1. EXPLORING VLF and ELF FREQUENCIES
By John Bailey M0MTW

2. EXPLORING VLF and ELF FREQUENCIES
1.What frequencies
VLF (Very Low Frequencies)
2.What can be heard?.
3. Professional VLF Radio Stations
4.Local Interference
5.Strange behaviour of radio at VLF
6.The receivers and Antennas
7.Analysing the signals – software
ELF (Extra Low Frequencies) – as with VLF
8.Next Projects
9.Online sources

3. The frequencies BAND Frequency ELF – Extremely Low Frequency 0.1 – 3Hz
SLF – Super Low Frequency
3 – 30Hz
ULF – Ultra Low Frequency
30 – 300Hz
VLF – Very Low Frequency
300 – 3kHz
 LF – Low Frequency
 3kHz – 30kHz
 MF – Medium Frequency
 30kHz – 300kHz

4. 300Hz to 3KHz (Commonly given as 300Hz to 30KHz)
Starting with VLF
300Hz to 3KHz (Commonly given as 300Hz to 30KHz)

5. VLF theory
As VLF wavelengths are very long they can diffract around large obstacles.
They can propagate as ground waves around the curvature of the Earth.
The Ionoshpere ‘D’ layer at 60kM reflects the VLF wave between this and Earth ground a duct a few VLF wavelenths high is formed.
The duct acts a waveguide waves following a zigzag path around the world.
VLF waves have very low attenuation 2-3dB per 1000kM.
Attenuation is low because VLF waves are reflected at such a low level unlike shortwave signals being reflected at higher levels and more affected by ionisation.
Propagation distances of 5000 to 20000kM can be achieved and are more stable than higher frequencies.
On the down side VLF signals are subject to more atmospheric noise.

6. Natural VLF radio signals
Static discharges – lightning
“spherics” atmospherics radiated by lightening.
Tweeks – sounds like twittering and is a deformation of the static propagating.
Insects – produced by current flowing between clouds and ground – frequency can vary with time.
Whistlers - reducing infrequency over periods from half to several seconds. Several types of whistler can be identified.
Auroral chorus – can sound like musical whistles, varying in both tone and frequency.
Flying Saucers – connected to aurora phenomenon.

7. Solar Flares Solar flares can be detected at VLF frequencies.
This is often achieved by continuously monitoring signal levels of military transmissions.
A Solar Flare is caused by the sudden collapse of the very highly strained magneticfield in the region of a Sun-spot.

8. Solar wind
The solar wind and cosmic rays can be monitored by VLF equipment.
Measurements taken by various space probes.
The solar wind deforms the earth’s magnetosphere.

9. Man made VLF signals
Submarines
Radio Navigation
Time Radio Stations

10. The varberg radio stati0n
The Varberg Radio Station at Grimeton is a VLF transmission facility at Grimeton near to Varberg, in Halland, Sweden.
It has the only working Alexanderson alternator rotating armature radio transmitter in the world.
200kW Output

11. The varberg radio stati0n
The transmitter was built in 1922 to 1924 to operate at 17.2 kHz.
The antenna is a 1.9 km (1.2 mile) flattop wire aerial consisting of eight horizontal wires suspended on six 127-metre high freestanding steel pylons in a line.
The Grimeton VLF transmitter location is also used for shortwave transmissions, FM and TV broadcasting.
Upto the 1950s, the Grimeton VLF transmitter was used for transatlantic radio telegraphy to Radio Central in Long Island, New York, USA. From the 1960s until 1996 it transmitted orders to submarines in the Swedish Navy.

12. Grimeton Reception reports
Grimeton transmits twice a year on 17.2kHz CW, at the end June / beg. July (Anderson Day)and Christmas Eve (extra transmission 16th August 2016)
Above is the reception report from 3rd July 2016

13. SAQrx software SAQrx is a soundcard based receiver covering 0-22kHz.
Was written to allow listening to the Grimeton transmissions.
Is available to download free from SM6LMK

14. MILITARY STATIONS
VLF Transmitter - Yosami , Japan -In April 1929, the Yosami Station established the first wireless communications between Japan and Europe with a long wave operating at kHz. An inductor-type high-frequency alternator provided output power at 500 kW.
The antenna system used eight towers, each 250m high. The facilities were used for communicating with submarines by the Imperial Japanese Navy from 1941 to 1945 and by the United States Navy from 1950 to 1993.

