Amateur Radio Communications Below 9kHz


See https://sites.google.com/site/sub9khz/ for up-to-date information on all aspects of sub-9kHz amateur radio.


Maintained until sub-9kHz website created earlier this year. See above site for most recent information.


A very busy 8-9kHz amateur band in March 2011. This screen shot from DK7FC's grabber shows just how busy this band is now becoming and how much progress has been made in the last 12 months. Visible in the grab are DJ8WX, OE3GHB, DK7FC (local testing) and DF6NM.

Click on the image to see all the traces more clearly.

Latest News




  • OK2BVG copied in Todmorden UK at a distance of 1423km last week using just 25W RF!
  • DJ8WX has been on 8.970022kHz again 13.3.11 but only weakly copied by G3ZJO and G3XBM in the UK.

  • Video of my VLF receiving system now available (see right). This has now received 3 different stations (G3XIZ, DJ8WX and DK7FC/P)
  • DJ8WX copied by G3XBM (645km) with SL in 423uHz bandwidth on 8.970022kHz overnight and all day today 4.3.11. Also copied by others (G3ZJO and Paul Nicholson).

  • DJ8WX copied by DK7FC and OE3GHB on 8.970.022kHz 3.3.11
  • G3XIZ copied here (by G3XBM) at a distance of around 45km using Spectrum Lab with 423uHz bandwidth. He was also seen by Paul Nicholson in Todmorden Yorkshire at 218km - a new record for a UK VLF amateur.

  • OE5ODL copied in Israel on Feb 17th on 8.97kHz. DX is 2478km.He has also been copied in Iceland on TF3HZ's (OM Halldor) excellent Icelandic VLF grabber at a distance of 2763km.
  • PA3CPM received by PA3FNY on 8.920 kHz. DX was 3km. Not sure what TX, antenna or RX used yet. I believe this is the first Dreamer's Band activity in The Netherlands.
  • DK7FC/P copied well on 8.97kHz Feb 6th in Iceland (2404km) during his 10th VLF test. Later in the day, when I'd fixed a
    fault, I managed to copy Stefan at up to 10dB S/N in a 4.52mHz bandwidth using the small preamp shown below.The screen shot shows how strong he was using this simple receiving set-up. Anyone can copy him! Stefan's report on the test may be found at http://dl.dropbox.com/u/15047843/dk7fc_10th_report.rtf .


  • OE5ODL and OE3GHB were active Jan 22/23rd and widely copied from their home QTHs. OE5ODL copied by Paul Nicholson at 1252km in Todmorden Yorks UK.
  • DL3NDR and Walter DJ2LF have worldwide first character-based VLF-QSO over 4km on Jan 23rd 2011.
  • G3XIZ copied by M0BMU on 8.97kHz at 37km - a new UK record.
  • New VLF grabber operational in Iceland. See http://simnet.is/halldorgudmunds/
  • DK7FC copied in Israel on 8.97kHz at 2873km!!! Also copied at G3XBM's QTH (weakly) with earth electrode antenna on RX. Read Stefan's report on his 9th experiment.
  • 4X1RF has installed a VLF grabber in Israel
  • G3XIZ carried out an unsuccessful test with 20W to a Marconi antenna on 22.11.10
  • G3XBM has installed a VLF grabber in JO02dg active during tests
  • LA3EQ has done a first VLF WSPR tests on 8.76kHz over short distances
  • DF6NM made a successful 6.47 and 8.97kHz kite transmission 13.11.10 with positive reception in Todmorden UK by Paul Nicolson.
  • OE5ODL manages to get 10km on 8.970kHz using a Marconi vertical, top loaded, with 250W out (reported 6.11.10). This is the first Austrian VLF activity.
  • G3XBM started VLF tests on 8.760kHz 3.11.10 using 4W to grounded electrode antenna. Best DX 5.1km using utilities assisted earth mode.
  • DK7FC kite tests on VLF on 23.10.2010 were a GREAT success with signals being received across W.Europe as far as Eire, a new DX record of 1310km. Transmissions took place on 8.97KHz, 6.47kHz and 5.17kHz. Congratulations to Stefan and all stations who managed to receive him. Some reports were so good that QRSS60 would have been copyable.
  • DK7FC is planning a further radiated DX test on 8.97kHz and 6.47kHz on Oct 2nd using his kite supported antenna. UPDATE: good reception in Poland (902km), in Germany, Holland and the UK. A successful test so far. Stations in N.America also looking for the signals.
  • New Yahoo group formed called Sub-9kHz Amateur Radio open to anyone interested in communicating or beaconing in this part of the spectrum
  • On Sept 25th DK7FC managed to send a message "CU" to Michael Oexner using the earth electrode antenna (see picture on right)
  • On Aug 29th DF6NM became the second station to exceed 100km on VLF when his signal was copied 180km away. Also this weekend DK7FC's 250w transmission into 600m spaced earth electrodes was copied 49.6km away.
  • On Aug 1st 2010 Stefan DK7FC conducts tests on 6.47kHz with 11mW ERP using a 200m kite antenna and is received across Germany and in France (by F5WK at 460km) and in the UK by Paul Nicolson at 859km.
  • On June 4th DJ2LF and DF6NM held what was probably the first two-way contact QSO on 8.97 kHz. The distance between them was 20.2 km, well outside the reactive near field zone (lamda / 2pi = 5.3 km). In each case the radiated power was about 5uW. They used a special QSO procedure using dual frequencies. Congratulations to both stations.



