Today, I heard about some remarkable experiments at 270Hz using earth-electrode antennas.
Hello OM'S!
After successful 470 Hz transmissions, we (DK7FC, DL3JPN and DL7NN) tried to push to even longer wavelengths. The next goal is/was 270 Hz, i.e. 1111 km wavelength. First, the existing ground loop at the transmitter site had to be resonated by enlarging the series capacitor. After all, 116 µF was required.
According to the wavelength / 2 PI definition, in this case we reach the far field after 178.8 km. The distance between our locations is 324 km, which is far field by definition. Since Stefan's reception was exclusively in the E-field, a simple coupling of the magnetic field could be ruled out. After an integration time of 4.5 hours, Stefan achieved a carrier S/N of 17.84 dB in a bandwidth of 62.2 µHz. Even in the spectrogram heavily overlaid with summery QRN, the carrier was still visible. For comparison, the 270.005 Hz transmission at a distance of 4 km from the transmitter on the DL0HOT grabber with a bandwidth of 3.8 mHz.
This may have been the first successful detection of far-field SLF transmission by radio amateurs.
73
Albrecht
DL7NN
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