ULF 2970.1 reception record

Stefan DK7FC transmitted at 6 aptil 2019 20:25 UTC at 2970.1Hz. The TX power was 487W into a 1130m ground dipole antenna. The ebnaut transmission parameters were:

f = 2970.1 Hz
Start time: 06.APR.2019 20:25:00.3 UTC
Symbol period: 6 s
Characters: 7
CRC bits: 16
Coding 16K21A
Antenna current: 2.4 A
Duration: 02:04:48 [hh:mm:ss]

The signal was received by Jacek / SQ5BPF in Warsaw/ Poland KO02md, at a distance of 976km!

After the filtering and noise blanking was optimised, the signal could be decoded:

[email protected]:/stuff2/sq5bpf/vlf_stefan2$ vtcat -p < stefan_2970_1 | vtfilter -a th=4 -h bp,f=2970,w=2200 > ../vlf_stefan2/pliktmp6

[email protected]:/stuff2/sq5bpf/vlf_stefan2$ vtblank -v -d0.0007 -a20 -t 50 < pliktmp6 | vtmult -f 2970.1 | vtresample -r 240 | vtresample -r 10 |vtraw -oa | ebnaut -dp16K21A -r10 -c2 -v -k16 -S6 -N7 -PS -L 50000

vtblank: selected channel: 1 = -:1
vtblank: channels: 1, sample_rate: 48000
vtblank: hfactor: 0.000e+00
vtblank: afactor: 20.000
initial reference phase -89.4 amplitude 7.496e-04
phase 0 0 0 0 0
vtblank: end of input
vtblank: dropsum 0 64750004, nfp 359999999
vtblank: dropfactor 0 1.799e-01
found rank 14143 ber 4.2548e-01 Eb/N0 -2.5 M -2.143712342e-02 ph 0 0,0,0,0 [DK7FC/P]
carrier phase: -10.6 deg
carrier Eb/N0: -0.4 dB
carrier Es/N0: -15.33 dB
carrier S/N: 15.63 dB in 133.5 uHz, -23.11 dB in 1Hz, -57.09 dB in 2.5kHz
elapsed 92

The message was: DK7FC/P

Link to Stefan’s email:



Record distance for a VLF transmission from an earth dipole antenna.

Recently we’ve done a successful  transmission from an earth dipole on 8270 Hz.

This is the first amateur transmission on VLF from Poland which has been received in another country. This is also the record distance for a transmission using a ground dipole antenna – over 1330 km.

Link to Paul Nicholson’s post about it: https://klubnl.pl/rsgb_lf_group-archives/html/rsgb_lf_group/2019-03/msg00025.html

Link to Paul’s VLF milestones list: http://abelian.org/vlf/amateur-radio/

This is probably the first VLF signal which has been transmitted from Poland after World War II. We are not aware of any military or other transmissions. Before the war we had the Babice Transatlantic Radiostation (callsigns AXO/AXL/SPO/SPL), which was similar to Grimeton/SAQ.

VLF transmit tests from a ground dipole

Encouraged by our last experiments with ground dipoles we decided to do a transmit experiment with this antenna on VLF 8.270kHz, 36km (36000m) wavelength. Thanks to  Fab LAB Trójmiasto we had a great location on the see on a cliff near the Baltic Sea in Gdynia. Our goals for this experiment were:

  • Try transmitting from a ground dipole on VLF
  • Assess the field strength near the sea
  • See if it is possible to reach greater distances with relatively simple equipment and low power.
  • Test a broadband transformer for VLF-LF-MF

Continue reading “VLF transmit tests from a ground dipole”

Complete archive of 20 years of the RSGB LF Reflector

The RSGB LF Reflector is the most important group for low-frequency enthusiasts. For many years list members have been witnesses to milestones in the 136kHz, 73kHz, 500kHz, 472kHz, VLF and lower bands. Many posts have great historical significance.

When we created the KLUBNL.PL website, one of our most important goals was to create a publicly available archive of this list: https://klubnl.pl/rsgb_lf_group-archives/html/rsgb_lf_group/

In the beginning this archive spanned from 2014 up to now. Recently we imported archives kindly donated by Dave G3YXM and Markus DF6NM. Thanks to them the archive now spans from February 1999. 20 years of radioamateur longwave (and medium-wave) radio history!



