VLF earth-mode tests in 2011

 

As part of my experiments with VLF earth-mode was a test in 2011 at just over 17kHz using my 20m separated earth-electrode "antenna" in the ground.

1kHz earth-mode 2011

 

The photo shows my 2011 experiments with 5W at just over 1kHz. A range from home of 6km was made.

VLF earth-mode beacon

 

Some years ago I really enjoyed experimenting with earth-mode VLF at 5W. I built a beacon TX and went out in the Fens trying to receive it. My best DX was about 6km, although I remain convinced much further would have been possible with more power and a bigger TX baseline.

Of course with hundreds of watts and a bigger earth-electrode baseline some radiation is likely, so hundreds of km becomes possible. With earth-mode most of the signal is conducted through the ground.

I had to stop when I had my stroke, which stopped me doing all sorts of field experiments. These days I hope others are carrying on where I stopped. Meanwhile I experiment, on something else, at home.

VLF transmitter

 

Looking through some old photos I came across this one of my VLF transmitter that was used for earth-mode tests though the ground. 

It produced about 5W and my best DX (before my stroke intervened!) was about 6km. Much further would have been possible.

Since my stroke, I have been unable to continue my VLF tests. It is still on my shelf.

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 .

Earth-mode tests in 2011

One of my Facebook memories was an experiment in 2011 at a distance of 6km on 1095Hz using 5W.  Later I achieved even better results.

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

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.

Earth-mode paper

 Someone asked for access to this file. It is now open so if you have this link you should be able to read it. It was sent to me some years ago.

See https://drive.google.com/file/d/16vtYNznORclXJTfpaT-RC7Z3IV8RKqyi/view?usp=sharing .

Earth-mode VLF

Earth-mode is a form of VLF communication that is open to all. With 5W I managed to cover 6km, although far further should be possible even with the same gear. I have updated my webpage to include a link to my earth-mode blog showing my experiments some years ago. 

My understanding is this does not require a UK licence, but check with OFCOM as I cannot give legal advice.

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

Earth-mode VLF blog

On my old website I have a blog about my experiments many years ago with VLF "earth-mode"  communications using 5W. 

As the page is very old, I cannot guarantee links work. The links on the left of that page are very old especially and should not be used as this was my old website that is not maintained.

Earth-mode is a form of VLF experimentation that does not need high power or big antennas. It is at the frontier and is open to all. 

My understanding is no licences are needed for this form of communications based on conversations with OFCOM many years ago. This is not a legal statement, just my interpretation. 

For radiated VLF communications I think those in the UK need an NoV, whereas in many countries below 8.3kHz is a free for all. As very special techniques are needed for amateur VLF radiated reception, I think the chances of being intercepted are very small.

See https://sites.google.com/site/g3xbmqrp/Home/earthmode . 

Earth-mode VLF

Yesterday, I mentioned amateur VLF experiments below 9kHz. A very accessible introduction is earth-mode communications, especially utilities assisted earth mode. Using the latter mode, 6km has been spanned,  with just 5W, although much further should be possible. With much higher power and larger baselines at the TX end, I expect the small radiated power will be detectable hundreds of km away, although this is not going to be earth-mode.

An example of a typical earth-mode VLF transmitter is shown at the link.

CIA 1960 report on earth current signalling

An amateur in Germany, DL3IKE, found this recently:

https://www.cia.gov/library/readingroom/docs/CIA-RDP78-03424A000400090001-9.pdf

VLF (8.97kHz) TX

8.97kHz 5W TX

Before my stroke in 2013 I did a fair bit of experimentation at VLF, successfully receiving quite a few European amateurs on VLF doing radiated tests. I did some "through-the-ground" utilities assisted earth-mode tests out to 6km using just a 5W transmitter. At some point I'd like to do more.

