Required for wide band operation, good sound.
  • R2 is a 10 K-ohms resistor. Required for operation. Input matching.
  • R3 is a 4.7 K-ohms resistor.
  • R4 is a 10 K-ohms resistor.
  • R5 is a 10 Meg-ohms resistor.
  • R6 is a 4.7 K-ohms resistor.
  • R7 is a 10 K-ohms resistor.
  • R8 is a 100 K-ohms resistor.
  • R9 is a 50 ohms resistor.
  • R10 is a 150 ohms resistor.
  • C1 is an 10 uF capacitor.
  • C2 is an 0.22 uF capacitor.
  • C3 is an 0.22 uF capacitor.
  • C4 is a 10 uF capacitor.
  • C5 is a 220 uF capacitor.
  • C6 is a 220 uF capacitor.
  • D1 is a 1N914 diode. Protects the JFET from static damage.
  • D2 is a 1N914 diode. Protects the JFET from static damage.
  • SW1 is a pushbutton ON-OFF switch of any kind.
  • T1 is Radio Shack Audio Output Transformer 273-1380.

    T1: T1 has 5 wires. You will use 4 of them. 1 is the green wire. 2. is the blue wire. 3 is white wire. 4 is red wire.

    Battery drain is only about 10 milliamps when powered by a 9 volt battery.

    You may want to connect the output of this receiver to your oscilloscope and then adjust the resistors for maximum volume output and minimum distortion. If R8 is changed to 10 meg-ohms for example, distortion will occur on strong signals. You don't want distortion! If you put a sine wave into the input you should get a sine wave out, showing purity of tone coming through the amplifier stages without distortion. The parts values shown were chosen for minimum audio distortion using standard values.

    Adjusting some parts values may seem to make the unit SOUND louder, but be careful since this added sound is actually unwanted audio distortion. You can see this undesired effect on an oscilloscope.

    There is no technical help with the projects. This circuit is shown as an educational example only. Copyright 2013
    All rights reserved