Solar X-rays:

Geomagnetic Field:

ELF is from 3 HZ to 30 Hz.

VLF is from 3 Khz to 30 Khz

ULF is from 300 Hz to 3 Khz

ULF and VLF are most often picked up by the same receiving equipment. ELF requires special circuitry and is not often found in the frequency range of receivers that emphasize a range that starts at 300 Hz or higher. On this site, VLF and ELF are separate bands requiring different circuitry, and ULF is not specifically mentioned.

The Ionosphere acts as a waveguide for electrical and magnetic waves caused by lightning, solar activity, and other atmospheric phenomena. When there is a lightning strike somewhere in the world, waves are generated. These waves are not sound (acoustic) waves. They can only be “heard” by special receivers.

It can be confusing as you read material on various web sites on the subject of VLF and ELF. But all the material can be divided into 3 categories:

1. Solar activity can be monitored indirectly by measuring the signal strength of VLF transmitters. For example, there is a 2 megawatt VLF transmitter in Maine, USA, which transmits information to submarines underneath the ocean. When solar activity occurs, or when dawn or dusk occurs, the strength of this type of transmitter is affected. A VLF receiver & recorder can pick up these transmissions and record the amplitude (signal strength). The resulting charts can be compared to solar activity readings from NASA and other sources to see if they correspond to each other.

2. ELF receivers are designed to monitor natural events, such as earthquakes, tremors, or other phenomena in the Earth or atmosphere that create extremely low frequencey waves.

3. The third category is a receiver that will pick up Whistlers, Sferics, and tweeks. These waves are caused by lightning. Lightning can strike clear around the Earth, and electric and magnetic waves are generated. The waves are picked up by receivers which convert the waves into sound.


There are 3 subjects that VLF / ELF web sites and books usually deal with. These subjects  can become confusing, since many of the web sites describe electronic circuits and other information without explaining their context. On this web site, my goal is to explain the context first, and then specific information about each subject.

1 - ELF monitoring of magnetic and electrical waves & natural phenomenon such as earthquakes and tremors.

2 - Whistlers, Tweeks, & Sferics, direct monitoring via VLF receivers.

3 - SIDs (Monitoring indirectly by measuring the signal strength or amplitude of waves coming from transmitter stations). SIDs are “Sudden Ionospheric Disturbances.”


There are 2 types of receivers, magnetic and electrical wave receivers. Electrical wave receivers generally use vertical  antennas, and magnetic receivers generally use magnetic coils of various sizes and shapes.



A YouTube video - listening to Sferics & Tweeks using spectrum analysis software...  Uploaded on Jul 18, 2011 Almost everything in one recording  made on the 17th July 2011. This short track has Sferics,Tweeks,  Whistlers, Local Lightning, Rain Noise, ................. Dawn Chorus?  No its Boyzone. Recent weather conditions have brought low cloud from  the East and rain, still open for more investigation I believe the cloud and falling rain forms a duct between my antenna and the local MWave AM Pop Station 1.5km away. The protection diodes in the front end provide  some non linearity for detection. The music and vocals can be seen at  the bottom of the spectrum.