VLF Amateur News 2018

December 1st 2018

It is all happening too fast! Stefan DK7FC has been experimenting at SLF frequencies going even lower in frequency. Of course at these frequencies the far field is very far away.

Hi SLF,

Yesterday, a 45 character EbNaut was transmitted at 80.005 Hz. It was received on my tree in 3.5 km distance. After the improvement of the RX antenna it looks like i gained about 2.5 dB SNR. It was an easy decode, the message could have been transmitted 4 times faster.

Capture attached :-)

73, Stefan

PS: With that SNR, a 5 character message could be transferred out to 7 km distance in less than 1 day.

Nov 18th 2018

A reminder, especially to newcomers that casual listening for amateur VLF signals is most unlikely to succeed. Most amateur transmissions require extremely long transmissions, stable very narrow bandwidths and specialised software. This is a pity, but the reality. By contrast, commercial signals can be easily copied by ear, although many are MSK, so will be meaningless be ear.

I am unaware of any recent amateur experiments.

The heritage station SAQ (on 17.2kHz) does send special messages in CW. They have a lot of power and very big antennas! Sometimes SAQ sends QSL cards (see left).

SAQ (17.2kHz) QSL card

Nov 11th 2018

As usual Stefan DK7FC has been at the frontiers again! This time, he is experimenting at SLF.

October 6th 2018

Riccardo IW4DXW has been doing some VLF tests lately although most stations in Europe have failed to decode him. He hopes to do some "guard rail" loop tests shortly, inspired by Stefan.

September 10th 2018

Excellent copy in the UK by Paul Nicholson of VO1NA's 10uW ERP on 8.27kHz

VO1NA from Newfoundland with 10uW must hold the record for

the longest running VLF transmission!

Coming in well the last couple of days -

http://78.46.38.217/fbins3.html#p=1536487200&b=280&s=sp&m=cardioid&w=r&h=62&z1=0.34&z2=0.64&c=1

An ERP improvement, or good propagation?

--

Paul Nicholson

August 7th 2018

More news from Germany (DK7FC):

Hi ULF,

Despite the ultra high temperatures (> 35 °C here) i worked 6 hours to separate the wires from the loudspeaker cable and rolled it out between the two guide rails. About 850 m of wire was needed to connect them. I define the antenna length as from the center of the guide rails, so 900m is quite accurate.

After that work i was quite down but i couldn't wait another day for the first results of the measurements. So i characterised the transmit frequency response (V/I ratio and reactive component) from DC to 8.27 kHz on frequencies of interest. I used a good oscilloscope to measure the voltage / current waveforms and the phase between them. Then i added a series capacity to resonate the earth loop. You can find details in the attached table. The inductivity is calculated from the frequency and the tuning capacity.

To my satisfaction the DC resistance showed exactly as expected: 79.4 Ohm. So i reduced the losses by more than 50 %, relative to the 0.4 mm diameter Cu wire i used the weekend before :-)

Attached i also show a plot from the scope showing the un-tuned (no C in series) loop at 8.27 kHz. The yellow trace is the voltage at 20 V/div (100:1 divider).. The antenna current is blue and at 250 mA/div (measured across a 0.2 Ohm shunt resistor). Also attached, the tuned antenna at 8.27 kHz showing a good sine curve for the current showing 750 mA (rms).

The next day i transmitted into the ULF band. Results will come soon in a separate email.

73, Stefan

August 6th 2018

Stefan has been carrying on his experiments using an earth-electrode "antenna" at lower and lower frequencies and setting some new records

Hi ULF,

On Sunday, 5th 2018 i successfully crossed the far field border on 2470 Hz for the first time. That's the 121 km band. Later i even crossed it on 1970 Hz, the 152 km band. These are two new records of the lowest frequency signals generated by amateurs and received in the far field. The distance between RX and TX was 55.6 km . The far field for 2470 Hz starts at 19.4 km distance. For 1970 Hz it starts at 24.3 km distance. The RX antenna and the TX antennas were loops!

By running about 100 W (PA DC input) i managed to get 910 mA antenna current on 2470 Hz into the earth loop in JN39WI. Here i transmitted a plain carrier from 06:13...07:15 UTC.

Later i QSYed to 1970 Hz and here i got 910 mA as well. The 1970 Hz transmission took place from 07:19...08:21 UTC.

Despite beeing in the middle of a large forest there was good internet connectivity and so i was able so watch my own grabber window showing the band activity on 2470 Hz in a spectrogram of 424 uHz FFT bin width, which is very wide for that frequency range! The spectrogram uses a Hann window and the FFT window time is about 40 minutes, so it took some time until a peak builts up. But already after 20 minutes i saw that something happens! After 40 minutes the carrier transmission reached an SNR of about 20 dB! It was a relatively quiet morning for early August.

