Please join our new sister site dedicated to discussion of gold, silver, platinum, copper and palladium bar, coin, jewelry collecting/investing/storing/selling/buying. It would be greatly appreciated if you joined and help add a few new topics for new people to engage in.
The only reason I use a small coil on my TDI is to let me access tight spaces and to get around rocks and tufts of grass.
I find the detecting ability/sensitivity of these coils to be very near the same as the stock 12 inch.
EG, my infinium with the big DD will respond to a 0.15 g bit of gold at approx 6cm. The 3 x 7DD detects the same although the signal may be a bit shorter and sharper.
Pin 2-4 Power wire.
Pin 5 Shield from power wire.
Pin 1 is connected to the spare wire and shield.
The TDI PI coil whether Mono or Dual Field are changing between TX and RX function.
A DD coil however is using one coil as a TX (Transmitter) and the other coil as a RX (receiver) the connector is wired differently.
Detech 18" CC coplanar coil when wired as a DD coil, works well on the TDI and QED detectors.