INTRODUCTION

One of my interests is ELF/VLF with my final year university thesis (now nearly 40 years ago!) being on whistlers and related atmospheric phenomena below 9kHz. This interest started in the mid 1960s when experimenting with communications through the ground using frequencies below 9kHz (see my article in RadCom April 1975). This form of communications is sometimes known as Earth Mode or Earth Current. Currents are injected into the earth or rock via 2 electrodes and detected some distance away as a potential difference between 2 further electrodes driven into the earth or rock. Filters are usually needed to reject mains hum as this can be the limiting range factor in urban areas. In open areas well away from cables and pipes, signals attenuate very rapidly with distance (-18dB every time distance is doubled) so most people are unable to cover more than 0.5-1km with low power amplifiers and electrode spacings of 10-20m. With 500W - 1kW audio amplifiers ranges up to 10km have been achieved at around 6-9kHz. Greater earth mode DX is possible using modern weak signal techniques. Articles on this form of communications have appeared in radio magazines many times over the years. My own interest was first awakened by a couple in Practical Wireless in 1964 and 1965. In recent years earth current or earth mode communications has proved effective for cave communications and rescue work with depths of some 800m being covered into cave systems. Earth mode was popular in the USA during WW2 (see QSTs from 1942) when conventional ham radio was not allowed.

My own best DX with VLF earth mode using 4W QRSS3 at 838Hz and using a 20m earth electrode TX "loop in the ground" is currently 5.6km receiving the signal on an 80cm loop, preamp and PC running Spectran. See Earth Mode and Induction at VLF for regular updates.

With modern detection techniques, amateurs can radiate and detect signals over a reasonable distance in the 8-9kHz band. Some have speculated that ranges up to a few hundred kilometres might be possible, something considered impossible even very recently, and recent tests have confirmed remarkable distances are indeed possible, but clearly producing any serious amount of radiated power requires a well engineered transmitter and antenna system.


VLF WORK IN GERMANY

Several amateurs are now getting seriously interested in operating below 9kHz to see just how far an amateur signal can be detected. The DX record was held by DF6NM for reception of his 35W signal at a distance of 12.1kms using very narrow band signal detection techniques (see chart lower down the page). His  antenna is quite small (9m effective height at 137kHz) and his loading coil big (1.4 Henries). For receive Marcus was using a 6m long wire antenna.