All the VLF stream data is stored into a ~ 12 day covering buffer so i have the chance to optimise the filter settings and antenna mixing in a postprocessing to achieve the best SNR from the system.

For the 1970 Hz transmission there was no spectrogram available but since i had internet access and a Linux notebook available, i processed the VLF stream data (via SSH remote access to the storage PC) during the transmission and followed the peak's SNR building up!

It clearly looks like this antenna outperforms my large inverted L in 30 m above the ground, at least into the ULF range! This opens up a new room for experimentation on the way down to DC! :-) Now i need to get rid of these output transformers since they will become problematic for wide-band experimentation on ULF / SLF.

Now, attached you can find two images showing spectrum peaks from the two bands, out of the 55.6 km distance. The complete transmission time is here integrated in one peak. Since the carrier S/N can also be calculated from decoding a '*' message in EbNaut, i also show the results for such calculation along with the whole postprocessing chain.

Spectrograms will be produced as well, but this will take a few hours here...

73, Stefan

July 28th 2018

More VLF tests from Germany. Stefan is seeing if he can be detected by Paul in Todmorden, UK, using 75W TX and an earth-electrode antenna on 8.27kHz. I am happy to announce that Stefan was easily copied on 8.27kHz in the UK.

Hi VLF,

I'm sitting in my car while writing this email. I'm in JN39WI96GX and i transmit on 8270.000 Hz with a GPS locked signal generator into an about 450 m long earth antenna using two guide rails as the earth electrodes on both ends. On each end there are 16 (18) massive T-T poles holding the guide rail, providing a super good earth coupling. I measured that they are connected to each other.

The transmitter is on the air since 9:08 UTC running 550 mA with just 75 W DC inout power into my hand warm lossy linear mode VLF PA!

I'm amazed about the low losses! At DC i got 447 mA at 50.9 V. The wire is 0.4 mm diameter so it has 63 Ohm. That means the ground loss is just 50 Ohm !!!! Amazing! And i have no efforts to build up a ground connection here, i just need to connect the wire. Since the wire losses are higher than the ground losses, i can get maybe 2 dB more signal when buying some better wire. I already found a source that offers 0.75 mm^2 100 m loudspeaker cable (i.e. 200m wire)for just 13 EUR....

BTW i even have an ugly old scope here which is battery powered. I can see that the phase of voltage and current is slightly inductive, maybe 30 deg or so. So i could series resonate the antenna with some C. This is for the next experiment...

The signal becomes visible on my grabber now, in 424 uHz and also some bright pixels in the 3.8 mHz window.

I'm going to stop the carrier at 10:08 UTC, after 1 hour. Then i'll continue on 5.17 kHz!

BTW the antenna , if it works like a real loop, is beaming directly to Paul Nicholson ;-)

73, Stefan

July 14th 2018

Since 4:43 UT I'm sending a 10 uW carrier on 8270.0025 Hz, trying to leave a coloured trace on the new DL0AO 424 uHz RDF-spectrogram:

https://vlf.u01.de (scroll down to the middle of the page), or https://vlf.u01.de/VLFgrabber/vlf12.jpg

Best wishes,

Markus (DF6NM)

July 1st 2018

A better remote RX set up.

Hi VLF,

In the last weeks i finally installed the octo-soundcard for the raspberry pi on the tree. Now i can listen on 6 channels simultaneously. So now i am able to track the signals of both of my orthogonal VLF loops mounted in 18m above the ground.

The raspi is running vlfrx-tools. A GPS module provides accurate timing for the system, so it does not depend of an available internet connection providing the ntp service. The sample rate is corrected on the tree and a stream is generated which includes timestamps.

2 channels are used for the MF loops. Another 2 channels is used for the VLF loops now and one channel is for the 1PPS+NMEA. So there is 1 channel left! The idea is to build an E-field RX for VLF so i can generate a 360° RDF spectrogram. But it would also be nice to have something for LF... There should be even more channels on the input :-)

Anyway, now i can already generate RDF spectrograms. They are hidden on my grabber page, http://www.iup.uni-heidelberg.de/schaefer_vlf/DK7FC_VLF_Grabber2.html

If you click on one of the spectrograms, it will switch to the RDF mode. Not all of the images are available in RDF mode. The other channel show the signals of the E-W loop. I should add a 3rd image showing the N-S loop but i have to see where i can find another computer running a few more SL instances :-)

So far i'm still fighting with stream interruptions. Streaming 5 channels (two of them are vorbis streams and three of them are flac streams (lossless compression!)) means a significant data rate over the 2.4 GHz WLAN link. Thus, another task for the coming days is to move to 5 GHz where higher data rates should be no problem.

