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.

Playing with a ferrite rod at VLF

Just for amusement, but with a slight hope it might work, I tried resonating a LW ferrite rod coil (about 3.5mH) at 8.97kHz to see how it might perform as a miniature portable receiving loop in my earth-mode tests.

To test other antennas and VLF preamps, I first connect my 8.97kHz 5W transmitter into a resistive dummy load and check that I can detect the signal strongly some distance away locally (about 10m away only). The emissions from the cables are such that this gives me around 30-40dB S/N on Spectran with the usual settings on my 80cm loop. Switching over to the ferrite rod RX antenna it was hard to tell if a signal was there at all.

So, that's one experiment I'll close and report as a failure. Had it worked, even 10s of dB down, it might have made a magnetic field antenna that could have been deployed mobile. You may recall I tried /M on 8.97kHz a few months ago with my 80cm loop strapped behind the car, until someone pointed out this probably would have invalidated my car insurance and I stopped.  I had vague ideas of dropping the VLF resonated ferrite rod close to the ground behind, somehow fixed from the rear bumper.

Ho hum, another idea bites the dust.

More VLF earth mode tests

Tomorrow morning, all being well, I hope to do a further test on VLF earth mode at 8.97kHz using my new Asus X101ch netbook using Spectran software and a simpler loop preamp on RX. Initially I'll test locally to check results are as expected before venturing further with the new (simpler and smaller) RX system.

Also, I want later to try TXing with a large, single turn, horizontal loop on the ground around the garden rather than the earth electrodes. On the basis that I am coupling into the ground and utilities, a horizontal loop might be as effective at coupling as the earth electrode antenna. A straight comparison of one against the other will be worth trying.

I also want to try WSPR at VLF using both my PCs.

Mobile on 8.97kHz VLF

Route taken from A to F (about 4km)

Today I did a fascinating experiment on 8.977kHz VLF using my 5W earth mode transmitter and a mag-mounted E-field probe and laptop running Spectran in the car. Basically I did a "drive around" test to see where the signal could and could not be copied.

Signal strength on 4km run between 2 villages

A continuous carrier was transmitted and I continuously monitored the received signal in the car. The drive was from the middle of the next village (Swaffham Prior), out through to the main road, then back along the main road to Burwell, around part of the village and then back home to the TX location. The signal was visible in Swaffham Prior at 5-10dB S/N, then disappears and returns on approaching Burwell where it is up to 40dB/S/N in 0.18Hz bandwidth. Within Burwell it is almost solid copy. The red timing ticks are every 30 seconds.

What I am detecting (I think) is the local E-field from the VLF signal in the ground, no doubt aided by local utilities. What puzzles me is why there is NO copy in between the 2 villages when there are, I think, pipes and cables in the road.

In the coming days this test is worth repeating locally in other directions and further afield. Fascinating to think a 5W VLF signal injected into the ground can be copied on a 19 inch whip on the car roof like this.

VLF DX radiated test results

My days long, continuous carrier test with G3WCD (32km) and G3ZJO (around 50km) around 8.977188kHz ended yesterday. I was using my 20m spaced earth electrodes with 5W out of the PA. The test was to see if anything at all could be detected well beyond the 6km I can repeatably obtain with QRSS3 earth-mode (through the ground) communications.  Despite the hint of a signal a couple of times on the G3WCD 45uHz and 22uHz grabbers, these proved to be false signals and nothing was detected.

Using Spectrum Lab, locked to a VLF MSK signal I am able to measure my TX frequency with VERY great accuracy, in fact to an accuracy of less than 1mHz. What this showed up was that my crystal controlled TX drifted (very slightly by HF VFO standards) about 13mHz over the 4 days of the test. Starting frequency was around 8.977177kHz and the final frequency 8.977190kHz. With shack temperature variations it may have moved slightly higher or lower too.

When the RX stations are looking for a very very weak signal in a bandwidth of 22uHz this means the signal is only "within band" for the FFT software to analyse for a brief period before drifting out of the measuring "bucket".  To have ANY chance it will be essential for me to lock the TX frequency so that it stays within a few uHz over a period of days. This could be done using a GPS reference signal or using Spectrum Lab. It is the latter that I shall be trying - receiving a VLF MSK signal on one antenna as the reference, then using SL to synthesise the continous TX carrier which is transmitted on a second antenna.

In reality to get 32km on VLF with my set-up was always a "long shot", but all parties agreed it was worth trying and we have all learned a lot in the process. Experimentation is the name of the game and failure is as important as success.

It may be some time before I try the long range VLF tests again: I hope to have over 100W next time and a super-stable TX signal. Who knows, we might just succeed next time.

For information on these software packages (all free) that I use at VLF see https://sites.google.com/site/sub9khz/software .

Just maybe DX on 8.9755kHz?

