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.

474.2kHz WSPR results - 15m earth-electrode baseline

I left 474.2kHz WSPR running overnight using the 15m baseline earth-electrode running vaguely E-W. Results were encouraging. Don't anyone say they can't erect an antenna for 474.2kHz! If even THIS works, almost anything is possible.

474.2kHz UNIQUE WSPR spots in last 24 hrs on
15m baseline earth-electrode "antenna"

Some stations are actually stronger on the earth-electrodes than on the conventional "wire in the air". Best DX 701km with an ERP around 5mW MAX and no conventional antenna is not at all bad. I am sure a proper Marconi antenna would be better but the earth-electrode ground "antenna" is a good compromise system when options are limited. It is totally invisible too - VERY neighbour friendly.

On the receive side, 10 unique stations copied in 4 countries. Not bad for a less than 24 hr period.

474.2kHz UNIQUE WSPR spots in last 24 hrs on 
15m earth-electrode baseline on receive

Earth-electrode antenna for 472kHz in the new garden - not too brilliant

After trying a number of different orientations of earth-electrode pairs in my garden, I have come to the conclusion that this antenna structure does not work very well here in the new QTH. I am a little surprised as the earth-electrode antenna worked well just 350m away at the old QTH. Whatever orientation I try I seem to be always in the -22 to -28dB S/N region with G6AVK 78km away.

Why is it not so good? Well, the most likely answer is that the effective distance between the far and near ground rod electrodes is smaller, even with a similar physical separation. This could be because of buried water pipes and utilities criss-crossing the garden, although I wasn't aware of any, or different soil/rock conditions, although the chalk layer is about as far down here as at the old QTH and the soil is a similar alkaline sort. The fact that the 8.97kHz earth-mode results were so poor last week rather hinted at a problem that was not present at the old QTH.
 
I haven't quite exhausted every layout possible in  my strange shaped back garden, so there are more things to try with earth-electrodes, but it is looking like I shall have to erect a short Marconi or a fully in the air loop antenna to get better ERP on 472kHz. On my previous tests at the old QTH, a full in the air loop with 1mm diameter wire and an enclosed area of around 80m sq was around 8dB better than the earth-electrode antenna, but far more critical to tune and match because of the hi-Q. If my earth-electrode antenna is several dB down on the performance of the same structure at the old QTH then I could be expecting >10dB improvement or even more.

Half the fun is the testing and finding out what does and does not work.  The coming week we have visitors staying, so not too much time to experiment. I shall have to stick to WSPRing on 20 and 10m.

New VLF tests from Germany

News from Germany of an upcoming VLF test at 8.970kHz using earth electrodes as the TX antenna with an ultra-stable Spectrum Lab derived signal.

Hello Group,

 

We are planning some VLF-activity at 8970Hz during a meeting of  electronic hobbyists nearby  Kassel / Germany (JO40vr) on this weekend.  The plan is to run a VLF-PA between some ground electrodes. Due to other activities we have no exact time plan, when to start. Depending on internet access i will inform you about the details. 

 

Thanks for looking for our signal in advance.

 

73s

Eike DL3IKE

Earth-electrode antenna on 40m

This evening I have been trying my stealth antenna (20m separated earth-electrodes, wire in the grass!) on 40m again and getting plenty of WSPR spots. I did try to match it on 160m earlier but couldn't get it below about 3:1 using the Elecraft T1 auto-ATU. Spots from 6 countries in an hour (LA, DL, F, EI, GM, G) with strongest reports from Cornwall (-3dB S/N) which is in the line of the wires/loop.

WSPR spots received using 20m spaced earth-electrode antenna with NOTHING in the air.
 

Earlier today I had a visit from Ted G4NUA, so I showed him my 137kHz antenna, "Where is it?" he said. Exactly - the wire runs back to the house from the far earth rod IN the grass and it is all but invisible!

Earth-electrode antenna on 80m

This evening I have been using the 20m baseline earth-electrode antenna on 80m. From the shack (upstairs) there is a 20m coax down to the back of the garage where it picks up the earth electrode wires. On 160m the match is poor but on 80m a near perfect 1:1 match, so no radiation from the coax.

On receive there are plenty of signals visible and decoding on WSPR and on TX it seems to be getting out pretty well with 1W RF from the FT817.  I am not sure of the ERP on 80m, certainly higher than on 630m (472kHz), but it does appear to be quite effective.

