This type of coil is used for large items. Ideal for searching wartime objects and metal objects at a solid depth. There is parameter data for finding objects with a thirteen-inch AKA 3kHz coil:
• ten kopecks - forty centimeters;
• twenty kopecks - thirty-five centimeters;
• a button made of copper - thirty centimeters;
• silver scapular - twenty-five centimeters;
• ten rubles - forty centimeters.
The coil successfully works with many multi-frequency metal detecting devices. If we compare with the coil 15 inches and 3 kHz, then the difference in the depth parameters is small. But only the thirteen-inch coil has a smaller diameter, so it’s more convenient to walk with it, easy to swing, suitable for the field where there is not a lot of litter. Low frequency allows you to "view" a large depth, does not respond to small objects.
Disadvantages of the coil:
1. If there is electromagnetic interference, the quality of work is reduced.
2. If there were small hits, false alarms are possible.
3. The parameters of discrimination and depth in heavily littered areas are reduced.
Advantages of the coil:
1. Large detection depth.
2. Excellent looking for large objects.