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: http://www.vlf.it/alphatrond/alpha.htm

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”

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:

https://klubnl.pl/rsgb_lf_group-archives/html/rsgb_lf_group/2019-04/msg00042.html

 

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.

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!