DK7FC did further tests on 8.97kHz on 15.3.10 using a 100m long kite mounted vertical Marconi antenna with a huge loading coil and 250W RF input (ERP 1.7mW). He was received in Germany (180kms) and in the north of the UK (857kms) although no identifiable callsign was received in the first test. A week later his next test transmission was copied by several stations across western Europe with the best DX reception being from 902kms away.  Reception was only possible with very narrowband software based filtering using very slow QRSS but at least we now know that amateur signals on the 8.97kHz (33kms!) "Dreamers Band" can travel a very long way indeed. For more details of Stefan's equipment see http://www.qrz.com/db/DK7FC. For some plots of signals received in various DX locations see http://abelian.org/vlf/ss100321/ .



This is a screenshot of DK7FC's signal as seen at DF8ZR/Bernd's QTH in QRSS30 mode (16kms) during the first test on March 15th.

On the right shows Stefan's enormous base loading coil and the picture below the kite used to keep the vertical wire aloft.















UPDATE:  On Aug 1st 2010 DK7FC experimented with a 200m kite antenna on 6.47kHz. Although QRN was high, several stations managed to copy his signals:

DF8ZR (QRSS-60 mode, 16km)
DK7FC (grabber in DFCW-240 mode, 40km)
DD7PC (congrats, first time! 53km)
DF6NM (insecure, fragments, 180km)
DL4YHF(impressive S/N!, 264km)
F5WK (460km)
Paul Nicolson (859km) Best DX reception of the lowest signal, transmitted by an amateur so far (far field) - see image below and more details at http://abelian.org/vlf/ss100801/ and http://abelian.org/vlf/ss100801/todmorden4.png





SPECIAL RESEARCH PERMITS (NoVs) in the UK?

In the UK, OFCOM has stated it will seriously consider the issuing of Notices of Variation (NoV) for operation below 9kHz on a case-by-case basis and applications are being made by some UK amateurs. With this latest news of radiated emissions success these can't come soon enough. The latest update on my own NoV application is that OFCOM is awaiting a response from the Met Office who have an interest in sferic detection below 9kHz. Hopefully this will not take too much longer.

HISTORY AND MILITARY USE



First use of Earth Mode goes back to WW1. This interesting piece was found at the IEEE site

    Ferrié, Gustave-Auguste
    (19 Nov. 1868 - 16 Feb. 1932)

    Engineers had long known that telegraph signals could travel a few hundred yards through the ground, but little use had been made of this form of wireless communication. In 1914 the enterprising engineer Gustave-Auguste Ferrié, who headed the French Radiotélégraphie Militaire before and during World War I, recognized two things: the newly available electron tube could significantly extend the range of this technique; and it might then be of enormous value in the fighting on the Western Front. Thus was born ground telegraphy or Earth-currents signaling.

    Ferrié made improvements in the signal generator and in the receiver -- notably by the use of a triode amplifier -- and achieved a usual range of several kilometers. The transmitter was essentially a buzzer (an electromechanical device that interrupts the circuit at a very high rate) powered by a battery. The receiver was an amplifier, employing a triode electron tube. Earth connections were usually made by driving steel pins into the ground; often a short length of insulated wire was laid along the ground and anchored at each end by a spike.

    These devices began to be used in large numbers in 1916, and by the end of the war the French had produced almost 10,000 of them for use by the Allies. The Germans also deployed a system of ground telegraphy; it was mainly the work of a young mathematician, Richard Courant, who became famous after the war for his work on quantum mechanics. The famous physicist Arnold Sommerfeld also contributed to the German development of ground telegraphy. In the United States, Lee de Forest patented a system of signaling by Earth currents.

    Users of ground telegraphy discovered that their receivers frequently could pick up telegraph and telephone signals from lines buried nearby. They were thus used to tap enemy lines and also to receive one's own telegraph or telephone signals when a line had been severed. These receivers came to play a large role in eavesdropping. Its portability and its freedom from electrical lines made ground telegraphy an important means of communication during the Great War. It was a technique, however, that scarcely outlived the war. Even before war's end it began to be displaced by another wireless communication technique. This, of course, was radio, the technology to which Ferrié devoted most of his efforts.

The military used "earth mode" in the 1960s for secure communications between buried nuclear installations. More recently they have used extensive ELF arrays to communicate with submarines but this is actually using radiated signals rather than conduction currents.