I'm saving 100 GB of the data of the VLF loop so i can post-process the signals of about the last 2 weeks (the stream is resampled to 24 kS/s). That means i can configure a 'totary loop', software based.

So now, if VO1NA and IW4DXW transmits a message in the same time, i can watch for both of their signals and even 'turn' the loop for the best S/N for each station :-)

Joe's carrier has been very weak here and the common dark time is very low and but the QRN is very high. So there are doubts that i will detect the carrier but it may be worth a try :-)

If someone else wants to try to transmit down there, don't hestitate :-)

73, Stefan

June 6th 2018

More ULF tests a few days ago

Hello dear friends of the Ultra Low Frequencies,

I want to report about a short experiment i've done on thursday morning.

Early in the morning i placed my RX loop antenna (0.8m diameter, 84 turns, preamp) and an active E field antenna (now using a J310) in JN49KK03HQ . That's a distance of 11.8 km to the TX antenna, about 3x farer than the best distance crossed on that frequency so far, but still well into the near field.

For about two hours i transmitted a carrier on 1570.01 Hz followed by an EbNaut message (3 chars, 16K21A, CRC20, 6 sec/symbol). The ERP was just 90 nW.

This time the E field antenna was not sourrounded by trees. Although it was mounted just 2...3 m above the ground, reception in the E field was excellent. A spectrum peak integrating two hours of carrier transmission reaches > 30 dB SNR in 134 uHz, see attachment.

Unfortunately there was a bad contact on the BNC connector of the H field (problems of portable equipment which is built up and down several times | headless recorder, i.e. no chance to check if all works well) , but at least during a part of the EbNaut message it was working, so a comparison of the E and H performance is possible: The E-field SNR is about 15 dB higher than the H-field SNR. This is expected when using an E-field antenna in the near field to receive a signal radiated from an E-field antenna.

But it is not only propagation, it is also the lower hum components in the E field.

Another attachment shows the extraction, filtering and sferic blanking out of the recorded signal as well as the 3 character message decode, E field only.

This experiment was done just for fun, to check the equipment and to spend some hours in the nature :-)

Another one will be done very soon (today?), but then in the far field!

73, Stefan

May 26th 2018

Stefan has been testing on the 191km band for about 30 days. So far his best DX is 3.5km.

Hello ULF friends,

I just opened up a new band by starting some activity on 1570 Hz ! It is the 191 km band! :-)

Since 8 UTC a carrier is running at 1570.01 Hz. Soon the first trace will appear on a spectrogram from my tree which is in 3.5 km distance from the transmitter.

See the developing trace at http://www.iup.uni-heidelberg.de/schaefer_vlf/DK7FC_VLF_Grabber2.html

The spectrogram scrolls with 10 minutes/pixel.

The carrier will stay on the air for 2.5 hours. It is just a first test. So far the antenna current is just 27 mA but tonite i'll try to reach the target level of 58 mA which means 12 kV again acros the special iron cored coil. This will mean about 120 nW ERP then.

DL0AO is already watching the band. I hope to be received by Paul and at the reomte site of DL4YHF. I'm not planning to do /p RX experiments on that band, just focusing on these 3 RX stations.

73, Stefan

May 13th 2018

Riccardo's EbNaut transmissions from Italy on VLF (8270.003Hz) have been decoded in Germany.

May 9th 2018

Yet more tests from Italy by Riccardo IW4DXW.

Hi Stefan, Lubos, Paul, VLF

Ok Stefan :-), here we go!

I'm starting a series of EbNaut transmissions, from 0800 UTC (9 May) every 8 hours. Then 3 messages per day (0000, 0800, 1600 UTC).

QRG: 8270.003

2 ch.

30 sec./sym.

coding 16K21A

CRC 28

duration: 8h 00'

antenna current: 600 mA

many thanks for reports!

May 7th 2018

Riccardo continues his VLF tests from Italy:

Lubos,

many thanks for your report!

I'm testing the coil for long transmissions; I have observed, for my first time, that atmospheric conditions affects antenna current: for example, today it's been a sunny and dry morning, in fact I reach 625mA; in the afternoon the sky was so cloudy and I have measured only 570mA. Now the value is stabilized around 590mA (relative humidity's still high: 86%).

I'm preparing an EbNaut setup for next days: I will announce details soon.

April 28th 2018

Riccardo's VLF signal has been copied across Europe! As an example:

A very nice signal this morning,

http://78.46.38.217/fbins3.html#p=1524736800&b=130&s=sp&m=cardioid&w=r&h=62&z1=0.34&z2=0.64&c=1&mb=643,121,724,224,1

Bearing 126.9, great circle is 127.8.

