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.

Even lower!

Stefan DK7FC has been doing experiments at even lower frequencies! This was posted a few days ago. His attachment has NOT been included.

"Hello SLF freinds,

Just a note from a recent experiment at 270.1 Hz.
 
On sunday morning, 2019-05-12_10:34,+150m, i've done a carrier transmission on my ground loop antenna again. I did not expect more than, hopefully, a detectable spectrum peak in 57.6 km distance, i.e. at my tree site. The tree receiver site was listening and recording data using vlf-rx tools.
One E field antenna and two orthogonal loops were listening. The loops have been improved recently! They consist out of a single circular turn of 1.2 m diameter using 10mm diameter copper tube (about 25 mm^2). It is a closed loop, non-resonated, with an impedance matching transformer. This transformer previously had 1:100 turns. Now it (they) has 2:240 turns, i.e. two turns primary (out of 14mm^2, AWG6). This improved the sensitivity below 2 kHz significantly ( abt. 4...5 dB).
Furthermore the TX antenna length and angle has been improved, resulting in about +3 dB more signal strength on the RX site!

In a previous experiment at 270.1 Hz, some month ago, there was no result at all, not the weakest trace, despite excessive tweaking of all parameters. So the question was, will the improvements result in a detectable signal now?

Several things went wrong in that experiment. I forgot a bag containing important equipment such as the power supply for the netbook that generates the carrier signal. Also the output power was not as high as planned, just about 380 W, giving 2.2 A antenna current (I measured 64.7 V at 1 A DC). Anyway i managed to improvise so the experiment was started, but with some hours of delay which meant i higher QRN background level. Then, on the WLAN link to the tree, there were several interruptions of the stream (i'll move to 5 GHz very soon!). I even got some QRM from my battery charger for some short time periods (forgot to disable the charger remotely). So there were several factors that could have been improved or avoided. And the middle of May is not the ideal time anyway.

Well, 270.1 Hz, that's the 1110 km band! The far field begins at 177 km distance, i.e. i am clearly in the near field here. Thus, from a 'magnetic' TX antenna, we would expect that the signal is mainly detectable on the H field, i.e. the loop antennas.
The first interesting results is that this expection is actually confirmed. There is nothing detectable on the E field but the carrier S/N in the H fields is close to 10 dB in the first run. Mixing the H fields and tweaking the filters rises the carrier S/N to 10.7 dB, see attachment.

So far not really an undoubtly detection but it is a candidate for optimism! With a few less problems during the experiment there is a chance for 14 dB SNR. Also, there is quite much sideband QRM arround 300 Hz which makes 270 Hz a bit harder to work on.

73, Stefan"

More VLF experiments

Stefan DK7FC is planning more VLF tests at 17.47kHz:

"Hi VLF,

For this week, i'm planning to start with new experiments on 17.47 kHz,
where i have a (renewed) special permission to transmit.

So far the best results were a prooved carrier detection as well as a 1
character EbNaut decode by Edgar from Tasmania (VK7).

The first goal will be to determine the best time (start time and
length) on the path for this season. We have a usable path for about 2
months centered on our autun/spring time (21st SEP).

The Signal will be exported by SpecLab to simple txt files containing
the FFT data. This allows stacking, which will be required to get some
S/N at all. A reasonable stable path is essential during the
transmission time. All this will be determined by running some carrier
transmissions, a few hours per day, starting about 16 UTC.

When knowing the time to try we will attempt to transfer a 2 character
message and then even longer messages. 5 characters would be realistic i
think, with some luck and good propagation and low QRN on the RX site...

More soon.

73, Stefan"

More VLF success?

This was posted Saturday by Stefan DK7FC:

VLF,

After nearly 8 days the carrier is still on the air without an interruption, despite occasional thunderstorms :-)
It looks like the SNR is suffering by summer QRN, as expected.

The stable carrier was good for doing local tests with my Raspi+Octo-soundcard. The system is now completely configured including system time setting via the GPS module. I recorded a few days from the carrier, converted the data files into wav, reprocessed them in SpecLab: The carrier is stable and on the expected frequency, so the sample rate correction via vlfrx tools seems to work.