Radio amateurs have tried "earth mode" at 73 and 136kHz with some success, as have cavers. With modern weak signal detection methods, e.g. waterfall displays on PCs, signals far too weak to hear can be "seen" as traces on the screen.

Another mode useful for Earth Mode is PSK31 which is a very narrow band data mode. Most PSK31 stations use PC sound cards to do the digital signal processing making this one of the easiest digital modes to use. The data rate allows up to 50wpm in bandwidths of about 31Hz (hence the name).

Foremost in sub-9kHz through the ground communications was John, G0AKN, who sadly is a silent key. A paper on his work is available as an attachment on this page (see bottom of page).


9kHz RECEIVING EQUIPMENT

Jim M0BMU has produced a neat loop/preamp design suitable for listening on the 9kHz band. His design has sufficiently low noise to provide a state-of-the-art receiver for this band when used with the many excellent software based VLF receivers such as Spectran and Spectrum Lab. This (rev B) circuit was posted on the LF Reflector on March 23rd 2010. 
Jim recently posted some design notes on the VLF loop and preamplifier:


There are basically 3 frequency response determining elements in the design. The first is the loop inductance, the shunt input capacitance C8, and the input resistance of the preamp (about 300R, determined mostly by resistors R1, R2 and R4, which also set the gain of the input stage). These together form a singly-terminated, second-order low pass filter with a roughly Butterworth response and cut-off frequency something over 20kHz. The preamp stage gives about 30dB gain, and a reasonably low noise level - evidently below the external band noise. This was arrived at after some back-of-envelope calculations and tests of likely noise levels, induced EMF in the loop, and so on.

The second element is the op-amp gain stage IC1A. This is configured as a "lossy integrator", with a gain that rolls off at 20dB/decade in the operating frequency range. This compensates for the loop output, which rises at 20dB/decade below its cut off frequency, due to the loop EMF being proportional to d(phi)/dt. It isn't essential to do this, but I felt this would be useful in comparing noise levels, etc., and reduce the likelihood of overloading by VLF utilities. At 9kHz, the gain of this stage is about 30dB also; the overall 60dB gain gave a good signal level for the audio line input socket on my lap-top, determined by trial and error.

The final element is the bandpass filter. This was a straightforward ladder filter designed with a n=3 Butterworth response, with the component values fiddled a bit to suit off-the-shelf inductors. I aimed for an impedance level that could easily be driven by normal op-amps. The filter is terminated by 1200ohm resistors R10, R11, which are necessary to give the correct response (actually, the initial design values were about 900ohm or something, but I increased the value to "absorb" the loss resistance of the rather low-Q 4.7mH inductors). The IC1A stage has a high input impedance that does not load the filter significantly, but the input preamp stage has a fairly high output impedance, and its gain would also be affected by connecting the filter as a load. So the IC1B buffer stage was included, which also provides 9dB gain to make up for the 6dB loss between the terminations, plus approximately 3dB insertion loss of the filter.

So all the parts of this circuit were designed to work together - if you wish to build a circuit with a different antenna, or use the filter in a different system, you need to take similar considerations into account - there are a near-infinite number of feasible solutions that will perform as well or better, but all will have differences.

Cheers, Jim Moritz
73 de M0BMU

Jim M0BMU has since modified his circuit so it functions as a complete 8.97kHz direct conversion receiver. He posted a description and a schematic on the LF-reflector (see below).

Regarding portable receivers for 9kHz, I have now added a BFO/product detector/AF output to my 9kHz loop/preamp/filter circuit. This effectively converts it into a small, self-contained fixed-tuned upper sideband receiver for headphone aural reception around 9kHz. The sound card preamp function is still available of course. The main idea of this was to have a portable receiving system for investigating noise sources at 9kHz, but it would also work well for near-field transmission experiments that people are trying. I also have an up-converter which can be used in conjunction with an FT817 as a portable 9kHz RX, but the dedicated circuit is much smaller and simpler, and more convenient. It only consumes about 20mA or so from the 12V supply, so only a small battery is needed.

