GPX 6000 technical information page

[Chet]

Small nugget coils

When a nugget is energized by a fast magnetic field from the discharge of a high current pulse of a pulse induction transmitter it answers back with a fast dying feeble magnetic field.

The duration of the signal response time in small nuggets is less than 15 microseconds (0.000015 seconds).

Coils must be sensitive to capture this fast decaying feeble signal. The type of wire, wire size, wire insulation, turn spacing and other construction techniques affect the sensitivity and overall performance. If all of these variables are the same then Flat Spiral wound coils are more sensitive than bundle wound.

For small nuggets the coils must be smaller to focus on a small shallow area to receive this feeble signal. Small coils do not have enough room for Flat Spiral windings. A compromise is to have layers of Flat Spiral windings. The GPX 6000 11” Mono coil appears to have two layers of Flat Spiral windings.

Attached are two examples of Flat Spiral windings; the 18” has close side-to-side turns; the large 40” has Flat Spiral windings that have 0.5” spacing between turns. A spacing greater than 6 diameters of the wire size greatly reduces the opposing magnetic current losses between side-to-side turns.

The blue Basket weave coil is a carry-over from the early days (1920’s) of AM radio. It has some characteristics that are desirable. But it is difficult to make and in my opinion no noticeable improvement in performance.

The performance of small nugget coils for the GPX 6000 will be determined by users field reports.

 

[Aug]

Chet, do you have any resources for the characteristics of basket weave coils? I've often wondering about different windings like this. Thanks.

 

[Chet]

The following is copied from Wikipedia, the free encyclopedia
at: https://en.wikipedia.org/wiki/Basket_winding

“Basket winding made with Litz wire in an IF transformer
Basket winding (or basket-weave winding or honeycomb winding or scatter winding) is a winding method for electrical wire in a coil. The winding pattern is used for radio-frequency electronic components with many parallel wires, such as inductors and transformers. The winding pattern reduces the amount of wire running in adjacent, parallel turns. The wires in successive layers of a basket wound coil cross each other at large angles, as close to 90 degrees as possible, which reduces energy loss due to electrical cross-coupling between wires at radio frequencies.

Purpose
The basket winding method is used for coils designed for use at frequencies of 50 kHz and higher to reduce two undesirable side effects, proximity effect and parasitic capacitance, that arise in long parallel segments of current-carrying wire.

The proximity effect is caused in a wire by the magnetic field from current flowing in nearby parallel wires, such as other loops in the same coil. If two adjacent wires carry a current in the same direction, then the effect is felt in both – the magnetic field of the nearby wires causes current in each wire to be concentrated in a small region on the wire’s surface farthest from the adjacent wires. The concentration of current along a small portion of the conductor increases the wire’s resistance and hence increases energy loss. At medium and high radio frequencies the increased resistance of the inductor can increase the bandwidth of tuned circuits and reduce the circuit’s frequency selectivity, or Q factor.
Parasitic capacitance is the consequence of parallel turns of wire acting as capacitor plates, storing charge between adjacent wires. The parasitic capacitance can cause the coil to become self-resonant at one or several frequencies, which interferes with the intended tuned resonance and blocks and reflects current at the self-resonant frequency.

Unfortunately basket-weave coil winding increases the physical size of the coil, which increases leakage inductance.”

In my opinion Basket weave coils wound for a metal detector do not form as good of a magnetic field as a Bundle or Flat Spiral wound coil. They are larger and have more resistance which reduces the transmit efficiency

 

[Teemore]

Thanks Chet ...... if readers haven't learnt something in the last few days about coils they're not really trying.

 

[Ubutey45]

Small nugget coils

When a nugget is energized by a fast magnetic field from the discharge of a high current pulse of a pulse induction transmitter it answers back with a fast dying feeble magnetic field.

The duration of the signal response time in small nuggets is less than 15 microseconds (0.000015 seconds).

Coils must be sensitive to capture this fast decaying feeble signal. The type of wire, wire size, wire insulation, turn spacing and other construction techniques affect the sensitivity and overall performance. If all of these variables are the same then Flat Spiral wound coils are more sensitive than bundle wound.

For small nuggets the coils must be smaller to focus on a small shallow area to receive this feeble signal. Small coils do not have enough room for Flat Spiral windings. A compromise is to have layers of Flat Spiral windings. The GPX 6000 11” Mono coil appears to have two layers of Flat Spiral windings.

Attached are two examples of Flat Spiral windings; the 18” has close side-to-side turns; the large 40” has Flat Spiral windings that have 0.5” spacing between turns. A spacing greater than 6 diameters of the wire size greatly reduces the opposing magnetic current losses between side-to-side turns.

The blue Basket weave coil is a carry-over from the early days (1920’s) of AM radio. It has some characteristics that are desirable. But it is difficult to make and in my opinion no noticeable improvement in performance.

The performance of small nugget coils for the GPX 6000 will be determined by users field reports.

Where ive been detecting lately the nuggets mustv been very insensitive and lazy as they havent been answering back to much lately lol good article