Forthermore i corrected some bugs in the circuit of my portable RX loop preamp for VLF (must have been late in the night when i built it up a few months ago). Now the noise is much lower. It looks promising! So it is time for a portable VLF experiment in the far field, just to check the system more seriously.

The crew of DL0AO has built up and optimised their VLF system to receive the weak 3675.005 Hz carrier in abt 220 km distance. Looks like there is something on their cardioidal spectrogram pointing to West,
http://df6nm.bplaced.net/dl0ao/VLFgrabber/vlfgrabber_dl0ao_test.htm
Something like 10 dB SNR in 31 uHz. That's not so bad!

I will run it for some more time until the trace is a bit longer. Then in some days i like to start transmitting an EbNaut message on that frequency which can be stacked until a decode appears. Markus has developed a tool for windows to do the stacking, maybe it works in that experiment... It will also be a test to see if i can decode the message from my own recording using vlfrx tools, an important step to pass...

So far so good. What are YOUR projects you are currently working on, LF/MF/VLF related?

73, Stefan

New amateur record at 970Hz

From Stefan DK7FC:

"Hi ULF friends,

Saturday night i build an active E field receiver optimised for ULF. It is using a BF862 front-end as a source follower and a LT1028 with 20 dB gain. There are 3 RC filter stages cutting off at 10 kHz. Furthermore there are two isolation transformers in series, 4:1=>1:10. In the center they are parallel resonated. This gives a further good low pass filtering and some additional gain below 3 kHz. It was a quick construction without thinking to much, soldered at night, 02 AM local time. The antenna probe is a 1m long steel rod (for welding) with 2 mm diameter. The antenna height above ground was just 2m. There were no trees in a radius of 20 m.

For transmitting i'm again using the modified 5 kV mains transformer. At 970 Hz, the antenna impedance is 342 kOhm! So i can just run 15 mA antenna current which means 3 nW ERP. The new ALC build inside SpecLab holds the 15 mA accurately and protects the transformer that way! SpecLab is a very well usable tool for transmitting on VLF/ULF, thanks to DL4YHF!!
The transmit frequency was 970.005 Hz.

I didn't expect much, thought that this distance may be to optimistic. The last signals were very weak on my tree grabber in 3.5 km distance. But that tree grabber is using loop antennas and they are not sensitive in that frequency range. So there was a certain chance to see a trace, maybe in 212 uHz???
I drove to JN49JL00EB and built up the receiver there because it is a quiet location, a nice region for a walk and, there is a good restaurant not to far!!!!!! So it was easy to spend some time there and let the Raspi (using a GPS module on the right soundcard channel, with PPS+NMEA) record for nearly 3 hours at 24 kS/s.
This is the path between TX and RX: http://no.nonsense.ee/qth/map.html?qth=JN49JL00EB&from=jn49ik00wd  A distance of 7.2 km, or 0.023 wavelengths or 14% of the distance to the far field border. So it is still a near field experiment.
It is about twice the distance i've managed in the last test.

Now i'm back in the shack, analysing the recording and to my surprise i can see a strong trace of 30 dB SNR in 424 uHz!!! See attachments in 424 uHz and 3.8 mHz.

All this makes me much more optimistic to reach farer distances. I tell you i will crack the far field border on that 309 km band! That would be a distance of 49.3 km.

There must have been some local thunderstorms not to far away, because there was QRN in the observed spectrum. So the SNR can be improved a bit by doing the next test in the late morning hours. Also the resonance of the transformers seem to be a bit to low, so maybe i can reach a bit more sensitivity when optimising that resonance. It could further help to rise the effective height of the antenna. Flat fields rather than the deep forest is the region to select now....

73, Stefan"

Amateur ULF: 5 wavelengths on the 101km band?

