20 kHz is currently (2015) the largest possible frequency range among the coils offered by the Russian AKA company. Given that high-frequency signals respond best to small objects, such a detector is ideal for searching for coins, gold nuggets or flake coins on the edge. With such a high sensitivity, it is need to sacrifice the search depth - it is relatively small in these coils, since high-frequency signals tend to attenuate more quickly. At the same time, such detector can detect small objects at a greater depth than coils with a lower frequency. For example, a device of 20 kHz is guaranteed to “see” flake coin by 18 cm, and 7 kHz - only by 14 cm. The choice in favor of a 20 kHz coil should be made by those who are not going to work in heavily littered areas, since high sensitivity will allow to filter out metal debris and concentrate exclusively on useful objects. Difficulties in this case might arise only on the identification of large metal objects.