RSDN stations are active again

After a long period of inactivity the RSDN stations are active again. Right now (12 october 2021) three frequencies are active: 11.9kHz, 12.65kHz, 14.88kHz.

This is a hyperbolic navigation system, which broadcasts a periodic carrier. More information is avaliable here:

For people interested in VLF this is a great test signal, whch can be used to check receiving equipment.

RSDN 2021

RSDN 2021

VLF grabbers reactivation at Warsaw / SQ5BPF

In 2019 i’ve written that the SQ5BPF grabbers will be  temporarily offline and should return in winter 2019. Unfortunately this “moment” got extended to august 2021.

Now, finally, I’m trying to reactivate them, The VLF antenna has been installed again. For now I’ve activated the ZEVS 82Hz and VLF 8270Hz grabbers. Because of changes in vlfrx-tools noiseblanker from versions 0.6 to 0.9, i will be trying to find the parameters for best reception, so please stay tuned, the grabbers might not be operating at their best right now.

The rest of the grabbers will be activated shortly.

As before, i’m recording the while 0-24kHz bandwidth, and keeping the recordings for a few days. They can be provided to interested parties upon request (for scientific reasons etc).

How Cave Communications works

Due to the ongoing (on 20 august 2019) rescue operation in the Wielka Śnieżna Cave in the Tatra mountains we decided to write about cave communications.

Thailand Heyphone
Thailand Heyphone

Rocks and soil attenuate radio signals well. Despite of this some means of communications in caves and mines are needed.

The attenuation rises with frequency. Normal VHF communications gear can’t be used, sometimes the distance can deteriorate to meters, depending on the geology and shape of tunnels. Of course cell phones are totally out of the question too. Shortwave radio behaves only a bit better.

Much larger distances can be achieved using low frequencies.

Continue reading “How Cave Communications works”

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:

Link to Paul’s VLF milestones list:

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”

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