--

Paul Nicholson

By the way, Paul is in the UK, but these VLF signals have also been copied in Germany and the Czech Republic, possibly elsewhere too.

April 27th 2018

More VLF from Italy. VLF: carrier at 8270.003.

Hi VLF,

A new carrier test is running with about 610mA.

Now, with last SL version, the PLL configuration made by Markus seems to works well here, the phase is stable. I started this test yesterday at about 10:00 UTC.

I'm looking for an adequate conditional statement that permits to inhibit the audio (and the TX) in case of an excess of antenna current drop. Any suggestion?

All the best

73 de Riccardo IW4DXW

March 13th 2018

Lubos, OK2BVG, JN88KS has his grabber on and is seeing a station on 8.2702kHz.

March 3rd 2018

Following recent successes with EbNaut test across the Atlantic on 8.27kHz with W1VD (Jay), Stefan is now trying a 5 character message and expects to be successfully decoded with stacking after several days.

Feb 20th 2018

Stefan's transmission:

f = 8270.1000 Hz

Start time: 12.FEB.2018 22:32:00 UTC (daily)

Symbol period: 32 s

Characters: 1

CRC bits: 24

Coding 16K21A

Duration: 07:06:40 [hh:mm:ss]

Antenna current: 700 mA

After a week of trying ... including two nights with TX problems, one night with RX problems and one night with high noise levels ... a successful decode of Stefan's message was made on last night's transmission. s/n in 39 uHz 10.5 dB and Eb/N0 2.54 dB. It was pretty convincing as the decode popped up in the 0,0,0,0 phase trial and only improved thereafter.

Congrats Stefan on what appears to be the first E>W T/A on Dreamers Band!

Jay W1VD

Feb 18th 2018

It looks like the first amateur VLF transmission for the USA to Europe has occurred? This was 6 days ago.

VLF,

OK, Jay responded to me personally. We will take the challenge.

The first transmission is already running:

f = 8270.1000 Hz

Start time: 12.FEB.2018 22:32:00 UTC (daily)

Symbol period: 32 s

Characters: 1

CRC bits: 24

Coding 16K21A

Duration: 07:06:40 [hh:mm:ss]

Antenna current: 700 mA

Reports welcome :-)

73, Stefan

Feb 11th 2018

Many VLF projects require good GPS timing. Paul Nicholson reports good service from CSG shop in Latvia. I have heard some good reports of it, although I have not (yet) used it myself. They do some good GPS kit as well as 2.4 and 5.8GHz ATV modules.

See http://www.csgshop.com/

Feb 9th 2018

More USA VLF action:

Ward K7PO wrote:

> I'm transmitting on 8270.0 now, showing 600 ma antenna

> current. Ideally, it runs for the next 24 hours (if I have

> enough air on the amp!)

Getting a strong signal at 8270 Hz at Hawley Texas, distance

approx 1200 km from Tonopah.

http://abelian.org/vlf/tmp/180209a.gif

This is almost certainly your signal but there is a large

frequency spread. Is the GPS lock working correctly?

If the signal was concentrated on one frequency, I think it

would be visible at much greater distance.

S/N of the sharp peak at 8270.000000 is about 16.5 dB in

34.7 uHz.

...

The same signal appears at Forest Virginia, 3070km, with

S/N 12.0 dB.

http://abelian.org/vlf/tmp/180209b.gif

There we see not so much spread of the signal energy, so

perhaps the rx timing at Hawley was upset.

If your signal makes it to the East Coast, it is likely to

cross the Atlantic. Now I look for the signal at Todmorden.

Hopefully the carrier continues!

--

Paul Nicholson

Feb 8th 2018

More ULF experiments by Stefan:

Hello dear friends of the Ultra Low Frequencies,

Update:

There are a few things to note so far:

I made a mistake in the calculation of the ERP. It is not 10 nW but rather 18 nW.

All transmissions seemed to go out as intended. The stream from the local tree was interrupted almost daily due to lack of solar energy but at least a few hours came through. From these few hours i got decodes of each carrier transmissions. I also got decodes of all EbNaut messages. So things went well from the TX site it seems.

The 36 mA antenna current (12 kV antenna voltage) was running for 8 days without a single interruption. The constructed resonating transformer has done its job flawlessly.

Since i decided to take back the RX equipment on the 7th of February, there was some more time for another EbNaut message:

06.Feb, 17:30 UTC: EbNaut, 16K21A, 1 char, 90 sec, CRC27 (21:12:00)

The experiment stopped at 15:45 UTC. BTW the exact location was JN49BK33UG That is a distance of 40.5 km to the TX site. But so far there are no decodes or traces, so no success so far.

