125. General

a. Types. In World War II the German Army used eight different models of metallic mine detectors. One of these the Stuttgart 43 (par. 133), was developed to detect a radioac-tive substance called Tarnsand laid with nonmetalic mines. Except for the Stuttgart 43, which uses Geiger-Müller tubes, the German mine detectors represent only two princples of operation – the heterodyne and the induction bridge.

(1)

Heterodyne. The heterodyne type employs two high-frequency (HF) oscillators which produce an audible beat note. One oscillator has a tunning condensor for varying its frequency and has as its inductance a search coil in the search head. The other oscillator has a fixed oscillation. The variable oscillator is synchronized with the fixed oscillator to give a beat note. Proximity of the search coil to metal changes the inductance, producing changes in frequency of the audible beat note.

(2)

Induction bridge. The induction bridge type employs a single low-frequency (LF) os-cillator, the output being fed through an induction bridge to an amplifier. An alter-nating current passed through the detector search coils in the search head sets up a magnetic fields. If a metallic object is pressent in the soil within this magnetic field, the metal changes the character of the path of the field, producing an audible response in the headset.

b. Models. The large number of models of German mine dectectors reveals a lack of standardization caused by the fact that several independet agencies developed detec-tors for the German Army. The following paragraphs describe the more frequently en-countered models in details while the models produced in limited quantities are only brief-ly described.