15. Strange behaviours of radio waves at VLF frequencies.
Penetrate water ~ 40meters in saltwater. Very large wavelengths mean signals are not blocked by mountain ranges. Suffer little of fading experienced at other frequencies. Subject to high atmospheric noise (sferics) like whistlers caused by lightening.

16. Difference between electric and magnetic field
To listen to VLF signals you need to choose between electric field and magnetic field receivers.
The differences are small as both carry the same information.
Example a VHF FM signal received with a whip aerial receives the electrical component whilst long waves received using a ferrite rod aerial receive the magnetic component.
Generally the antenna to receive the electrical component is most often used as its easier to construct.

17. Interference & noise. Mains Hum – harmonics extend to over 10KHz
Signals from high voltage power lines.
Electric motors
TV-Line timebase.
Radio navigation
Military RTTY

18. 50Hz mains harmonics
A problem at lower VLF frequencies.

19. Other disturbances Local obstructions Trees shielding signal.
Insects – weak electrostatic field variations – sensitive electric field receivers with whip antennas.
Static discharges from clothes
Wristwatches - when using a magnetic field receiver the weak VLF magnetic fields of wristwatches are detectable.
Cars –Ignition noise is detectable from 200meters distance.

20. OPERATING LOCATIONS Remote
Away from sources of interference – mains hum – power lines
No obstructions
Away from industrial areas

21. ANTENNAS
Trideco" antenna tower array at the US Navy's Radio Station in Cutler, Maine, USA.
The central mast is the radiating element, with a star-shaped horizontal wire array.
About 1.2 miles in diameter, it communicates to submerged submarines on 24 kHz at a power of 1.8 megawatts, the most powerful radio station in the world

22. ANTENNAS US Navy Communications Station , Panama.
Established in 1908 in use upto 1960s?
A cryptographic centre and a fleet broadcast centre

23. Audio Clips What do they sound like : Whistler Dawn Chorus
Pure whistler
2 hop whistler

24. Audio Clips 2 Auroral chorus Periodic emissions Magnetic Storms
Flying Saucers
Distant thunderstorms

25. NASA INSPIRE VLF-3 Receiver
WR-3 ELF/VLF Receiver
Commercially available equipment
NASA INSPIRE VLF-3 Receiver

26. Homebrew equipment
Lots of handheld equipment because its portable and can be operated in quieter more remote locations.

27. VLF BBB4 electric Field Receiver (steve McGreeevy)
MY EQUIPMENT
VLF BBB4 electric Field Receiver (steve McGreeevy)
High impedance input.
Short whip antenna
Portable
Simple circuit with good performance.

28. I added a 50Hz Filter to reduce mains hum
BBB4 Circuit
I added a 50Hz Filter to reduce mains hum

29. The floating receiver

30. The floating receiver How it works
The floating receiver is a variant to the electric field receiver.
Instead of taking the signal between the antenna connection and ground it’s taken between two symmetrical antenna terminals.
By avoiding the ground connection the receiver has two advantages :-
- Illininates noise from the ground connection, collects signal present in the air only.
- Avoids noises from the PC through connecting cables.

31. THE FLOATING RECEIVER Constructed on veroboard.
Resistive bridge 2x 100M resistors using 10x 10M resistors in series.

32. Antenna is not resonant and can be small.
MY EQUIPMENT
*Antenna 5” drain pipe *2 sheets heavy duty aluminium *Each sheet separated by 100mm *Receiver located inside drain pipe to weather proof. *Connected by 10metres of screened cable to pc.
Antenna is not resonant and can be small.

33. * Spectran – I2PHD / IK2CZL * Spectrogram – Richard Horne * SDR#
Analysing the signals – software
FFT (fast Fourier transform software)analysis of the received signals.
* Spectran – I2PHD / IK2CZL * Spectrogram – Richard Horne * SDR#

34. Has an effective mains hum filter included.
Spectran
Has an effective mains hum filter included.

35. Graphical representation of signals
WHISTLER

36. Spectum Lab
TWEEKS

37. ELF frequencies (the sub-audio band)
Extremely low frequency (ELF) is the ITU designation for electromagnetic radiation (radio waves) with frequencies from 3 to 30 Hz, and corresponding wavelengths from 10,000 to 100,000 kilometers.
In atmospheric science, an alternative definition is usually given, from 3 Hz to 3 kHz.

