The converter will work reasonably well from a few kHz up to around 100kHz. Of course the choice of crystal depends on what is in the junk box. The circuit consists of a low pass filter (see yellow choke at bottom) feeding into an SBL1 double balanced mixer connected "back to front" with the IF port as the main RF input, a 12MHz crystal local oscillator, a 2N2904 IF pre-amp feeding the output at 12.0172MHz (12MHz + 17.2kHz) into the FT817 in CW mode. The converter below was built to use with my FT817, but it will work with most SW receivers. Today the same station and antennas are preserved as a UNESCO World Heritage site some 80 years later. On Dec 1st 1924 it first transmitted with the SAQ callsign on 16.1 kHz, but this was later changed to 17.2kHz on which frequency it operates occasionally today. The antenna consists of six 127m high antenna towers placed at intervals of 380m with the 46m cross-arms carrying the eight copper antenna wires. The 200kW transmitter was, and still is, unusual as it consists of an AC generator (alternator). Transmissions on VLF are rare today as most remaining VLF stations use These special commemorative CW transmissions happenĮvery few months. On Christmas Eve 2006 I wanted to try to copy the VLF morse code signals from SAQ at Grimeton
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