The VLF receiver in Warsaw (operated by Jacek/SQ5BPF) is currently turned off because the antenna had to be taken down.
This affects the VLF grabbers anf the stream on Nicholson’s page.
I hope to have the receiver running again in 1-2 months.
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.
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.
A video of the SAQ Alexanderson Day transmission on 9:00 UTC 20190630.
Received at SQ5BPF QTH Warsaw/Poland KO02md.
E-field active antenna, vlfrx-tools and Spectrum Lab receiver
Transmission at 9:00 UTC:
Transmission at 12:00 UTC:
SAQ transmision on Alexanderson Day, June 30th, 2019:
10.30 (08.30 UTC) Alternator is started
11.00 (09.00 UTC) Transmission of a message
13.30 (11.30 UTC) Alternator is started
14.00 (12.00 UTC) Transmission of a message
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
CRC bits: 16
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:
sq5bpf@jitter:/stuff2/sq5bpf/vlf_stefan2$ vtcat -p < stefan_2970_1 | vtfilter -a th=4 -h bp,f=2970,w=2200 > ../vlf_stefan2/pliktmp6 sq5bpf@jitter:/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:
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.
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
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!