The attachment shows the complete circuit - The 7.5kHz BFO and product detector uses a 4053 CMOS analogue switch IC as a combined mixer and RC-tuned oscillator. There is a bit of an explanatory diagram at the bottom of the schematic as to how this works... The BFO frequency stays within about 100Hz, which is fine for aural reception - for narrow band modes needing higher stability, down conversion can instead be performed by a PC and sound card of course.

The overall audio gain between loop antenna input and headphone output is very high, and when the "wide band" 3 - 22kHz bandwidth is selected, oscillation can occur due to internal ground loops, or external coupling between loop antenna and headphones. But for listening purposes, the wide band setting is not very useful anyway, and feedback is not a problem when the bandpass filter is selected since then input and output are in different frequency ranges. The complete circuit is contained in a small diecast box - however, I found this is not very effective as a shield against magnetic fields at 9kHz - best to keep it some distance from any lap-top or PC which it is connected to.

It is quite interesting to walk around with loop and RX listening to the wierd buzzing and whirring man-made noises and mains hum that is superimposed on the background QRN around 9kHz, and a good way of checking the suitability of a receiving location for future 9kHz tests. I have found that if you stand near overhead power lines, the noise present sounds quite different depending on the orientation of the loop with respect to the overhead wires. I guess this is due to different levels of 50Hz harmonics being present in the differential-mode and common-mode currents flowing in the lines. If you try this, you can expect very strange looks from passers by ;-)


M0BMU's Portable VLF Receiver Schematic


Other possible receiver front ends and antennas include variations of the voltage probe antennas using high impedance input stages and short whip antennas. Examples include the BBB-4 from S.McGreevy, possibly with some changes to increase the response around 9kHz. See http://www.auroralchorus.com/bbb4rx3.htm


MODERN DX RECORDS

The table below gives a summary, as best I know them, of the distances amateurs have so far covered below 9kHz. If you have more data, please let me have this so I can update the chart. In the coming months with several German and UK stations experimenting, the DX record is likely to be smashed. It is doing the impossible that has always driven radio amateurs. At VLF everything is "up for grabs" as far as records go.

 Callsign Freq (kHz)
 TX Power (W)
 Antenna DX
(kms)
 NotesRX bandwidth
 DK7FC/P 8.97550 (58mW ERP)
300m vertical
2873
Best radiated DX recorded so far by 4X1RF
4.5 or 3.8 mHz
 DK7FC/P 6.47
550 (11mW ERP)
200m vertical
904By SQ5BPF      
 DK7FC 5.17
150300m vertical904By SQ5BPF
 
 DK7FC/P 8.97250600m earth electrode
49.6Received by Michael Oexner (JN49BF). Full message "CU" received in DFCW some weeks later.
 
 SP2KDS 9.6600E-field long wire 30m high and 110m long290RX station was SQ5BPF 
 DJ8WX 8.97750
Marconi top loaded vertical
779Copied by DK7FC, OE3GHB, G3ZJO and G3XBM 
 
 DF6NM 8.97
35
0.2 mW EMRP
Vertical180
Using DFCW-600 and DFCW-6000.
[Also 2-way QSO with DL2LF at 21km]
 
 OE5ODL 8.97
350?90m balloon supported vertical?
2763
Received by in Israel on Chris' grabber (2478km) and  in Iceland on Halldor's excellent grabber at a distance of 2763km424 uHz and 100uHz
 OE3GHB 8.97220 (Alpine 3541 Audio-PA)16m high Marconi with about 100m of horizontal topload (~600pf)590Copied in Germany and now Poland by SQ5BPF  
 G3XIZ 9.0909
150
Inverted-L45
218
Received by G3XBM 3.3.11
Received by Paul Nicholson (Yorkshire)
423uHz
40uHz
 G0AKN 6.01000Grounded electrodes
10Best DX with earth-mode (conduction)
 
 OK2BVG 8.9725 (300mA ant current)
 24m vertical with 220m top
1423
Received by OE3GHB March 5th 2011
and by Paul Nicholson Todmorden UK at 14dB over noise in 80uHz BW
80uHz
 W1VLF 8.954Vertical5  
 PA3CPM8.92
 2510m sloper
3Copied by PA3FNY
 
 K6VLF 1.8100B-field3.3Identical antennas at TX and RX sites. 300ft long-wire in closed single turn loop. Non-grounded system.
 