See https://sites.google.com/site/g3xbmqrp3/vlf/8-97khz-earth-mode-transmitter

Earth-mode VLF communications

Today I received a nice email from a station in The Netherlands on the subject of earth-mode communications. Apparently he had been inspired by my work and was still hoping to achieve better results. Earth-mode requires simple gear and simple test gear, but results can be unpredictable. It is an area where true experimentation is still possible. From my limited tests when I was fit (before my stroke) I am convinced there is a lot more to learn.

"Hello Roger,

How are you doing? I hope you are doing fine.

Since this is my first mail adressed to you, please let me first introduce myself.

My name Is Jan ( PE1AXM ) and I am a radio amateur since 1977 and live in the south-west part of the Netherlands, my age is 59.

My radio interests are mainly: making home made equipment.

About 1 year ago I discovered one of your articles that triggered my interest in 9kHz earth mode communication. So I started building. For Tx I use 2 earth rods, 2 meters long and separated 20 meters.Resistance between these rods is 16 Ohms.

A home made amplifier is capable of delivering 1 Amp into these earth rods.

For reception I use a small loop antenne that resonates at 9 kHz, followed by a low noise pre-amp and a PC with Spectran Plus software.

To be honest, I thought that a range of 4 km's would be an easy job, but I soon found out that this was not true.

My best dx so far is just over 1 km, but I realise that still a lot can be improved on my system.

Roger, I thank you for your stimulating articles and I hope that you will make further recovery."

VLF field test - a total failure!

Well, I did my first VLF earth-mode field test today since my brain bleed in Sept 2013. Sadly, it was a total failure. I am at a loss to explain the results.

Tuned VLF loop

I put the 5W, 8.976kHz, beacon on into the same earth electrodes used successfully on 472kHz (best DX on TX over 1000km) and went about 1.6km to a car park where I always had strong signals using a tuned loop on RX and earth-electrodes on TX from the old QTH in the same village. Nothing at all copied today - absolutely nothing. I waited in case I was in a pause between QRSS3 callsign transmissions, but no absolutely nothing at all. Not even the tiniest hint of a signal.

Deploying the VLF loop (Burwell in the background)

So I parked in the road about 0.3km from the home QTH and again nothing at all. At this point we drove home. What a dismal failure this was turning out to be. I am sure it is telling me something but I cannot work it out.  Sure enough, everything was still working at the TX end.  I am using one remote ground and the mains ground at the shack end, exactly as for 472kHz.  I did check this mains ground was grounded to real ground.

Checking Spectran on the PC - nothing !

Whatever utilities assistance I was getting before at the old QTH is not the same at this newer QTH. All very very odd. I was expecting to see something. In the past I received transmissions from the old QTH at the new QTH (about 0.3km away) using just an E-field probe on the car. From the old QTH I spanned 6km!

In summary, this VLF test was a total failure. I am at loss to explain things. Not only that, but the work has left me very exhausted. My brain is still foggy, but the results today were not due to any mistakes with the HW gear or PC Spectran settings.

I am not having much success today.

VLF field test tomorrow

Today I adjusted the turns ratio on my 8.976kHz VLF QRSS3 and 10wpm CW 5W beacon to better match my earth electrodes. At this QTH they look much greater than 50 ohms, which I measured at the "old" QTH and optimised for.

On the way I managed to blow up a TDA2003 IC, which I had to replace. The whole exercise was far more exhausting than I was expecting. It seems that after about 10-15 minutes of physical or mental effort I am done in. Before my cerebellum brain bleed everything today would have been trivial. Now trivial tasks feel like climbing mountains! Although I can see progress in my recovery there is still a long way to go. One of my aims (among many) is to be able to resume field tests as before, but time will tell if I am really up to this: it is quite hard when your brain is still foggy a lot of the time. Oddly, when sitting down at home or when driving things are fine. It is when I do something requiring real physical or mental effort that I get tired. I guess the radio work today was hard as I had not done this sort of thing for some time.

Anyway, the good news is that I hope to do a VLF field test tomorrow.  Everything is ready and tested. It will not be until late afternoon as both my wife and I are busy before then. The XYL will be there at the test site if I get really tired.  Setting up the gear will be especially tiring in my current state. The test site is not too far from home. I have soak tested the TX and it should be fine on QRSS3 using my loop and Spectran at the RX end. I shall report results tomorrow. This will be my first VLF field test in over 18 months. How I have looked forward to this. If the loop is successful I may try the E-field probe.