The next good step is that the whole RX equipment has still been in its place, nothing stolen, nothing damaged. The Raspi was still running after 8 days. The Raspi was supplied by two 12 V / 26 Ah lead gel accus. They were standing in the snow and discharged to 11.8 V! The two accus for the preamps of the loop and vertical were still above 12.3 V. So that was all fine too!

Now the stuff is sorted, cleaned and the accus are charging and warming up again here.

I just started the Raspi and checked the data on the 64 GB USB stick. This looks good and promising, see attachment. And it looks like there were no timing breaks of the GPS module.

For the first time i run the recording using vlfrx tooly by Paul and the octo soundcard. Also it is the first set of data i have available to build a cardioid antenna by software... Exciting stuff.

The recording process by vlfrx tools saves to a new file each day.

Here the files are 7.8 GB large: 2 channels * 24000 samples/(channel*second) * 16 bit/sample * 3600 seconds/hour * 24 hours/day * 1/8 Byte/bit * 1/1024 kByte/Byte * 1/1024 MBity/kByte * 1/1024 GByte/MByte = 7.72 GB/day

Obviously the recording process was stopped during the last night 03:58 UTC because the USB stick capacity seems to be just 58 GB actually. The recording is started/stopped by switching a switch which is connected to one of the GPIO pins. This is necessary because in the field there is no monitor and no keyboard of course. At start-up, a scripts is executed which checks the logic level of the pin where the switch is connected... During the recording process, a loop is running within this script which periodically checks the remaining available

space of the data carrier. As soon as the remaining space becomes less than 100 kB, the recording process is stopped. This ensures that there is still enough space to save the log files which are written at the end of the recording process. It also ensures that there are no crashes and unwanted data loss, broken files etc...

In a few days i can report about the results, so stay tuned...

73, Stefan

Feb 4th 2018

News of DK1IS's VLF station:

Hello group,

having been QRV on LF since 1999 and on MF since 2013 now I try to dream on VLF too. First test results on 8270 Hz were quite encouraging - thanks to all reporting stations and to Paul Nicholson for the compilation! On 2018-01-28 13:00,+6h, Paul analysed my signal in 46.3 uHz:

Bielefeld (DL4YHF 384.3 km): 15.7 dB, -27.6 dB/1Hz http://abelian.org/vlf/tmp/180128a.gif

Cumiana (IK1QFK 601.4 km): 13.0 dB, -30.3 dB/1Hz http://abelian.org/vlf/tmp/180128b.gif

Warsaw (SQ5BPF 710.2 km): 10.5 dB, -32.8 dB/1Hz http://abelian.org/vlf/tmp/180128c.gif

Todmorden (Paul Nicholson 1071.3 km, ODX): 15.6 dB, -27.7 dB/1Hz http://abelian.org/vlf/tmp/180128d.gif

Up to now I´m just testing the system with plain carriers from a synthesizer but later on there will be more sophisticated modes in use generated by a GPS controlled PC. Here is some information about my new VLF station and first experiences with its components - hoping it won´t bother too much:

TX exciter: Frequency synthesizer Schomandl ND 60 M resp. MG 100 M, resolution 0.1 Hz. Although being controlled by an external rubidium standard, at audio frequencies precision and stability of both of these units are only in the 10 exp -8 range for some unknown reasons. At LF, MF and HF they perform much better - so I don´t care for the future.

TX power amplifier: Commercial (low cost) stereo PA Omnitronic E-900 Mk 2, according to datasheet 2 x 300 W stereo output at 8 Ohms resp. 900 W in mono bridged mode. In spite of the distortions staying low one can´t use these maximum powers with long key-down periods due to thermal overload. I already realized minor improvements by modifying the internal air flow. Bridged mode doesn´t work because of phase differences between the channels at least at 8,27 kHz (Markus, DF6NM, has reported on similar experiences with another PA). So I only use one of the stereo channels, the available power being sufficient anyway.

TX antenna: The idea was to use the exsisting facilities as far as possible and to be able to reactivate all former modes (LF, MF, HF) in a simple way. So I stayed with my proven Marconi-T-antenna, 13 m up with a top load of 4 wires, 33 m long and seperated 1 m. At 8,27 kHz its mesured loss resistance is about 160 Ohms and its total capacity to ground about 660 pF, the latter in good accordance to Watt´s formulae. The loading coil is somewhat different of the usual concepts because I wanted a very versatile unit with low required space to fit into the antenna box at the back of my arbour. I came out with a construction of 60 ready bought ferrite inductors 10 mH / 600 mA rms (Murata) mounted on 4 ring-shaped layers of ply wood, 30 cm diameter and 30 cm height over all. The variation range by tapping and the use of variable mutual coupling is 10 ... 700 mH . In a work bench resonance test the 700 mH coil easily withstood 20 kV rms without any partial discharge or overheating. Fine tuning is accomplished by an additional variometer 7 ... 14 mH made by two pairs of the same ferrite inductors, mechanically twistable against each other face to face. A rms current meter (1 A full scale) allows to tune the coil assmbly to resonance. When increasing the current the resultant inductance of the coil also increases a little bit - usually one would expect a decrease. I think this is because the mutual coupling between the coil layers increases with higher drive due to the stronger stray fields. The bandwidth of the whole system being about 180 Hz at -3 dB, this increase isn´t really cumbersome. Up to now it seems to be unnecessary to re-tune the antenna by reason of windsway. Should this become essential after all, I already have built an alternative variometer using a large ferrite pot core. With an additional orthogonal DC winding through the cente hole it acts as a steerable inductor like a transductor - it works fine.