From Stefan DK7FC:

Hi all,

Meanwhile my 1 week taking transmission, starting  01.FEB.2017 23:30 UTC on 2970.000000 Hz at 150...170 mA is completed. I tried to leave a trace/peak into a range beyong 3 wavelengths.

Renato Romero / IK1QFK is running a 5 uHz FFT spectrogram on 2970 Hz. He's using a well working E field antenna in Cumiana/Italy.
The spectrogram is running since christmas evening 2016, available at http://www.webalice.it/rromero/live_cumiana/last-LFtest_2970.jpg

There are time markers in 1 week intervals.

I can see a dash, a trace right on the frequency. It appeared 2 days after i started transmitting, which is expected with an FFT window time of nearly 3 days. The SNR was up to 12 dB during the visual observation of incoming spectra.
Partly, the trace disappered during the transmission time (destructive interference with QRN). However i can see a resulting trace of a high average SNR and exact (!) frequency stability relative to the other traces beeing present in the spectrogram.

I would tend to call it a serious detection of my signal. Spectrogram experts, what's your opinion please?

The distance is quite exactly at 5 wavelength on that 101 km band!
It would be a first detection on ULF (0.3...3 kHz) between DL - I !

73, Stefan

Successful message decode of an amateur signal at over 3 wavelengths at ULF

Paul Nicholson has successfully decoded a message on 2.97kHz from DK7FC using clever analysis.

Hi Paul,

Am 25.01.2017 19:30, schrieb Paul Nicholson:

> f = 2970.000000 Hz
> Start time: 25.Jan.2017   07:00:00 UTC
> Symbol period: 30 s
> Characters: 5
> CRC bits: 16
> Coding 16K25A

Decoded at Bielefeld via DL4YHF (303.8km).  Copied 'DK7FC' with
Eb/N0 +4.5 dB and constant reference phase.

S/N 19.1 dB in 29.8 uHz, -60.1 dB in 2.5kHz.

Just excellent! Thanks for working out the decode!
My call passed over 3 wavelengths on ULF, that's a dream! I am sure we will manage even more.

Very interesting to see the high Eb/N0 relative to yesterday. From the calculator it should have been weaker. And the QRN didn't look much lower than yesterday, at least from here.
Some there's a relatively high uncertainty down there, and the risk of getting no decode when coming to close to the limit. The stacking is an advantage again.

I'm still working on the recordings from the weekend.  Gained a further
3dB by using very strong hum filtering, a threshold only 1.5 times the
mean amplitude and narrow notches.  Enough to suppress not just the
harmonics but also the sidebands of the harmonics.   Still no trace
here in Todmorden - yet.  Still some permutations of polarisation
and azimuth to try.

Am 23.01.2017 18:52, schrieb Paul Nicholson:

Still no trace of the signal here.  But tweaking the blanker
isn't going to go from 'no trace' to 'significant detection'.

3 dB is very significant! Congrats to that. It will also help to get better results from Renatos data. But as far as i remember he is offering the stream with the blanker already applied.
We could ask him to disable it temporarily, if that helps. If he knows what we're trying, he will do it i expect :-)

We are having fun with this!  Constantly pushing at the limits.

Oh yes, and also a lot to learn about the optimisation work for the different bands.

73, Stefan

Tests at even lower frequencies

DK7FC has been testing at even lower frequencies:

Hi ULF,

Since a few hours i'm running 15 mA antenna current on 970 Hz, the 309 km band. This requires to apply 5 kV to the antenna. You can see a very faint trace on the lower image at http://www.iup.uni-heidelberg.de/schaefer_vlf/DK7FC_VLF_Grabber2.html

Just about 10 dB SNR in 424 uHz in 3.5 km distance, or in 0.011 lambda distance. The receive antenna is a H field antenna that is not even pointing to the transmitter. Also the preamp noise is dominating the background noise on that frequency. So the RX is deaf on that band. Anyway, there is something.

The ALC into SpecLab does a very good job, it holds the antenna current stable during all the changes and working point drifts. The plot can be seen at http://www.iup.uni-heidelberg.de/schaefer_vlf/VLF/TX.png
15 mA results in an ERP of  3 nW.