Tomorrow evening I'll match the earth-electrode antenna with the Elecraft T1 auto-ATU and see how it performs on 160m. I'll put the ATU right at the earth-electrode end of the coax so that we'll see the radiation from the earth-electrodes and not the feeder.

Back on the earth-electrode antenna on 472kHz

The red dots show where the wire to my far earth rod goes - under the snow!

This afternoon I've installed a coax cable from my operating shack down to the back of the garage where I do my radio building and where I can connect to the earth-electrode antenna running down the back garden. Now I have my 472kHz transverter in the garage too so it can connect directly into the earth-electrode antenna without any matching. Even with 8cm of snow on the ground and nothing of the antenna visible above the snow line (!) this antenna is still radiating a decent signal with reports already this afternoon from G3ZJO (-22dB S/N) and G3XDV (-12dB S/N) at good range. I find it truly amazing this system works at all.

I am signing G3XBM/1 on the WSPR database to distinguish my signal from that transmitted using a Marconi where I use G3XBM.  I hope no-one minds me using this suffix for a short period, but it is very much in the interests of good research. The signal level with G3XDV at 61km is about 8dB weaker on the earth-electrode antenna than on the vertical Marconi.

Earth electrode antenna conclusions (472kHz)

With some further tests today I am now able to arrive at some conclusions from my experiments with an earth electrode antenna at 472kHz. Many people including Jim M0BMU and Rik OR7T have been particularly helpful in analysing the data.

My current 472kHz earth electrode "antenna" - can you see it in the grass?

These are my conclusions:

1. The earth-electrode antenna at 472kHz (2 earth rods in the soil 15-20m apart fed from the TX output) behaves like an H-field loop transmitting antenna.
2. It has directivity, with strongest signals in the line of the loop and weakest signals at right angles to it.
3. It works as an effective RX antenna too.
4. In my environment the loop looks like about 50-60 ohms resistive, so a good match to my transverter directly without matching.
5. The structure works because much of the return current flows deep within the soil and rock beneath the earth-electrode antenna. In my case Rik OR7T calculated that the loop area in the ground is effectively 290m sq with a radiation resistance of 0.017 ohm and a loss resistance of 66 ohms.This is a BIG loop!
6. Performance compared with my 9m high top loaded Marconi antenna averages only around 8dB down, not a bad figure at all, even with the connecting wire on the ground and not elevated at all.
7. Where no other antenna option is available, the earth-electrode antenna is well worth trying both on 472kHz and on 136kHz both for RX and TX. Although it works well here, your geology may be different and results not the same.

These last few days have been most interesting and, with the help of many people - listeners giving me WSPR reports, advice from others on the Internet forums, suggestions by email - I have been able to do some quite useful science. Thank you one and all.

472kHz earth electrode antenna: nothing in the air

Today, I took my experiments with an earth electrode TX antenna for 472kHz to new levels by placing the connecting wires on the grass i.e. not elevated at all.  The theory developing is that the earth electrode antenna works by forming a buried loop in the ground with the earth return path being in the soil and rock beneath the structure. If this is so, then even with the wire sitting on the grass there should still be a loop within the ground, so some radiation from it. Results this afternoon prove this is indeed the case. The following are the results with a 20m baseline between the far earth rod and the copper pipe ground at the home end and with the connecting wire just laying on the grass lawn.

472kHz WSPR reports with earth electrode antenna with wire on the lawn

How far down is my 472kHz earth electrode antenna on a Marconi?

This evening I have been noting my WSPR S/N reports from stations across the country and nearer Europe using my 9m long Marconi antenna and comparing these with the reports last night when I was using just the 15m baseline earth-electrode "antenna". I crudely plotted the "improvement factor" in dB on a polar plot. Each dot represents a station reporting my signal with the dB improvement over the earth-electrode antenna plotted on a 0-20dB scale out from the centre.

Although in some directions the difference is very little, in other directions the reports are up to 14dB better on the (omni-directional) Marconi.

Stations with dB improvement using the Marconi antenna

M0BMU 10dB
G0KTN 6dB
G3ZJO 5dB
G3WCB 10dB
DL-SWL 2dB
G4HJW 6dB
M1GEO 14dB
G7NKS 6dB
M0LMH 11dB
G0MQW 10dB
G0MQW 10dB

My conclusion is that the earth electrode antenna is behaving somewhat like a loop with directionality along the line of the earth-electrode baseline and a null off the sides. With stations receiving me off the sides there is most improvement with the Marconi, and less difference with stations end-on who were getting a reasonable signal with the earth-electrode antenna.

