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.
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.
Joe VO1NA transmitted on 21 december 2017 at 8270.0075Hz.His transmission was succesfuly received in Warsaw (RX Jacek/SQ5BPF), at a distance of about 5100km. This is the first succesful reception of a signal from Canada in Poland at 8270Hz.