Whites AF108 detector coil question

[GeoMax]

Hi Forum,
I study the schematic of the Whites AF108 mine detector and have a question in regards to the search coil. From the circuit diagram, it seems that the search coil (TX/RX), connected at SK1 & SK2, is a center-tapped coil. Is it? Has someone additional information about the search coil and/or the specification?
I found an operator manual in the Internet, but there must be also a service manual or an add-on to the operator’s manual available. Does someone has it and can post it or maybe has information’s about it?
Thanks.

[Skippy]

It looks like the drive circuit is identical for both coil outputs, which would suggest both coils are identical. I've looked online, and the coil appears physically like a mono coil, so it's probably two windings together, bifilar style. And mine detectors are known to use bipolar pulsing, in order to reduce the chance of accidentally triggering the mine.

[Carl-NC]

Yes, the 108 is bipolar and uses a bifilar-wound coil. I have a 108 and will try to dig it out and see if it includes a service manual.

[Qiaozhi]

Does this help? See attachments.

[GeoMax]

Hello to all,

thanks all for your reply. It helps a bit for sure. It would be interesting to get more specific information on the coil etc.

Thanks

[GeoMax]

In the meantime I found 3 manuals about the AF108. But no details about the coil. Anyway attached are the documents I found. In one of the manuals is a referal to other additional manuals. Maybe someone has them and can post it here too.

[Carl-NC]

I pulled out my '108, each coil measures 181uH and is brought separately to the control box. That is, there are 4 coil pins in the connector. My unit has no documentation, and a note inside says that the battery box is missing. Otherwise, it's brand new.

[GeoMax]

Hi Carl,

thanks for the information.

[Skippy]

Remember , when Carl says each coil measures 181 uH , that is taken with the other winding unconnected. So the wires in the measured coil are separated by plenty of 'air space' , giving a much lower inductance reading.
A more technically useful figure would be the total inductance of all the coil windings, when they are connected in series. That would then help reverse-engineer the number of turns, with the aid of the 'Coil Calculator' program.
So for example, the total winding L may measure up as 1000 uH. You may be thinking that each half of the winding would thus measure 250 uH. But it actually measures 181 uH, because of the poorer magnetic coupling between each turn of the coil.