470 Hz


DL7NN
 

Dear OM's!

The team from DK7FC, DL3JPN and DL7NN asked themselves whether at a frequency of 470 Hz (638 km wavelength) the transmission of information by means of electromagnetic waves and moderate technical effort is possible.

The transmitter at DL0HOT in JO60IT was used for the test (DL3JPN - Steffen and DL7NN - Albrecht). The signal was generated with a GPS oscillator for 470.005 Hz and EbNaut modulator according to Paul Nicholson. A class D power amplifier from stage technology (Powersoft K20) was used as the power amplifier. The antenna consists of a 3 x 4 mm² wire to a ground at a distance of 1320 m (4,000 feet) with a DC loop resistance of less than 5 Ohms between the transmitter site and the remote ground. The series resonance was achieved with a capacitance of 44 µF. Due to the low impedance of the transmitting antenna of around 5 Ohms, no further adjustments to the output of the PA were necessary.

Stefan's (DK7FC) proven technology and experience was used on the receiver side (JN49IK - JO60IT distance 324 km). It has to be turned out that the H field at Stefan's location could not be used (due to the high level noise/sferics/a.s.o) and the evaluation of the signals had to be limited to the E field. But as final result, Stefan was succesfully able to decrypt two EbNaut messages. The first message on May 17, 2022 reached an Eb/N0 of 9.4 dB with 12 characters. Stefan was also able to decrypt the second message with 18 characters on May 21, 2022 with 3.9 dB Eb/N0. During this period, the high QRN was noticeable through numerous thunderstorms in the vicinity of the receiving station. Further carrier emissions on 05/18/2022 and 05/22/2022 were clearly visible in the spectrogram at DK7FC.


73
DK7FC, DL3JPN, DL7NN

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