My new preamp circuit is waiting for a first test together with the large loop. I hope to pick up the signal in at least 5 km distance with that preamp which is really low noise down to the lower Hz range.
An E field reeiver would be a better choise for the reception from that E field Tx antenna, at least in the lower near field. Maybe that will give another test then.

With 30 kV i could reach 0.3 uW. Not sure where this could be detected? And who knows the advantages of this part of the spectrum for our purposes!?!

Since 21:20 UTC, a 2 character EbNaut message is running. It will take 2h, 2min, 40s. Hopefully the tree grabber is available until the message ends. It will shut down in a few hours due to lack of solar energy in these days (an improvement of this system has already been prepared and waits for the installation).


73, Stefan

More ULF amateur DX

The latest ULF DX news from Stefan DK7FC:

Hi ULF,

In addition to the informations from older mails about this experiment, here are the results of the post-processing:

First, a spectrogram in 424 uHz FFT bin width (after sferic blanking) showing the whole transmission: https://dl.dropboxusercontent.com/u/19882028/ULF/65km_424uHz.jpg
The SNR reached levels up to 22 dB. Even during the (relatively) strong QRN periods at night, the transmissions are still visible. Even the EbNaut transmissions were visible. All this is about 10 dB stronger than i expected. The low winter noise levels and the quiet location certainly plays a big role here. The 'short' DFCW-10800 (3h per element) message "FC" is O copy as the experts say. Inbetween the "F" and "C" there is an EbNaut message (#2) with the content "73". One more example showing the power of EbNaut.
In the last experiments i've shown reference spactrograms beeing generated in low distance (tree grabber) just to give a better overview of what was transmitted, but this is not necessary here :-)

3 EbNaut messages were transmitted. All of them have been decoded with a strong SNR:
1st message: https://dl.dropboxusercontent.com/u/19882028/ULF/65km_EbNaut_2970Hz_Message1.png
2nd message: https://dl.dropboxusercontent.com/u/19882028/ULF/65_EbNaut_2970Hz_Message2.png
3rd message: https://dl.dropboxusercontent.com/u/19882028/ULF/65km_EbNaut_2970Hz_Message3.png

Last but not least a spectrogram showing the recorded range from 0...12 kHz, without a noise blanker: https://dl.dropboxusercontent.com/u/19882028/ULF/65km_wide.jpg

A new experiment in 140 km distance is in the pipeline. The plan is to run it in 2016.

73, Stefan

ULF amateur success

Stefan DK7FC has successfully decoded his radiated signal at 65km on 2.97kHz. He refers to an attachment that is not included here.

"Hi ULF,

My post-processing of the 4 day recording is still running, almost 50% of the data is shown on the spectrograms now.
I'm happy to confirm the successful decode of a 5 character EbNaut message over 65 km on the 101 km band, with a BIG SNR! It's the one which started on 08.DEC, 7 UTC. First there was no decode until i found that i made a mistake, the actual start of the transmission is 6:58:40 UTC, an offset of -1 symbol.
Capture in attachment. I also attach the wav file, if someone wants to play with it, the size is very small.

73, Stefan"

For EbNaut resources see: http://www.abelian.org/ebnaut/

472kHz transverter (rev K)

Several people have now built versions of my 472/500kHz transverter. The latest version is shown below which includes provision for an additional low pass filter when using a fairly long (less sharply tuned) antenna. Although some capacitors could be combined to reduce the component count, I've shown it using readily available high voltage capacitors. The 16uH inductors are 43turns of 0.71mm wire on 22mm white PVC pipe.

In the last few minutes I've been looking on 472kHz WSPR and see that SM6BHZ and DK7FC are coming through OK despite my S8 noise floor.

SM6BHZ and DK7FC this afternoon on 472kHz WSPR

PC based LF/MF receivers

There are some very neat ideas for simple LF receivers around that make use of programs like Spectran or Argo effectively as the second IF and detector stages.

