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Hi everyone,
some friends gave me three identical concentric coils from some chinese BFO detectors that no longer works due to a wather leakage.
The coils have these values:
TX: 5.2mH, 25Ohm
RX: 9.7mH, 37Ohm
They are in perfect mechanical and electrical conditions.
I made an oscillator like the one on the ITMD3 Raptor project and it works. I coupled the TX with a 47nF capacitor and the RX with a 22nF+3.3nF capacitance. Given that the oscillator is supplied with 9V, the signal straight from the RX was about 2Vpp!
I gave a look at the original pcb, even if it was completely corroded I manage to identify the RX circuit, implemented with an OP27, but I culdn't figure out the gain. What I noticed tho was that there was some kind of feedback from the TX to the RX, and I can oly suppose that was used to fine null the RX signal. But come on, 2Vpp, isn't it too much on the RX side?
Now I wander if this is just a ****ty coil or there is some more advanced way of driving it. Especially if there is some smarter way to implement the negative feedback from the TX to the RX rather than just use an RC based filter
some friends gave me three identical concentric coils from some chinese BFO detectors that no longer works due to a wather leakage.
The coils have these values:
TX: 5.2mH, 25Ohm
RX: 9.7mH, 37Ohm
They are in perfect mechanical and electrical conditions.
I made an oscillator like the one on the ITMD3 Raptor project and it works. I coupled the TX with a 47nF capacitor and the RX with a 22nF+3.3nF capacitance. Given that the oscillator is supplied with 9V, the signal straight from the RX was about 2Vpp!
I gave a look at the original pcb, even if it was completely corroded I manage to identify the RX circuit, implemented with an OP27, but I culdn't figure out the gain. What I noticed tho was that there was some kind of feedback from the TX to the RX, and I can oly suppose that was used to fine null the RX signal. But come on, 2Vpp, isn't it too much on the RX side?
Now I wander if this is just a ****ty coil or there is some more advanced way of driving it. Especially if there is some smarter way to implement the negative feedback from the TX to the RX rather than just use an RC based filter
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