Hi Nicolas
Perhaps you can try other frequencies but you must remember that the "heart" of the circuit are L1, C1 and C2, with these values and the parasitic capacitor there is only one working frequence. If we change L1 or C1 or C2 or all these together I'm not sure that the "phenomenon" is detectable. However, it is always useful to experiment with new solutions.
Best Regards
Perhaps you can try other frequencies but you must remember that the "heart" of the circuit are L1, C1 and C2, with these values and the parasitic capacitor there is only one working frequence. If we change L1 or C1 or C2 or all these together I'm not sure that the "phenomenon" is detectable. However, it is always useful to experiment with new solutions.
Best Regards


it's another version of my Lrl more sensitive but less difficult to build. The oscillation comes from a CD4046 and we measure the phase change between the VCO and the output of the amplifier stage (TR2-TR3 and TR4). As antenna you can use a stylus or (better for me) a coil antenna. The capacitors C8 and C9 are connected in series for a single 0.5 pF capacitor (I think difficult to find). The power stage is the same of the other Lrl. In this simplified version there is only a led but is better to use more leds, I use a LM3914 to drive ten leds. The frequency is in the range 2.8 - 3.0 Mhz with the P1 cursor close to + 12V. Also the P2 cursor is close to positive and this means a small signal to input amplifier stage.
I forgot also C18, it's 4.7 nF.
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