The detectors on the beats are not very sensitive in the search for metals with a weak ferromagnetic properties, such as, for example, copper, tin, silver. To increase the sensitivity of detectors of this type is not possible, because the difference frequency - beating is hardly noticeable when the usual methods of indication. Great effect the use kartsovnik metal detectors.
An electronic finder, schematic diagram of which is shown in Fig.1, consists of a measuring generator, assembled on the transistor T1 and buffer stage is emitter follower, which is assembled on the transistor T2, separated by quartz from KV1 indicating instrument detector the diode D2 of the DC amplifier transistor T3. Load the SIC serves as a pointer instrument with a current total deviation of 1 mA.
Fig.1
Due to the high quality factor of the quartz slightest change in frequency of the measuring oscillator will result in a decrease in the total resistance of the latter, as can be seen from the characteristics shown in Fig. 2, and this, ultimately, is to improve the sensitivity and accuracy of the countdown.
Fig.2
Prepare to search is to adjust the generator frequency of the parallel resonance quartz equal to 1 MHz. This setting is performed by capacitors C2 (roughly) and a trimming capacitor C1 (for sure) about the lack of metal frame items. Since quartz is an element of communication between the measuring and indicating the parts of the device, its resistance at the time of resonance is high and the minimum reading of the galvanometer indicates a precise adjustment of the device.
The rest of the operation does not differ from that of the metal detectors on the beat. The sensitivity level is adjusted by the variable resistor R8.
Feature of the device is annular frame L1 made of a piece of cable. Core of the wire is removed and instead proderzhivaetsya 6 turns of wire type PEL of 0.1-0.2 length of 115 mm. frame Design and pin order is shown in Fig.3. Such a frame has a high q and a good electrostatic shield. The rigidity of the frame is ensured by placing it between two discs of plywood or Micarta with a diameter of 400 and a thickness of 5-7 mm.
Fig.3
The device can be used transistors KT315B,silicon reference diode SA. detector diode type D9 with any letter index. The crystal frequency may be in the range of frequencies from 900 kHz to 1.1 MHz. Cable RK-50.
Literature
Publication: N. Bolshakov, rf.atnn.ru