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Extend your coverage down to 10 kHz with this Very Low Frequency Receiver, 10 - 150 kHz, direct conversion for morse, 50 k ohm input impedance for 15 m antenna, needs 12 V at 10 mA, 4 x 7 x 13 cm, 250 g.

"very interesting to hear stations on VLF", FR in High Wycombe, Bucks.
"excellent little set", THR in Worthing.
"neat and works very well", CGM in Jersey.

This fun-to-build kit used to include all parts, tinned drilled fibre-glass pcb, case, connectors, screws etc as well as detailed assembly and operating instructions including circuit description and diagram.
Please e-mail for any extra parts now neeeded.

img2013/4k vlfatu.gif Take the output from the emitter of T1 in the 100 - 600 kHz Converter, via a 100 nF capacitor. Add 33 mH in series with L3 to tune down to 15 kHz. This works well with a short antenna.
Use an inexpensive 40kHz transducer to the antenna input to detect high frequency sound from gas leaks, bearings running dry or bats - attract them by throwing a tennis ball high into the air at dusk.