 DL5KZ 104Grounded electrodes
3  
 DJ2LF 8.9714E-field20.52-way QSO with DF6NM
 
 VK2ZTO 8.98380Grounded electrodes1.6  
 DK8KW 8.9310E-field1  
 G3XBM 8.7604
20m spaced earth electrodes
5.1Received using 80cm loop/preamp (earth mode conduction)
QRSS3
 G3XBM 0.8384Grounded electrodes TX, 80cm loop RX
5.6 
20m TX electrode spacing, 80cm RX loop. DX aided by "utility coupling" to underground pipes (Earth mode conduction)
QRSS3
 G6ALB 8.7640 Grounded electrodes TX, EFP at RX end
3Utilities assisted earth mode
QRSS3
 IW3SGT 8.98 0.1  
 DO1KHS 8.7940Vertical0.1  

19th century DX
William Preece spanned 5kms in 1892 with induction communications across the Bristol Channel (see J.J.Fahie's book below) albeit with huge induction coils at each end. This pre-dates Marconi's true radio tests by several years.


VLF TRANSMITTING EXPERIMENTS IN THE USA

Paul W1VLF is getting operational on the 33kms band (8.97kHz) and has already been received 5kms away running 50W into a base loaded vertical. He has created a website to detail the progress as he goes along. At the moment the website only has details of his HUGE loading coil. See http://rescueelectronics.com/9-Kilohertz.html .

Laurence K6VLF is also active and says VLF radio enthusiasts are not limited to listening, some are sending out signals using home built equipment. His samples here are from an experiment to find out if VLF can be used for amateur communications. It was done in the Sierra Nevada Mountains in California. The transmitter sent out an intermittent CW (continuous wave) signal at one mile from the receiver, then again at two miles. The frequency used was 1.8 Kilohertz, well within the VLF range.
  • Sample 1 (650 Kb) Low power (one-half watt) at one mile
  • Sample 2 (650 Kb) High power (100 watts) at one mile
  • Sample 3 (650 Kb) High power (100 watts) at two miles

More about this experiment can found here: VLF Transmitting Experiment #2

http://www.home.pon.net/785/equipment/transmitting/VLF_transmit_2.htm




EXPERIMENTS IN POLAND

Marcin SQ2BXI has sent me this message today (April 17th 2010):
 
In last night we have VLF eksperiment in 9,6kHz in SP2KDS Club.Club signal copied Jacek SQ5BPF -distance 290km.
Movie tranmiter: http://www.youtube.com/watch?v=2sn6AmpkwlU&feature=player_embedded
and Polish page: http://www.sp2kds.pl/136khz/298-pierwsze-proby-nadajnika-w-pamie-marzycieli.html

Next experiments will soon have to 8.970kHz...
73! Marcin SQ2BXI


HOW FAR CAN YOU GET WITH INDUCTION ONLY BELOW 9kHz?

This was a question I put to the LF Reflector people recently. An interesting reply was received from Jim Moritz M0BMU who did the maths and gave this response:

Dear Roger, LF Group,

It is interesting to try to work out what might be possible by induction...

First, how much magnetic field is needed for reception? Assuming we can make a receiver where external noise dominates, Paul Nicholson gave a typical figure of magnetic flux density of 30fT/sqrt(Hz) for the noise level. Assuming we use QRSS100 with about 0.01Hz BW, and 6dB SNR, we need to generate about 6 femto-teslas of magnetic flux density at the receiver to get a readable signal.

