I have been pre-occupied these last few months with metal detectors. Despite owning 6, I was recently disappointed on a trip to the Golden Triangle, when the ironstone ground I had researched as a very likely gold area, was too hot for any production-line detector. I did however find small gold nearby with my Whites GMT. Since the introduction of vlf and Pulse Induction in the 80's, the older technologies of BFO (beat frequency oscillator) and IB (induction balance) have been ignored. So I have revisited these technologies with reasonable success. My intent is to scour all the ironstone gold areas where the Minelabs and others cannot even operate due to ground noise. This was my first etch. It is a "Matchless"IB metal locator, freely available online. On the right is my first detector. It will "see"a 5c piece at 15cm and 2.4g gold at 8cm, with a 15cm coil. Iron makes it go silent and non-ferrous materials have different tones.. For iron relics simply tune to the other side of the null point. The transistor of the circuit is taped to the radio at the strongest signal point, and around 1000khz. It has 2 operating frequencies-32 or 48 khz. This board is an Induction balance detector, with a built in AM receiver and amplifier circuit. I made a couple of mistakes, but it will eventually be another very handy unit. The 2 coils are partly over-lapped to produce a sweet spot with high signal. Ferrous is virtually ignored whilst non-ferrous can be heard on multiple and over-lapping signals. It can also discriminate by tilting one side of the coil towards the ground- either the ferrous or non-ferrous sensing side. I can get a faint signal from 5c at 25cm and 50cm for a 50c peice. It operates at 110 khz. Also I have an assembled Surf-Pro PI DD board, with a ML 10x5 DD coil to set up. This will have 18650 batteries, a charge controller and a 1.5w solar panel. Hopefully by starting with the ML coil I will be able to get this working good. Garret Infinium, Whites Goldmaster, 2 cheapies. 2 more at my Ex's.