VLF Earth Mode

Before my 2013 stroke, I enjoyed experimenting with VLF earth-mode, which anyone can enjoy. 

In the UK OFCOM is not interested in licencing this (and taking your money!), so anyone may make an earth-mode beacon. 

For the TX PA a low cost audio IC was used. It produced 4-5W.

Years ago I kept a blog of my exploits. I hope you can get some ideas here.

See https://sites.google.com/site/sub9khz/vlf-using-earth-mode/g3xbm-earth-mode-blog .

VLF RX loop

This was the RX VLF loop antenna I used for my earth-mode tests when I was fit. It was tuned to the RX frequency that was usually about 8-9kHz. The best orientation was with the loop  on the ground. The pre-amp in the blue box was tuned to the RX frequency.

As I recall, it was about 30 turns of 0.2mm PVC covered wire.

It is still in the back of the garage, I think. It is many years since I did any tests at VLF.

Amateur VLF

Amateur operation at VLF is very different from commercial VLF. In order to be detectable with "back garden" antennas and amateur powers, very high stability is needed and very long integration times. The latter may be hours or even days!  

Some years ago I was quite active on amateur VLF. On TX I experimented with 5W earth-mode and on radiated VLF I concentrated on RX and copied several Europeans below 10kHz. The photo shows G3XIZ (45km) although I regularly spotted German stations at far greater range.

Antennas were an 80m loop or my earth-electrode "antenna" in the ground at home and a portable multi-turned tuned loop or earth electrodes in the ground out portable. Out portable, the loop on the ground was the most successful.

Amateur VLF DX in 2011

 It’s some years since I did experiments at VLF. This was my first DX on 8.97kHz VLF.

VLF earth-mode experiments 2010

Way back in 2010 (when I was fitter!) I used to enjoy going out to see how far away I could detect my VLF earth-mode beacon running 5W. The furthermost I got was 6km, but much further would have been possible with more power and a larger baseline. Indeed, if the power is increased and the baseline larger I know of one station that has been received 100s of kilometers away. The RX station was able to detect the radiated component that was probably just microwatts. Earth-electrode "antennas" have been used successfully on  radiated tests at even lower frequencies with remarkable ranges being covered.

VLF upconverter

Many people want to take a peek at what is on VLF. The problem is that many receivers do not tune that low. One answer is an upconverter so that VLF is translated to a frequency covered by a conventional receiver. 

For amateur VLF signals, this is extremely unlikely to be useful as VLF amateur signals need great frequency accuracy, extremely narrow bandwidths and long integration periods measured in hours or days. 

For VLF utility stations this upconverter will be useful.

See https://sites.google.com/view/g3xbm4/home/vlf/vlf-converter

2011 VLF memories

 Before my stroke I really enjoyed experimenting with both ends of the spectrum. I quite enjoyed seeing how far I could get on VLF earth-mode through the ground. This was a Facebook memory from 2011.

VLF earth-mode TX

Looking back over some of my old photos, I came across this photo of my 5W earth-mode VLF transmitter, that was last used over 10 years ago. 

The 3C90 toroid on the left is to match the low impedance output from the TDA2003 to the earth-electrode "antenna" in the ground. In the centre is the TDA2003 audio amplifier. On the right is the keyer IC that can produce QRSS or CW.

It would be good to do some more experiments in the future, if my health allows.

Amateur radio below 9kHz

 

This was 2011. It is a long time since I did experiments at sub-9kHz

Sub 9 kHz DX

Some years ago, I was quite keen on amateur radio below 9 kHz. I well remember people saying it was a waste of time and nobody would get beyond the garden fence. How wrong they were!! Some quite remarkable distances have been spanned. 

Although for radiated DX below 9 kHz very big antennas are needed for TX, on RX some tiny antennas can work perfectly well such as an E field probe which is tiny. What is needed is very high stability and very narrow bandwidths, usually achieved by locking to a VLF MSK signal or GPS. Some years ago DJ8WX was spotted by locking to a VLF MSK signal (see photo). All this was possible with free software. Sometimes it is necessary for signals to be integrated for hours or even days.