Last week G3WCD, who is 32km from me, monitored my very long carrier VLF transmission to see if he could detect anything. I transmitted a continuous carrier for a day with a 1 hour break during the period. On his 45uHz bandwidth VLF grabber he noticed a signal (me?) very close to my stated frequency that disappeared the day after, when I was not transmitting. So, starting late tonight, I am repeating the test with an even longer continuous transmission (days if need be) to see if the carrier re-appears on his screen. Should the signal appear, I will drop carrier for a day or so and then re-key the TX to see if the signal re-appears.  At this distance I would be very surprised if anything would be detectable, but this is certainly worth this second, longer, try. Chris G3WCD has a VLF grabber at http://g3wcd.bplaced.net/.

32km test on 8.9775kHz VLF

Tomorrow evening, Oct 16th, at 1700z I'm starting a 24 hour continuous carrier transmission on 8.9775kHz using my earth-mode system and 5W beacon TX. The carrier will be dropped for a few hours at some time (not previously disclosed) during the transmission to help later ID.

Chris G3WCD, who is 32km west of me, is trying to see if anything at all is detectable from my earth-mode set-up at that distance. We both do not realistically expect success, but with the ability to look in uHz bandwidths using Spectrum Lab it is worth a go.

If there is anyone else closer to Burwell, Cambs JO02DG85VD who wants to try looking as well, please let me know ASAP. Ideally stations in the 10-20km range.

Best DX yet on 8.97kHz earth-mode: 6km QRSS3

Today I went out to my usual test sites to check the performance of my latest VLF earth-mode system. For the first time, my RX loop and preamp could be optimally tuned in the field. At 1.6km the 8.978kHz QRSS3 beacon signal was rock solid (see first image).

5W 8.978kHz QRSS3 earth-mode signal at 1.6km (STRONG)

5W 8.978kHz QRSS3 earth-mode signal at 6.0km (10dB S/N in 0.67Hz BW)

I then moved on to a number of other locations eventually arriving at a spot 6km from the 5W TX where previously I'd only ever managed copy with a constant carrier or QRSS30 (30 second dot CW). This time the signal was about 10dB over noise in 0.67Hz bandwidth on QRSS3, my best ever result at this range (second image).

In the coming week I'll be looking for a new RX test location around 7km or further from the home QTH in the hope of increasing my through-the-ground DX record.

Earth-mode 8.97kHz VLF tests

Today I did the first tests using my new 5W 8.97kHz beacon looking for signals at my usual "close" test site 1.6km from the home QTH. Good copy on QRSS3 and even solid copy on 10wpm CW. Copy was using my 30t 80cm loop on RX although results were similar using a 5m spaced earth electrode pair. Tests at greater range over the weekend. This is a recording of the 10wpm 8.97kHz CW signal at 1.6km .

QRSS3 signal at 1.6km using a 30t 80cm loop on RX

10wpm signal at 1.6km using a 30t 80cm loop on RX

As the traces show, there are a lot of strong interfering signals around in this part of the spectrum. With an E-field probe there were lots of telemetry like signals audible which I think are being carried over the national grid overhead cables. These were about 0.5km away from the test site.

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.

VLF E-field probe design from DK7FC

DK7FC's VLF E-field probe antenna

Stefan DK7FC is well known for his experiments at VLF. Here is his circuit for the E-field probe he designed which is in use at many VLF grabbers around Europe. It is highly recommended.

VLF test by OE3GHB

OE3GHB's VLF loading coil and transmitter

OE3GHB has reported on his 8.97kHz VLF tests this weekend. He was copied by several stations in W.Europe. Gerhard's signal was clearly detected by OK2BVG, DF6NM, DK7FC and by Paul Nicholson in Todmorden. There was a trace seen by G3ZJO. At the moment my VLF system is out of action so I was unable to take a look. The picture shows Gerhard's enormous VLF loading coil. Antenna current was around 600mA and his antenna was a vertical on an 18m fibre glass pole with a 100m horizontal top wire with 600pF capacitance.

VLF test Saturday June 18th (DK7FC/P)

Tomorrow morning Stefan DK7FC/P will be testing for the first time in many months using his kite supported VLF antenna. He will be transmitting from mid Germany on 8.9700000kHz (precisely GPS locked) from around 0600z Saturday. His ERP will be in the 50-250mW region.

If you have Spectrum Laboratory (free software) and a suitable E-field probe or loop antenna then this is a great chance to see if you can detect his signals. The last time he tested he was quite a good signal in the UK and was received by several suitably equipped stations.

It is unlikely his signal will be audible, but he should be a clear trace on the SL screen with a suitably narrow bandwidth setting (4.52mHz or less). Frequency accuracy is paramount and you will need a Spectum Lab config file that "locks" onto GBZ or similar to ensure you know precisely where to look. Initial tests will be with a long carrier followed by characters in very slow DFCW or QRSS.

You do NOT need a VLF communications receiver: just a loop or E-field probe and a small audio preamp feeding the sound card of a PC. This is amateur radio "at the edge" in the same way that optical comms is .....but at the other end of the spectrum. Great fun and a nice challenge.