DK7FC's simple 137kHz receiver

DK7FC recently posted his schematic for his 137kHz receiver which used a 4MHz crystal divided down to 125kHz using a 4060 IC with the IF at 12kHz (corresponding to 137kHz) being fed straight into the PC software. With programs like Argo the scale can be offset so that the correct frequency is displayed. Of course, there needs to be some front end filtering to remove the image, in this case at 113kHz. Using this approach one can make a very simple "stand alone" LF receiver for 137kHz weak signal reception. Such an approach is ideal for grabbers which are permanently connected to a PC anyway, uploading the received signals to the internet.

VLF amateur activity

There is a new VLF grabber at Darmstadt Germany that may be useful for 8.97kHz tests. It is at http://skmail.ikp.physik.tu-darmstadt.de/gvw/grabber.html. The grabber is primarliy there for VLF research into earthquake precursors.

Stefan DK7FC reports that the permit he has to use a 300m kite antenna expires soon, so he may try a further soon before that date.  Chris G3XIZ is still hoping to resume VLF tests once a new loading coil is wound. He is looking for a suitable (very long!) source of PVC covered wire.

Germany- Venezuela on 136kHz

DK7FC has been helping YV7MAE set up a grabber for 136kHz and over the last month they have been improving the system day by day. Last night Stefan's DFCW signal was copied quite well for the first time over a distance of 7818km. This is the first time a European station has been copied in South America I believe on this band. The grabber can be seen at http://dl.dropbox.com/u/74746618/LF/YV7MAE_LF_Grabber.html .

VLF activity this last week

Whilst I was away on holiday there was considerable activity around 8.970kHz from Europe with Henny PA3CPM now putting a consistant signal from his small home station antenna on the G3ZJO grabber. Activity is continuing this weekend.

One of my priorities in the next 2 weeks is to get my VLF receive set-up back in full working order as this has been off-air for a couple of months. I will try a new E-field probe this time around and see how results compare with my 80m square wire loop. The PA0RDT or DK7FC E-field probes are well proven designs that work well if mounted high and in a low noise environment. See https://sites.google.com/site/sub9khz/antennas for details. Antenna size is less important than S/N and dynamic range on VLF RX. This is why tiny voltage probe antennas can work so well.

QRM on VLF?

DK7FC, PA3CPM and DF6NM have all been TXing today around 8.970kHz with reception reports coming in from many of the western European grabbers. DF6NM is running some 20dB less ERP than Stefan yet is appearing on UK grabbers quite well just HF of DK7FC. PA3CPM is a much weaker signal although he has been copied by Paul Nicholson in Todmorden UK. Activity is likely to continue over the weekend. Here is a screen grab from Eddie G3ZJO's VLF grabber today showing 2 of the active stations quite clearly. Notice the timescale on Eddie's grabber: between markers it is 4 hours in his DFCW6000 window, so don't expect snappy QSOs on VLF.

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.

Busy amateur VLF weekend

G3ZJO's reception of DK7FC on 8.97kHz

Yesterday's test by DK7FC from his fixed location was a resounding success with reception all over Europe by many stations including G3ZJO, G3WCD and G3KEV, and what is believed to be the first transatlantic reception of an amateur VLF signal by a station in the Eastern USA. Results are being checked as I write.

Stefan's ERP was later re-calculated as around 800uW. It is incredible that such a tiny VLF signal can be detected so far away. If confirmed, this certainly heralds the dawn of a new and exciting phase of VLF amateur work. With another 3-6dB ERP, worldwide amateur VLF DX is now a real possibility. Of course such VLF DX reception requires incredible frequency stability, very narrow RX filters and long signal integration times; signals are far too weak to hear.

Also, Marcus DF6NM ran a 8.97kHz test today using a kite antenna. G3ZJO received a good signal in IO92ng 20dB above the noise in 424uHz bandwidth. Marcus was also well received by many other stations across Europe.

In summary, this weekend has been a BUSY one on the Dreamer's Band.

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.