First (restarted) VLF earth-mode test

5W VLF beacon TX

OK, I was only testing from the shack to the lounge, but this is a start.  TX is 5W from my TDA2003 beacon.

TX frequency 8.976kHz initially with 10wpm CW, 300Hz bandwidth, sending my callsign and a dash. Nothing copied at first using a dummy load but over 70dB over noise using the earth-electrode "antenna" with no attempt to optimise match (fed via the same 3C90 step-up transformer used on 472kHz).   With no probe at all (i.e.no RX antenna) the S/N was still some 40dB i.e. very good using the TX into the earth-electrodes.

QRSS3 signal received on Spectran (0.37Hz BW)

Later with QRSS3, a 50 ohm TX dummy load, E-field probe at the RX, I got the signal at 10-20dB S/N.  At the RX end I was using my simple E-field probe into a USB soundcard into my Windows 8.1 laptop. 

E-field probe

The blue photo shows the signal at the RX. The first part shows the TX signal on the earth-electrodes and the second part (weaker) was the signal on the EFP with the TX into a dummy load.

Honestly, this has really exhausted me!

Experiments again - soon I hope

Before too long now, I hope to be able to resume driving again, following my brain bleed over a year ago.

With a bit of effort, I should then be able to resume some VLF earth-mode and 136kHz experiments, looking for my signals from home when out and about in the car, parking up at various sites in the area.

Not many months ago this would have been out of the question, but I am getting better.

One more day on 6m

For the last few days I have been patiently trying to find some TEP-Es on 6m WSPR, to no avail. Although 6m TEP (trans-equatorial propagation) is being reported in Israel, Italy, the Balearics and Morocco, here in the UK all remains quiet. I have only spotted a couple of G stations at around 70km - absolutely nothing else!

Although I shall try again tomorrow, that will probably be my last day. A pity as I was quite hoping we might get an Es opening to link up to some TEP, but it looks unlikely now that I shall be in luck.

Later this week I may return to VLF earth-mode if I can optimise my TX earth-electrode match at 8.97kHz and re set-up my RX loop. My wife will have to drive me to my usual test sites as I am not allowed to drive yet.

First 8.976kHz VLF earth-mode tests from the new QTH

This evening, I did a couple of tests on 8.976kHz earth-mode from the new QTH with my 5W beacon TX. Initially I used the far earth rod about 12m from the house paired with a mains ground and set out on my travels with my loop to my usual first test site just outside the village. This is a car park for the Devil's Dyke walk. Unfortunately the car park has been invaded by gypsies, so I decided to move on to my next test site in the village of Reach (2km). Nothing at all was copied of my beacon.

Then I returned home and used the mysterious copper rod that goes into the ground just outside my shack as the local ground and still keeping the ground rod 12m away as the "far" electrode. I think this may have at one time been an oil pipe from a central heating oil tank. I have no idea where it goes. This earth-electrode pair has launched my 472kHz WSPR signal which has been copied in Belgium and Holland, but results have been disappointing, so I was not expecting much on 8.976kHz.

Rather than travel 2km, I parked outside my old QTH about 0.35km away in the village. My 8.976kHz signals were copied, but not very strongly. I suspect that this was true earth-mode without any real assistance from utilities as I do not believe either ground rod at the TX end is coupled to utilities grounds or copper pipes going into the road.

Weak signals over a 0.35km path

Path tested this evening plotted with Google Earth

Conclusions so far are that both for VLF earth-mode work and for 472 and 136kHz radiated work I need to much improve the earth-electrode arrangement in my garden to get credible results. I need to do some sort of mapping of the garden to see where would result in a good solid connection to copper water pipes going into the road (probably at the outside copper tap) and the best place to locate the "far" electrode as far away from the house (and other houses) and buried pipes as possible.