CONCLUSION: the simple, stealth, earth-electrode antenna is a VERY useful antenna on 472kHz as long as one is prepared to accept a 2-14dB loss compared with a reasonable Marconi.

A Marconi antenna on 472kHz

So that I can better quantify the performance of my various earth electrode "antennas" I have today erected a 9m long top loaded Marconi vertical for 472kHz. Initial antenna current measurements suggest the ERP is up around 10dB to around 100mW. My plan is to run this overnight again and then tomorrow compare the signal reports against those with my smaller compromise Marconi and my two earth electrode antenna configurations.

Even more fascinating 472kHz experiment

Following on from yesterday's tests, today I started a further test using an earth electrode "antenna" on 472kHz WSPR.

This time I used 2 ground rods in the soil separated by 15m of wire (fed directly from the transverter output at 50 ohms) and powered entirely from a battery supply - PC, FT817, transverter, SignaLink interface - so that there was no connection whatsoever to the house mains earth or copper pipes in the house. The power out would have been slightly lower (lower supply voltage) and the baseline 25% shorter.

472kHz earth electrode "antenna" system in garden

So far, results are almost identical to those obtained yesterday when one side of the earth electrode system was connected to the copper pipes in the home on one end.

My best DX WSPR report this evening with 10W RF out from the transverter into the 15m separated electrodes is G0KTN at 210km. ERP is in the low mW region at best. On RX DJ8WX has been copied at 643km.

Although a large Marconi antenna will be far better, this set-up certainly works and gives highly credible results. Considering just how simple this is I hope others experiment with the earth electrode "non antenna" and see how they get on.

UPDATE: Best DX report of my few mW ERP signal with 15m spaced earth electrodes was from DL-SWL at 701km. I am copying lots of signals including SM6DHZ and DK7FC even after breakfast time. Amazing.

Analysis of 472kHz antenna tests today

With several hundred WSPR spots of my QRP signal received today on 472kHz, I have tried to do a crude analysis of the difference in performance between my short (1/100 wavelength long) Marconi and my earth electrode (ground) antenna. I did this using MS Excel. Now I have forgotten most of the things I knew about Excel, so this is basic stuff here!

I plotted the maximum and minimum signal reports for each type of antenna for a number of different reporting stations and plotted a graph showing the difference and the angle the station is from me to see if there was a clear directionality in the earth electrode system.

Analysis of signal levels with short Marconi and Earth Electrode antenna at 472kHz

Conclusion? I'm not sure, although the difference between the 2 antennas varies from as little as 0.5dB (PA3ABK) up to 16dB (M1GEO) with an average additional loss of around 7dB. Can you see any indication of directivity in the earth electrode antenna? I am assuming the Marconi is omni-directional, which of course may not be the case.

Not bad for an antenna that is invisible to the neighbours and still is capable of getting reports (so far) to 701km away with a few milliwatts ERP.

Earth electrode TX/RX antenna at 472kHz

Signals received on 472kHz WSPR using the earth electrode "antenna"

This afternoon I've been experimenting with my 20m spaced earth electrode system (used at 8.97kHz VLF), but this time on 472kHz WSPR. One electrode is an earth rod at the bottom of the garden and the other is a connection to the copper pipes in the home. Although I need to analyse results more carefully after an overnight run, the system certainly works with spots of my TX already received across England and from Holland. G4HJW 9km away is as nearly strong on the earth electrode system as on my vertical Marconi.

UPDATE 1715gmt: just been spotted by DL-SWL at 701km!!!

I honestly do not understand why this system - with wire no higher than 1.5m in the air running along the fence between the earth rods - works as well as it does. This is a short video showing the system in operation.

The ERP with the earth electrode system cannot be more than around 5mW which makes the performance all the more remarkable.

Some of the TX reports this afternoon with the 472kHz earth electrode system

A return to earth-mode VLF experiments

This afternoon I installed a more permanent earth-mode ground system to use in forthcoming tests at VLF through to 500kHz. Instead of bringing the 2 earth connections into my upstairs shack, as I had done previously, I have now installed a couple of grounds and wires that come into my "designing" shack downstairs. This means I can now run a lot more tests using the test equipment at my disposal. It also means I do not tie up equipment in my "operating" shack upstairs when doing earth mode beaconing.

The diagram shows the current arrangement of the grounds and wire. At its highest point the wire is 1.5m above ground, running along the back garden fence. It is invisible.