Matching transformers: Although matching 8 Ohms to 300 ... 450 Ohms (sum of all loss resistances - forget the tiny radiation resistance) at AF could be done in a single step I use two transformers to avoid high currents on the 25 m long RG 213 cable from the shack to the arbour. Both transformers are former mains transformers size EI 120 b with laminated iron cores and modified windings, the first from 8 to 50 Ohms, the second from 50 to (tapped) 300 ...450 Ohms. The latters secondary winding is feeding the antenna between ground and the variometer / loading coil assembly. The sound emission can be greatly reduced by soaking the laminated core with low viskosity oil which after some time fills all of the capillaries. By the way, it´s wise to insert two electrolytic capacitors with high AC current capability back to back into the line from the PA to the matching transformer (I use 2 x 22000 uF / 25V). The DC component from the PA output is usually in the range of some tens of millivolts only but the DC resistance of the transformer primary winding is very low too.

Power distribution: At resonance with L = 560 mH and 600 mA the reactive power of the loading coil assembly is about 10.5 kva. Assuming Q = 46 from the bandwidth, the active power is about 230 W. This fits well with the PA loading. Corresponding to the computer model being used the ERP is somewhere between 30 ... 70 microwatts at 600 mA.

RX: According to the very weak signals and the special modes on VLF, one has to use highly sophisticated audio software like SpectrumLab for reception. It´s always a little bit frustrating that I can´t hear my own signal even at the VLF RX site at our club station DL0AO only 6 km away in a forest. The signal is only visible on special grabbers accessible via www like that from DL0AO: http://www.df6nm.bplaced.net/dl0ao/VLFgrabber/vlfgrabber_dl0ao_test.htm or at your own SpectrumLab if you have installed it and if you have a suitable VLF RX antenna.

Finally I want to thank Marcus (DF6NM) and Stefan (DK7FC) for all their invaluable advice and Wolf (DL4YHF) for his most ingenious SpectrumLab software - it´s essential for VLF work!

Hope to see you on VLF.

73,

Tom, DK1IS

www.qrz.com/db/dk1is

Jan 31st 2018

Even more tests on 970Hz ULF

Hi all,

Since yesterday, ~ 17 UTC, i'm running a new portable experiment on 970 Hz, or the 309 km band. The receiver site is somewhere in the forest in JN49BK, a distance of 40 km to the TX site.

I carried a lot of accus to that location and the USB stick where the data is written on has 64 GB, so i can run the experiment for more than one week! :-)

For the first time i'm using two antennas. An active E field antenna with a 1.5 m long steel wire as the capacitive probe. It is mounted on a 10 m high pole. The E field preamp is supplied by a separate battery and uses an isolation transformer with a low pass filter applied.

The second antenna is my compact loop with 80 cm diameter and 84 turns. It uses a low noise preamp (also supplied by a separate battery) using a LT1028. This loop RX worked surprisingly well on 4470 Hz when beeing in France last September. Hopefully it will pick up the signal.

Unfortunately the E field antenna is not very high above the sourrounding trees, so the sensitivity may be limited. Also the H field antenna showed much more mains hum than expected in this location. So it may be a bit questionable if the experiment will be successful. The long transmissions will allow to stack carrier transmissions and/or EbNaut transmissions though...

Running 36 mA antenna current means an ERP of 10 nW on that frequency.

My transmission plan is:

30.JAN, 17 UTC: Carrier on 970.005 Hz

01.Feb, 17 UTC: Carrier on 970.0025 Hz

02.Feb, 17 UTC: EbNaut, 16K21A, 2 char, 100 sec, CRC22 (24 hours)

03.Feb, 17 UTC: EbNaut, 16K21A, 2 char, 100 sec, CRC22 (24 hours)

04.Feb, 17 UTC: EbNaut, 16K21A, 5 char, 80 sec, CRC17 (23:49:20)

05.Feb, 17 UTC: EbNaut, 16K21A, 5 char, 80 sec, CRC17 (23:49:20)

Not sure if someone else can pick up the signal. Most likely not. But new components to rise the voltage to 20 kV in a next experiment are already in preparation...