It is some years since I have experimented at real VLF.

Sub 9kHz amateur radio

At one time I was very active monitoring amateur radio below 10 kHz. Stations from all over Europe were decoded. I also used to regularly run a website dedicated to amateur experiments at the very low frequencies. Some remarkable distances were spanned. 

To TX, very big antennas are needed. For RX an E-field probe, which is tiny, is very effective. Extremely accurate frequency control is essential. This is usually achieved by GPS locking or locking to a VLF MSK signal, which is what I did. Bandwidths are measured in uHz. Timescales are measured in hours or even days! Casual listening is extremely unlikely to result in success, except perhaps by earth-mode over much shorter ranges. 

Since my 2013 stroke, I have not been active below 10 kHz. Experiments continue and keen amateurs are still knocking on the boundaries and achieving what many thought was impossible.

The photo shows my reception of DK7FC in 2011. In more recent times he has been testing on ever lower frequencies and with earth-electrode antennas.

Software VLF RX

This very simple software RX by SM6LKM was found about 10 years ago. I think it has been developed further by others.

VLF E-field probe?

 

This photo was taken some years ago. I think it shows my VLF E-field probe.  It is just possible it was the VLF loop pre-amp as they looked very similar.

5.17kHz loading coil

This was a photo from 5 years ago of the 5.17kHz loading coil at DF6NM. Some remarkable distances have been spanned by amateurs at these VLF frequencies. 

G3XIZ sub 10kHz

This photo was taken some years ago and shows the signal from G3XIZ on VLF at 45km. Notice the timescales - hours!! 

French amateur success on 8.27kHz

F5VLB has been received in Todmorden, UK by Paul Nicholson. Jean-Marie was using a 75m base earth-electrode antenna. Paul was integrating the signal which had to remain stable for a very long time (days). This is, I am sure, the first reception of a French amateur outside France below 10kHz.  Huge congratulations to both stations. This is a result of hard work by both.

UPDATE 2230z:  Apparently the power has been increased a bit and he is being copied in Italy too!

VLF beacon TX

This was the beacon TX I built for earth-mode tests at 8-9kHz. It can send either CW or QRSS at about 5W. It is some years since it has been used. A range of 6km was the best I achieved by utilities assisted earth-mode. 

I don't think it has ever been used at this QTH and we moved here in 2013! My stroke rather stopped field work sadly.  I would like to do more, but fear this will not be possible. I am sure much further would be achievable. 

Interesting that earth-electrodes of sufficient size combined with plenty of power have been used in radiated sub-10kHz tests.

SAQ transmission - tomorrow

The historic 17.2kHz VLF alternator CW TX that is a World Heritage Site and almost 100 years old is on the air tomorrow, December 24th with a special message. They will QSL. 

I am a proud possessor of a rare QSL card from them many years ago. I think this was with my VLF converter and loop antenna. I thought this converter was on my website, but it seems to be missing. I shall add it later. For now, see this page.

There is a very good software RX on my video channel. This with a simple antenna and small preamp connected to the PC sound card is all you need. 

The whole thing is being live streamed on YouTube I believe.

See https://alexander.n.se/en/ .

See also the software VLF receiver by SM6LKM on my video channel at https://www.youtube.com/watch?v=TDxRhQYg7lQ .

UPDATE 1635z: The VLF up-converter should now be available via my G3XBM website (added today).

Sub 9kHz amateur radio

In 2010 I managed to see DK7FC on 8.970kHz using my earth-electrode antenna in the ground. Notice this took hours! Just a faint line. After this, several signals across Europe were copied. Note that each marker is 0.1Hz!! Very narrow bandwidths, very good stability and long integration times are essential.

Earth-mode VLF

In days past, I managed a fair bit of success with VLF earth-mode. This is a form of VLF communication that many can enjoy. Gear can be simple and low power.

See https://sites.google.com/site/sub9khz/vlf-using-earth-mode/g3xbm-earth-mode-blog .

https://drive.google.com/file/d/1-ytg1yoyiezffsfSqdL2kWZW_Fx3sbru/view?usp=sharing .