Tomorrow I hope to get the ULF/VLF earth-mode beacon TX on-air initially on 8.97kHz and 1.147kHz in QRSS3 and QRSS30 and carry out my usual reception test at a point 1.6km from home where the signal is usually strong. Subject to satisfactory results with the new TX "antenna" I then intend to do a series of RX tests using new equipment out to around 10km from home.

8.971kHz VLF earthmode test

30t loop on the ground feeding E-field probe

An 8.971kHz earth mode (VLF through the ground) test was conducted today at 1.6km and 3.5km from home. The TX was 5W QRSS3 into 20m spaced baseline earth electrodes: one a 1m copper rod at the
far end of the garden and the other end grounded to my copper hot water tank in the house.

At the RX end I was using either (a) a 30t tuned loop feeding either the PA0RDT or G3XBM tuned E-field probe, and (b) the same E-field probes but fed with a 19 inch whip instead of the loop.

Good signals were received at both locations with the loop into both probes but there was no detectable signal when receiving on the 19 inch whip into the EFPs.

It was a struggle to see the difference between the PA0RDT and G3XBM E-field probe/preamps, but I think results with my tuned drain design may have been marginally better on this test.

LF tests with the earth electrode "antenna"

Following the great success on 160m with the 20m spaced earth electrodes yesterday, I fired up the WSPR transverter into the same "antenna" today on 137.5kHz. Although I managed to decode G8IMR at 188km several times, no reports of my signal were received. This ties up with tests last year which suggested the earth electrode system was around 8dB down on my 80sq m vertical wire loop. With results on 137.5kHz hard to get with 500uW ERP it was perhaps not surprising that no-one managed to decode me on the earth electrodes.

I now have a choice on 137kHz: either re-erect the wire loop, but double the wire thickness when I do so, or change to a Marconi vertical with a large loading coil. The thicker loop will increase ERP by up to 6dB but I suspect more is to be had with the vertical. It would be daft of me not to give the Marconi a try both on 137.5kHz and on 500kHz. Even with my limited space I can still manage around 8m of vertical with around 20m of top section.

Amazing evening on 160m ...without an antenna

160m WSPR reports - using 5W to 20m spaced earth electrodes

What an amazing evening: tonight I let my 5W WSPR beacon run with my VLF earth electrodes (20m separation with a low wire feed) as the "antenna" i.e. no conventional antenna in the air at all. Just look at these results! 6 countries and best DX 896km to the Shetland Is. If the earth electrodes are acting as a "loop in the ground" then the Shetlands are in the wrong direction i.e. in the null of the loop.

Sunday I intend to try 137kHz with the earth electrodes as I now have some 6dB more power than the last time this was attempted.

Earth electrode "antenna" on HF

Today I had to prune the tree to which my 80m sq wire loop is attached, so the loop had to come down for a while. Instead I connected up my 20m spaced earth electrode pair "antenna" with the connecting wire about 1.5m off the ground coming back along the garden fence. This is the antenna I use on VLF earth mode tests with the best DX reception of my signal being 6km away when using 5W at 8.76kHz.

I have been amazed how well this works on 160-40m this afternoon. This is the log this evening on 160m with 5W WSPR - best DX report so far from OZ7IT at 853km. On 40m I reached over 2000km with a report from the north of Norway.

6km DX on 17.52kHz earth mode

My 5W QRP signal at 17.52kHz is clearly visible at 6km

Last evening I continued the earth mode tests at 17.52kHz by going out to the test site 6km from home and looking for the signal with a variety of antennas in QRSS3 and with an interrupted long carrier transmission.

No copy was achieved using QRSS3 and Spectran. However, using a continuous carrier with a 2 minute ID break I got extremely good copy (about 6dB S/N) with Spectrum Lab in 37mHz bandwidth with the horizontal 30t loop but no copy on the earth electrode antenna parallel to the road. Moving the loop 10m away from the road resulted in no copy, as did mounting the loop vertically or a few metres above the ground.

It would appear that at 17.52kHz it is easier to detect the signal at distance with a loop than with an earth electrode antenna whereas at 1.095 and 8.760kHz either scheme works. Perhaps someone who understands the theory will be able to explain this.

My next test is to repeat these tests at 137kHz to see to what extent 137kHz is aided locally by utilities assisted earth mode. At the test site 6km away I can see how strong the signal is with tight coupling into the ground at the roadside, and with an E-field probe some distance away from the road.