I shall be looking and streaming the received signals to my VLF grabber visible at https://sites.google.com/site/sub9khz/vlf-grabbers/xbm-grabber . It is also possible that G3ZJO will have his (better) VLF grabber on too at http://g3zjo.bplaced.net/ . The RSGB LF-reflector will carry updates in the event of the kite blowing away, going QRT for storms etc..

3km DX on 8.97kHz WSPR today

This morning I successfully decoded a VLF earth mode WSPR signal from G6ALB at a distance of 3km. Signal was quite strong, but for some reason the WSPR software refused to decode it (apart from once) despite clocks being reset at each end. This is my best WSPR DX reception on VLF so far. Andrew was running 40W to an earth electrode antenna. I was copying him on an earth electrode antenna although the WSPR signal was stronger later on the 80m square vertical loop in the garden.

In the afternoon I used my wife's laptop and WSPR decoded every time at -16/-17dB S/N, a very decent signal. There is a video showing the VLF WSPR set-up if you want to see it. 

DJ8WX copied again on VLF (645km)

Uwe DJ8WX is currently transmitting a long dash on 8.90022kHz and his signal was copied well on my VLF grabber overnight in a 424uHz bandwidth. Also visible is a mystery signal around 8.9701kHz that most people think is some sort of local noise source but it is very repeatable every night.

VLF Dreamer's Band video

For those interested, I've made a short video showing my current VLF receiving set-up for 8.7-9.1kHz (antenna, matching, preamp, PC) used in the recent VLF reception tests in which G3XIZ has been copied twice now (45km), DJ8WX all of yesterday (645km) and DK7FC/P twice (629km). I am not claiming it to be fully optimised, but it certainly works.

What I like is that the wire antenna and the preamp cost a few pounds, the software is free (thanks Wolf) and the results mind blowing. In the near future I will try replacing the loop and preamp with a small E-field probe.

This is the link http://www.youtube.com/watch?v=UxEAhqPFBFE

Also, G3XIZ was copied again on 9.0909kHz VLF at 45km. He was also copied by a few other UK stations including G3ZJO and M0BMU.

DJ8WX received on 8.970022kHz

DJ8WX on 8.970022kHz VLF (645km)

Overnight tonight I received a new station on VLF:  Uwe DJ8WX who is 645km east of me. Uwe was a solid signal here in JO02dg in the early hours on 8.970022kHz. His signal level dropped off during the night somewhat but he was still visible at 0500z. Spectrum Lab settings were as for the G3XIZ reception the previous night with the FFT bandwidth set to 423uHz. This is the 4th ham station now copied at VLF in 4 unique locator squares and 2 countries.

DK7FC's report on his 10th VLF test

This is an extract of the note from Stefan to the LF-reflector about his tests last weekend:

"Dear LF/VLF group and further VLF watchers :-)

After another very successful, exciting and fascinating /p VLF experiment i want, as usual, thank all the many (>=24) receiving stations who took the time to arrange a suitable antenna/receiver, PC and to watch the experiment and take some interesting captures. The transmissions took place on 2 VLF bands, 33km (8970 Hz) and 58km (5170 Hz).

So, thanks to TF3HZ, SQ5BPF, G4WGT, G3KEV, Daniele Tincani, G3WCD, G3XDV,M0BMU, G3XBM, OK2BVG, OE3GHB, G4AYT, IK1QFK, DL3ZID, F4DTL, OE5ODL, PA3CPM, PA3FNY, DL4YHF, DF6NM, DJ2LF, DD7PC (bold = 1st positive reception on VLF).

Special thanks to Halldor/TF3HZ who wasn't member of this group before but set up a very sensitive VLF receiver and even a most intersting grabber just by my email request. This is the first VLF detection between DL and TF. My signal appeared at up to 15 dB SNR in 4.5 mHz in 2404 km. This helps a bit to get some imagination how far a transatlantic detection is away.

Sorry to those who tried without success this time, like 4X1RF. The next experiment will come soon, maybe in about one month.

So, see you in the 11th experiment. :-)

Vy 73, Stefan/DK7FC'

DK7FC copied well here on 8.97kHz

After a few false starts and faulty kit, I managed good copy of Stefan DK7FC's signals on 8.97kHz this afternoon with my loop in the garden and this simple preamp into Spectrum Lab running on the PC. S/N was around 5-7dB in a 4.52mHz bandwidth. He was also copied in Iceland at over 2400kms.

DK7FC/P active on VLF this Sunday

Stefan plans to be out with his kite antenna and around 100mW ERP on the VLF bands this weekend from 0700-1630utc transmitting on 3 frequencies starting with 8.970000kHz.  Progress can be monitored on his grabber located 40km from the /P location. I am hoping to copy Stefan on 8.97kHz again as I managed it back in December.

These grabbers will show when he is active:
8.97kHz http://www.iup.uni-heidelberg.de/schaefer_vlf/DK7FC_VLF_Grabber.html .
6.47kHz/5.17kHz  http://www.iup.uni-heidelberg.de/schaefer_vlf/DK7FC_VLF_Grabber2.html