38. Difficulties of ELF communication
About ELF frequencies
Difficulties of ELF communication
ELF waves propagate slightly slower than the speed of light in a vacuum.
Wavelengths are extremely long comparable to the earths diameter.
Two US maintained sites, one in Chequamegon-Nicolet National Forest, Wisconsin and another in the Escanaba River State Forest, Michigan
-these use long ground dipoles with multiple strands ranging from 22.5 to 45 Kilometers.

39. ELF effects on human nervous system
ELF Frequencies
ELF effects on human nervous system
A study in 1999 showed that the threshold for direct perception of exposure to ELF RF by human volunteer subjects started at around 2 to 5 kV/m at 60 Hz, with 10% of volunteers detecting the ELF exposure at this level.
ELF at human perceivable kV/m levels was said to create an annoying tingling sensation in the areas of the body in contact with clothing, particularly the arms, due to the induction of a surface charge by the ELF.

40. ELF Antenna A half wave dipole for 80Hz would measure 1162miles.
Elf transmissions through the earth need very high transmitted power in the mega watt range.

41. Uses of the ELF Band Submarine communications.
Railways – Norwegian rail system supplies 16kV AC at 16.66Hz to its engines.
HAARP – Auroral Research based in Alaska.
Mains networks.

42. ELF Frequencies

43. Natural Signals in the ELF band
Schumann resonances discovered in 1952 by W O Schumann. Formed by excited statics within the cavity between the earth and the ionosphere.
Long distance sferics.
Whistlers and Hiss – 200Hz down to 20Hz taking upto a minute to pass.
Magnetic Pulsations – formed in the magnetosphere.

44. Graphical display
Shumann Resonances

45. Simple ELF Receiver

46. ELF Antennas

47. Research groups
Stanford VLF Group - The Stanford ELF/VLF group is exploring an alternative method of ELF/VLF wave generation, which utilizes the same currents that make the northern lights, to turn the upper atmosphere into a big radiating antenna.
The VLF ELF Radio Research Institute - it carries out research into VLF and ELF radio waves, particularly naturally generated waves in the Earth's atmosphere, magnetosphere and ionosphere, such as whistlers and chorus.
NASA – solar storms and space weather reports.
The High Frequency Active Auroral Research Program (HAARP)

48. Using a PC soundcard
Basic principle The pc soundcard is used to convert the vlf signal into an audible signal. frequency is converted down to an audio frequency of 650hz. Just connect some meters of wire as an antenna to the mic input of the soundcard and try to listen to a local signal source. Add a simple lc network parallel to the input as vlf preselector this will protect your soundcard if you connect a longer piece of wire An active antenna can also be used.

49. Online VLF receivers https://www.ab9il.net/vlf/vlf1.html LOCATION
STREAM TYPE
DELFT, NETHERLANDS **Software Defined Radio**
Tuneable SDR
CAPE CORAL, FL, USA
MONO
SEBRING, FL, USA
MARLTON, NJ, USA
HAWLEY, TX, USA
BIELEFELD, GERMANY
CUMIANA, ITALY
SHEFFIELD, UK
TODMORDEN, UK
BIELEFIELD + CUMIANA
STEREO
MARLTON + SEBRING
TODMORDEN + BIELEFIELD
TODMORDEN + MARLTON

50. NASA Online VLF receiver

51. Next project RCM2 Easy Loop Antenna IK1QFK
Uses single Op amp amplifier
75cm 40 turn Loop Antenna

52. NEXT PROJECT/s ELF Receiver
SID Receiver -Sudden Ionospheric Disturbance Receiver – detects solar flares and gamma ray bursts.
Fluxgate Magnetometer – measures the intensity and orientation of magnetic lines of flux.
WSPR 137.5KHz 2200M Beacon transmitter.

53. Further reading/sources
Books:
RSGB – RADIO NATURE –
By Renat0 Romero, IK1QFK
ISBN:

54. Thankyou for listening
THE END
Thankyou for listening