[vlf]

I am a radio amateur and my other hobby is the metal detecting.
I built this modificated PDK 2.1 (circuit and picture in appendix). My PCB is 70*30mm without LM371 circuit instead I use a separate step down pcb (18V input and adjust 9.0V out regulated). The inductance of the coil is 286 mikrohenry d70mm with 50 turns. I can switch several capacitors paralel to the coil for extr tuning. The PDK is ready it works for the first test outdoor. (but not with buried metal)
Test result: The sensitivity is very poor. After tuning the led shines if I touch the poti with the hand but when I turn the coil near metal no signal appears. I transmitt a VLF signal sinus wave into a short wire antenna in the range of 70-120khz no reaction farther than 15cm from the coil.
Anybody help?


Thanks in advance


VLF