What is the search for the best coin detectors? BFO? PI? And IB's?

[yhl]

What is the search for the best coin detectors? BFO? PI? And IB's?

[mikebg]

What is the search for the best coin detectors? BFO? PI? And IB's?

Your question needs two answers:
1. Most deep detecting search coil for coin size targets is IB (Separate TX and RX coils placed in induction balance). This is valid for all kind metal detectors: BFO, CW and PI.
2. Most deep detecting principle for coin size targets is CW (continous sine wave) having narrow band receiver. It should operate in a frequency of VLF band, preferable 14kHz. The bandwidth of RX should be no more than 16Hz.