73, Stefan

Jan 29th 2018

VLF is getting busy!

Coming through well here. A nice start!

> The signal is well visible in Todmorden,

Later I'll check the online natural radio receivers.

What is the latitude/longitude of the transmitter?

In Omni mode we have DK1IS, IW4DXW, and VO1NA

http://78.46.38.217/fbins3.html#p=1517155200&b=115&s=sp&m=omni&w=h&h=62&z1=0.29&z2=0.59&c=1

--

Paul Nicholson

--

Jan 28th 2018

New VLF amateur station

Great news: Tom DK1IS is running a new VLF transmit station, located in the city of Amberg, about 6 km east of the DL0AO grabber. His carrier on 8270.0002 Hz is very bright there

http://df6nm.bplaced.net/dl0ao/VLFgrabber/vlfgrabber_dl0ao_test.htm

The signal is well visible in Todmorden, along with Riccardo IW4DXW:

http://78.46.38.217/fbins3.html#p=1517151600&b=110&s=sp&m=cardioid&w=h&h=62&z1=0.29&z2=0.62&c=5

There are also good traces in Heidelberg and Nuernberg.

Tom, welcome to Dreamer's band!

73 and good DX,

Markus (DF6NM)

Jan 25th 2018

Stefan DK7FC is about to experiment at 970Hz ULF

Hello dear friends of the Ultra Low Frequencies :-)

Since 21:05 UTC i'm running a carrier on 970.005 Hz.

With a lot of work i built a new ULF coil for 970 Hz. It's Q is just 11! For the next experiment, the target voltage is 12 kV, that means 36 mA antenna current and about 10 nW ERP!!

Since the Q of the coil is so low i decided to add a primary winding in this experiment, so actually it is a transformer now.

Here is an image showing the transformer inside the large waterproof PVC tube on the roof: http://www.iup.uni-heidelberg.de/schaefer_vlf/ULF/ULF_coil_970Hz.jpg

The core material is that special stuff i bought a few months ago, see the old mail below. The iron cross section area is 40 mm x 40 mm. With acceptable upheating i can apply up to 4 V / turn, which means 0.4 T at 970 Hz. Not much but better than ferrite and it has quite a high mu r! Also i can form all wanted geometries, which is a bit hard when using ferrite :-)

On the core there are 4 windings which have 1000 (hand-wound!) turns each. So i could apply up to 16 kV. But in the coming experiment i stay at 3 V / turn.

The core is floating, so its potential against ground is given by the RC network of the geometry of the arrangement. I spent loads of Kapton tape which is just excellent for all such applications!

Oh, the iron core has two air gaps of course. It should be about 2x 0.15 mm. The Kapton tape realising the air gap also helps to isolate the two half cores from each other. This helps to reduce the E field stress.

I just made a frequency sweep and found that the actual resonance is near 1100 Hz. But the Q is low and the TX power is low too. The only disadvantage beeing outside the resonance should be a higher primary voltage and higher PA losses.

SpecLab and the antenna current regulator carefully holds the phase and target current! This is important here. A view into the box showing the PA, power supply, PA output transformer (yes, i'm still using N30 ferrite at 970 Hz!! But just 1 V / turn on a AL=10800 nH core), digital and analog antenna current measurement: http://www.iup.uni-heidelberg.de/schaefer_vlf/ULF/20mA@970Hz.jpg

I intend to run the carrier for a hour and then check the temperatures. Later i want o rise to 24 mA and check again....

More soon...

73, Stefan

Am 16.11.2017 18:24, schrieb DK7FC:

...today i drove to the company and got that high permeablic strip. http://www.iup.uni-heidelberg.de/schaefer_vlf/VLF/Powercore_H075-18_20mm_Thyssen.jpg

Quite a large amount!

To be continued...

73, Stefan

Am 13.11.2017 16:03, schrieb DK7FC:

Today i searched for suitable materials to build a iron band rod for a coil for 970 Hz.

I learned about kornorientiertes Elektroblech, https://de.wikipedia.org/wiki/Elektroblech or https://en.wikipedia.org/wiki/Electrical_steel

A normal 50 Hz transformer is using 0.5 mm plates. For higher frequencies there are thinner plates available.

I searched for a local company and quickly found this product catalogue:

http://www.lohse-ringbandkerne.de/uploads/downloads/Lohse%20Prospekt%20D_web_2017.pdf

Excellent! They offer 0.23 mm think plates.