End of NDB BIA on 474kHz

Sadly the NDB BIA on 474kHz in service at Rzeszów Airport has been turned off.

For many years the carrier at 474kHz and the sidebands at 473kHz and 475kHz were used by polish radioamateurs to check their 630m equipment. Foreign radioamateurs used this NDB to judge the propagation to Poland.

This will change the way we work in the CW segment in the 630m band in Europe. Up to now we had to use 472-472.7kHz or around 473.5kHz, and a narrow filter was necessary. After BIA is switched off we can use the whole 472-475kHz segment, also with wider filters.

NDB BIA 474kHz antenna

VO1NA on 8270Hz received in Warsaw

Since a few days one can see a faint line on 8270.0075Hz. This is transmitted by Joe VO1NA from Canada. The distance to Warsaw is 5100km!

Spectrogram with normalized amplitude:

I have received Joe VO1NA in 2017 when he transmitted ebnaut:



You can also see a very strong signal from Stefan DK7FC on 8270.0Hz


SAQ Christmas 2018 transmission on 17.2 kHz

Christmas  transmission from SAQ on 17.2kHz, 24 december 2018 8:00 UTC

Received at SQ5BPF QTH Warsaw/Poland KO02md.

E-field active antenna, vlfrx-tools and Spectrum Lab receiver

The message was:


630m transmit experiment with a baloon lifted antenna

Autumn and winter are great for experimenting on the medium wave band. We’ve tried  a 150m baloon-lifted antenna.

Our objectives were:

  1. To see how a quarter-wave vertical works at 472kHz
  2. Testing the hydrogen generator
  3. Determining how much weight can be lifted by a 1m diameter baloon, and how it will behave in the wind.

The results are encouraging. This is an analysis of the experiment:

  1. During the experiment we had very strong wind with gusts up to 15m/s. This, combined with rain, damaged the baloon. In these circumstances a kite would have probably been better. Unfortunately we couldn’t do the experiment when the weather was better. During high winds a string support is needed for the base antenna line. At first we’ve tried a fibreglass/epoxy fishing rod, but the forces were too strong and we had to change it for a wooden pole.

2. It’s best to use a copper-covered welding wire. It’s strong enough and very light. Unfortunately aluminium wire  is not strong enough. It’s also best not to use wires covered in isolation, because of their additional weight.

3. If the antenna is to be used during the night, there has to be some means to show the baloon position. We think that it is sufficient to use a simple pulsating LED light powered by a watch battery.

4. The antenna was tuned to resonance with an antenna analyzer by varying the antenna length. This way we were able to quickly determine the correct length of the wire. The SWR varies with the antenna position relative to earth, the range is about 1.3 – 2.3.

5. For ground we used an earthing rod in a 13m deep well. The resistance of this ground is 37Ω at 70Hz, at 472kHz it is probably much higher. The antenna impedance was about 200Ω, so we needed to use a 1:4 transformer to match the antenna. The theoretical impedance of a quarter-wave vertical is around 35Ω, so the rest (200Ω-35Ω=125Ω) is due to loss. This calculates to antenna efficiency around 15%, so we need around 15W to get to the 1W EIRP legal limit.

6. The signal was received by many european stations. Unfortunately the baloon was destroyed by very strong wind and rain before the transatlantic propagation time.

7. The optimal way of generating hydrogen in an amateur setting is the reaction betweem aluminium and NaOH (sodium hydroxide) solution  One should not use aluminium dust or fine filings, because the reaction is too quick and overheats. Aluminium soft-drink cans are covered with paint, and the reaction goes too slowly in this case.  Larger aluminium  shavings are optimal. NaOH can be purchased as pellets used for unclogging pipes. The generator consists of three parts: a hydrogen generator (bottle with the NaOH solution and aluminium), a scrubber (bottle with water that the gas passes through) and preferably a dessicator (third bottle with solid dessicant). You should wear protective gear at all times, and take measures not to harm yourself. A concentrated NaOH solution will cause permanent damage to eyes and the rest of the body. If in doubt, consult a chemist  (both of the founders of klubnl.pl have a masters degree in chemistry).