Antenna Noise Bridge Low Frequency Converter 60 kHz Receiver VLF Receiver 198 kHz Converter
50 & 70 MHz Converter Audio Oscillator MSF Clock Tunable Audio Notch Filter Programmable Chime
Antenna Tuner Speech Compressor Two Tone Oscillator Sound Meter 136 kHz Crystal Calibrator


136 kHz DX
Weather forecasting
144 MHz DX by forecasting Auroras

Get 30 hours notice of auroras, and possible VHF openings in the UK, by monitoring the strength of U.S.A. VLF signals on 17.8 or 21.4 kHz. During the day look for a solar flare causing a sudden change (usually an increase) in signal strength of about 6 dB from the usual night time level, and recovery after about 1 hour. Get the receiver working on 60 kHz and then retune with additional capacitors, C2 + 180 pF, C4 + 47 nF, C8 + 47 nF, C9 + 47 nF, C10 + 100 nF. You can just about hear the USA stations in the UK with the built-in ferrite rod antenna, but you will need a few metres of external antenna to detect changes in signal strength. You will not be intercepting any messages from these U.S. Navy transmitters, just monitoring the level of their 24 hour/day world wide signals.
You can use this circuit to feed a chart recorder or A/D converter.


136 kHz DX and Weather Forecasting

Receive amateurs on the 136 kHz band or receive weather facsimile forecasts on 131.8 kHz (France) or 134.2 kHz (Germany). The modulation is white + 150 Hz, black - 150 Hz. Get the receiver working on 60 kHz and then retune with capacitors, C4 470 pF, C7 180pF, C9 2200pF and T4 2N2369 or equivalent high speed transistor.
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