Now the transmitter - assume a "largish" loop means 10m diameter, and it is a single turn with resistance of 0.1R, or a multi-turn loop with proportionately less current. With 100W, the single-turn loop current would be about 32A when matched. My old physics textbook says that the magnetic field on the axis of a circular loop, at a distance that is large compared to the loop diameter, is

B = (mu0*r^2*n*I )/  2d^3

with mu0 = 4pi*10e-7, r = 5m, n =1, I = 32A, and B = 6*10e-15 T, d = distance in m

Rearranging to find d gives

d = cube-root-of( (mu0*r^2*n*I)/2B ) = 4.4km

So quite a long distance (have I got it right?!), making some quite optimistic assumptions. You could get a bit more by reducing the loop resistance, or increasing the loop size, power etc., but the cube-root means it would be hard to make a big increase in range. To reach DF6NM's 12km, you would need to increase the loop current to about 650A! The presence of the ground would probably have some effect. As has previously been pointed out, conductors such as mains cables or telecomms lines near the transmitter would have significant currents induced in them, and these could act as transmission lines carrying the signal much longer distances, but this might be thought of as "cheating"!

Cheers, Jim Moritz
73 de M0BMU

Earth-mode (through the ground conduction) and induction communication (mutually coupled coils) have an inverse cubed attenuation with distance. Think about this: I reached 0.3km with earth mode for an audible CW signal with around 4W RF and a simple 5m base receiver and 10m base transmitter. To double this range, all other things being equal, means increasing power by 18dB to 250W. To double range again means raising the power to kWs. Conversely, improving the detectable sensitivity threshold by 18dB (increasing the electrode spacings at each end, using WSPR or QRSS, etc) reduces in power needed for a given range dramatically: my 4W signal could be detected at 0.6kms or a just a 63mW signal could be detected by earth mode at 0.3km. In reality, especially in urban areas, water pipes and cabling may help "propagation" and achievable ranges may be greater. DX is relative, especially with conduction and induction at VLF.



NATURAL BACKGROUND NOISE BELOW 9KHZ

The main noise sources at 9kHz and below are man-made: harmonics of mains and other switching devices in the home and industrial places. The natural noise is primarily related to thunderstorm activity which can produce whistlers and tweeks at audible frequencies. Less common is auroral chorus. A very beautiful recording of chorus was made recently by Paul Nicholson: it sounds like birds in a forest at dawn, but the sounds are all generated by auroral electromagnetic activity.





SOME READING MATERIAL (from the late G0AKN's article)


Bishop, Leon 'The Wireless Operators Pocketbook of Information and Diagrams' ,
Bubier Publishing Co. 1911.

Fahie, J.J 'A History of Wireless Telegraphy 1838 - 1899'. William Blackwood and Sons. 1901. pp 1-5, 130 - 176.

Rabson (& Gibson and Gill) 'Cave Radio and Electronics Group' Journal 33, Sept. 1998

Hardy, James K. 'Electronics Communications Technology'. Prentice / Hall International Inc. 1986 p. 331

IEEE Transactions on Communication Vol. Com-22, No.4, April 1974
'Early Development of the Project Sanguine Radiating System' B.E.Keiser

Meulstee, Louis 'Earth Current Signalling. The History of the Power Buzzer'. Journal of
the Royal Signals, Spring 1988.

Stanley, Rupert 'Textbook on Wireless Telegraphy', Vol. 2. Wireless Press. 1919.

Kendall, G.P 'Earth Wireless, Some Notes on the Power Buzzer'. Vol. IX, Wireless World. 1921. pp 409 - 411.

QST Magazine. 'Experimenter's Section' April to October inclusive. 1942.

Bradley, C.R. 'Communications Through The Ground' Practical Wireless May 1964.
'Improved Communications Through The Ground' Practical Wireless February 1965.

Lapthorn, R. 'Radio communications at frequencies below 10kHz'
Radio Communication April 1975

Pickworth, G. 'Earth Current Signalling' Electronics Today International
February,March, April, June 1990.

VLF Earth Loop Antennas Electronics Today International
(Parts 1 and 2) April, May 1991

LF Experimenter's Source Book (2nd. Edition)
from Radio Society of Great Britain
Cranborne Road
Potters Bar
Herts EN6 3JE
ċ
Roger Lapthorn,
Jun 29, 2009, 5:58 AM
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