Then i sent them an email request and later i had a telephone talk with the chief of the company. I asked if they have maybe even better materials and he said yes, they have a band of the type H075/18/20. This is a band which has a thickness of just 0.18 mm and it is 20 mm width. Since it is grain-oriented it matters how the B field passes through it.

He said that this special band is worse at 50 Hz but can be used to up to 4 kHz!!!!!!!!!!!!!!!!!!!!!!!!!!! So maybe this opens the frequency range from 4 kHz down to the lower ULF!!!! :-)

I got a good price, just 4 EUR for 1 kg but i have to order at least for 100 EUR so i will order 25 kg of that stuff! Already done!

My idea is to build a 0.5 m long rod. One piece of the band will then have a cross section area of 3.6 mm^2. I will need about 1000 to 1500 of these bands in parallel. This should fit into a PVC tube with an outher diameter of 80 mm. Very handy!

I'll keep you informed ;-)

73, Stefan

Jan 19th 2018

Hi VLF,

It took much longer than expected. Maybe 2/3 of the winter season is over now. Time to finally go the next step down to DC, another episode of the series "300 mA on..." :-)

Since 22:15 UTC a 300 mA carrier is running on 4470.1 Hz. A wavelength of 67114 m :-) The ERP is about 25 uW.

For the next few hours the tree will show the signal over the 3.5 km distance: http://www.iup.uni-heidelberg.de/schaefer_vlf/DK7FC_VLF_Grabber2.html

The carrier will run until 8 UTC (except the safety circuit trips dur to strong rain).

The new coil arrangement consists out of 6 (5 + 1/3) stacked buckets. Here a photo showing the arrangement for 5170 Hz (4 + 1/3): http://www.iup.uni-heidelberg.de/schaefer_vlf/VLF/coil5170Hz.jpg Now there is just one more bucket in the stack.

Before starting the next experiment on 970 Hz (probably next week), there are a few days now for a short message on the band.

Will it be possible to transfer a message over to Alex, on the 1990 km landpath? It is less than 30 wavelengths distance :-)

Also it would be a first detection and new lowest frequency for SQ5BPF in 920 km distance...

With some optimism i think 2 characters can be possible in 4 nights:

f = 4470.100000 Hz

Start time: 18.JAN.2018 16:00:00 UTC

Symbol period: 60 s

Characters: 2

CRC bits: 16

Coding 16K23A (NEW)

Duration: 13h20min [hh:mm]

Antenna current: 300 mA

73, Stefan

Jan 13th 2018

Paul Nicholson has news of a new EbNaut decoder:

Updated EbNaut decoder for Windows, now at version 0.8

http://abelian.org/ebnaut/software_ms.shtml

This version does 16K23A which is a useful polynomial

for short messages combined with a large CRC.

The Linux program is up to version 0.9 now.

http://abelian.org/ebnaut/software_linux.shtml

The only significant change is the use of DSW re-balancing

of the list decoder stack. This may reduce decode time

a little when using very large list lengths. It is most

useful when measuring the distance spectrum of a polynomial

where a degenerate tree often develops.

--

Paul Nicholson

Jan 7th 2018

New Amateur VLF record?

According to Google Maps, the distance between W4DEX (35.256133N 80.380048W) and DL0AO (49.430965N 11.79635E) is 7257.9 km. This is a bit further than to Cumiana (7173.4 km), so it looks like Dex and us are currently holding the world record. Well at least until Warsaw (7681.3 km) comes up with a decode...

https://klubnl.pl/rsgb_lf_group-archives/html/rsgb_lf_group/2018-01/msg00042.html

I'm not quite sure about the exact location of the VO1NA antenna. Assuming it is near Torbay, we get around 4606 km to DL0AO, which would make us third after RN3AUS (5810.5 km) and SQ5BPF (5096.6 km).

https://klubnl.pl/rsgb_lf_group-archives/html/rsgb_lf_group/2018-01/msg00069.html

https://klubnl.pl/rsgb_lf_group-archives/html/rsgb_lf_group/2017-12/msg00437.html

Hmm, feels good ;-)

Best 73,

Markus (DF6NM)

Jan 6th 2018

Hi VLF,

I'm back on air EbNaut with a new PA:

QRG: 8270.01953125

3 chars

60 sec/sym.

coding 16K21A

CRC 8

duration: 12h 16'

antenna current: 520 mA

Thanks a lot for reports.

GE.

73 de Riccardo IW4DXW

Jan 5th 2018

There is now more and more activity from across the Atlantic. W4DEX is trying with EbNaut as shown below:

Carrier on at 20:30

EbNaut starts at 22:30

8269.9 kHz

3 chars 16K21A CRC20

30 second symbols

Back to carrier mode after message is completes at 06:14 UT and will remain on until 14:00 UT

Dex