Basket weave search coil

[James]

I would like Carl your opinion on basket weave search coil. I think by wind this coil one should be able to reduce the capacitance between the windings. I would think it should be able to reduce the search time to 8us or less. Thank you for your opinions an time

[Carl-NC]

Basket weave will certainly minimize the C but it's possible to achieve 8us and even 6us with a scramble-wound coil using PVC insulation. Look at better FETs (esp SiC type) that don't avalanche and a faster recovery preamp.

[Qiaozhi]

Basket weave will certainly minimize the C but it's possible to achieve 8us and even 6us with a scramble-wound coil using PVC insulation. Look at better FETs (esp SiC type) that don't avalanche and a faster recovery preamp.

I agree with Carl.
Having built and tested both spider and basket weave coils I found that using simple scramble-wound PVC insulated hookup wire gave as good results without the pain of a difficult construction method.

[green]

I made a few scramble-wound coils when I first started making coils. Then I read adding a MUR460 diode in series with the coil would speed the decay. Tried making basket coils thinking they would be fastest. Read about spiral wrapped coils and tried one. Was surprised how close spiral wrapped is to basket coil. Including a picture of basket vs spiral wrapped. When I first started, I didn't know to measure resonance so don't have any measurements for scramble-wound. Maybe someone could post some specs for their scramble wound coils. Picture is coil without lead, adding lead typically lowers resonance to around 1MHz.

[bbsailor]

I made a few scramble-wound coils when I first started making coils. Then I read adding a MUR460 diode in series with the coil would speed the decay. Tried making basket coils thinking they would be fastest. Read about spiral wrapped coils and tried one. Was surprised how close spiral wrapped is to basket coil. Including a picture of basket vs spiral wrapped. When I first started, I didn't know to measure resonance so don't have any measurements for scramble-wound. Maybe someone could post some specs for their scramble wound coils. Picture is coil without lead, adding lead typically lowers resonance to around 1MHz.

Green,

The coil shield adds Distributed Capacitance which is a very complex calculation. To get a good value for distributed capacitance just measure the coil self resonance frequency without the shield and calculate the capacitance, then do that again with the shield and calculate the capacitance. My experience is that the distributed capacitance of the shield adds about one quarter of the measured coil to shield capacitance measured between one coil winding and the shield. I chose to use Scotch24 for a shield because it is a fine wire mesh and adds less capacitance than a solid shield materiel due to less surface area.

The key is to know in which direction each variable you use moves to ensure that the final result moves all these variables in the same direction to optimize your coil for the desired target.

The purpose of the diode is to minimize the capacitance the coil sees upon discharge from the capacitance in the MOSFET coil driver and other TX circuit components. The coil still sees all the RX circuit effects including the damping resistor value, coil capacitance, and coax capacitance.

Joseph J. Rogowski

[lucifer]

I made a few scramble-wound coils when I first started making coils. Then I read adding a MUR460 diode in series with the coil would speed the decay. Tried making basket coils thinking they would be fastest. Read about spiral wrapped coils and tried one. Was surprised how close spiral wrapped is to basket coil. Including a picture of basket vs spiral wrapped. When I first started, I didn't know to measure resonance so don't have any measurements for scramble-wound. Maybe someone could post some specs for their scramble wound coils. Picture is coil without lead, adding lead typically lowers resonance to around 1MHz.

Hi green,
Are you sure about your flat spiral coil calculations/measurements? 8.9pF (no shield) for that coil seems a bit optimistic to me.

[green]

Hi green,
Are you sure about your flat spiral coil calculations/measurements? 8.9pF (no shield) for that coil seems a bit optimistic to me.

Having read, need to add a spacer between spiral windings to make a fast coil I expected higher capacitance with no spacing. 333uH and 2.92MHz calculates 8.9pf. Readings for the spiral were closer to the basket than I expected. Maybe someone else has tried with different results or has some comparison reading for spiral (with spacer) and spiral (with no spacer).

The basket coil is a little better, about as easy to make for me if making a mono coil. Spiral wrap works better for making figure8 Rx with separate Tx.