New amateur ULF distance record

Paul Nicholson posted this on a Facebook group earlier:

"After much computing effort by Jacek Lipkowski SQ5BPF, Stefan's 2970.1 Hz message sent on 6th April was successfully decoded from well beneath the noise in Warsaw, 975km away - a new amateur radio distance record at ULF. Eb/N0 was -0.4dB."

Stefan DK7FC is in Germany and is a great VLF/ULF experimenter.

Amateur VLF

VLF seems to have been busy in the amateur fraternity of late. There have been tests around 8.27, 5.17 and even 2.97kHz.

Casual listening will not bring results: long stable transmissions are needed together with very stable, narrowband reception if amateur VLF/ULF signals are to be detected. Commercial VLF signals on the other hand are very strong as most use high power and big antennas.

The photo shows DF6NM's loading coil for 5.17kHz today.

See https://sites.google.com/site/sub9khz/ .

Amateur radio below 9kHz

Until a few years ago, the conventional wisdom was that you needed huge power and huge antennas to be copied "beyond the garden fence" at VLF and ULF. In recent years much has changed and time and again great distances have been covered by amateurs with quite low power and modest antennas.

The trick is great stability, very narrow bandwidths and long integration times, often of days. For several years just detecting a carrier was enough, but in recent times people have been sending simple messages using EbNaut software.

When at the old QTH I detected signals from several European countries using simple, homemade gear and free software.

Although not totally up to date at all times, I try to update news of amateur VLF and ULF experiments at https://sites.google.com/site/sub9khz/ .

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/

More ULF tests in Germany

Stefan DK7FC has been busy winding a loading coil so he can carry out radiated tests at 2.97kHz at a distance of 65km. He has already tested successfully at 30km. Up to now his loading coil has not quite reached resonance. At these frequencies very slow data rates are needed, but he is hopeful of success.

More success on the ULF 101km (2.97kHz) band

Today I heard that Stefan DK7FC's 100nW ERP signal on 2.97kHz VLF was received in a 212uHz bandwidth at 16.8km. He will soon be trying to receive this radiated signal at 30km. I wish him every success.

Hi ULF friends,
This is the summary of my portable RX experiment in 16.8 km distance to my transmit site. It is into the far field of the 101 km RF wave.
A 100 nW ERP signal was sent and recorded for nearly 2 days.
The recording was started on Saturday, 30th of July (14:58 UTC) and was finished on Monday, 01st of August (12:25 UTC). The transmission was a carrier sent on 2970.000 Hz, it was shifted by +2.5 mHz at 8 UTC on Sunday and again shifted by -5 mHz on Monday, 8 UTC.
In the post processing of nearly 30 GB wav files the signal was successfully detected.
Due to the exceptionally high QRN levels (even for the summer time), the SNR was lower than expected, however the traces and frequency shifts are clearly visible.
Spectrogram of the signal in 212 uHz FFT bin width: https://dl.dropboxusercontent.com/u/19882028/ULF/17km212.jpg
Spectrogram of the signal in 47 uHz FFT bin width: https://dl.dropboxusercontent.com/u/19882028/ULF/17km47.jpg
A wideband spectrogram giving an idea about the natural and man made noise conditions as well as the frequency response of the tuned loop antenna: https://dl.dropboxusercontent.com/u/19882028/ULF/17kmwide.jpg
Wideband spectrogram zoomed to the spectrum of interest: https://dl.dropboxusercontent.com/u/19882028/ULF/17kmwide3.jpg
The best SNR shown is 12 dB in 212 uHz and 17 dB in 47 uHz.
During the post-processing procedure it happened that SpecLab has plotted a few pixel twice. I don't know the reason.
It looks like i am now seeing the natural background noise on 2970 Hz even in quiet periods (the faint vertical traces). However the man made noise is still playing a role in this QTH.
Further informations can be found in the older emails below.
73, Stefan
PS: A next experiment is planned in a few weeks. The goal is 30 km distance. With lower QRN levels, a better tuned antenna and higher power (already running!) this should give even better results.

ULF Amateur Experiments

Stefan DK7FC is always experimenting at VLF and ULF. Recently he has been radiating a signal at 2.97kHz and he has detected his own signal at 9km. This is not earth mode. He is trying to get reports from much further.

See https://sites.google.com/site/sub9khz/ .