Null on coins in center of DD coil issue.

[SVEN1]

Question regarding DD coils.
I have a factory made DD coil.
In all metal mode the detector with a fast sweep, the nulling of a coin or gold ring target sound when the coil center passes over it is guess acceptable.
In disc mode, coin gold ring targets produce a double beep. Once before the coils center brace and again after the coil center passes. Increasing recovery speed narrows
the distance to the center braces edge, nulls, then upon exiting the braces other edge sound off again. Pinpoint feature of the detector is useless at it pinpoints in the middle, between the coils outer edge and coil center brace.
In either side of the coils center brace.

So just wondering if was just not nulled right at the factory or?
Over all it's not especially nice to hunt in disc mode.

[Davor]

Most probably it is a problem of phase reversal, not nulling.
I guess you connected Rx coil reversed. Swap the Rx wires going from coil connector to a preamp, and it should be fixed.

[Koala]

Agreed. Home made DD I don't bother marking the start of my windings. If all metal works backwards or discrimination gives a double beep I reverse either the TX or RX connections and it works fine.

Concentric coils are more critical.

[Skippy]

Ditto. Classic reverse polarity symptoms. Which is wrong, TX or RX, is up to you to decide, based on shield/screen connections etc.

[SVEN1]

It's not a coil I made it came with a detector I received.
I will contact the company.

[Koala]

It's not a coil I made it came with a detector I received.
I will contact the company.

Surprised it passed quality control. What brand is it ?

[SVEN1]

No particular brand currently on the market to be concerned with.
I just wanted to get some verification that I suspected a coil issue.

[Davor]

In case either of the coils has both leads unconnected to the shield, you may swap them in a connector. It is odd for a factory coil to be reversed.