Broadband detector for miniature, e.g. spying HF transmitters - uses AC antenna voltage as input transistor control voltage

摘要

A small convenient electronic measurement device enables broadband detection and location of miniature transmitters (e.g. miniature espionage devices) and h.f. fields in the range 1MHz to 1GHz. High frequency fields can be detected with the device without frequency tuning. The device produces an audible and/or optical indication of the presence of the detected field. It can be operated single-handedly. The sensitivity is less than 0.5 mV. This enables weak sources to be located up to a distance of two or three metres. The a.c. voltage on the antenna causes a change in the control voltage of the input transistor voltage variation is amplified by the next transistor and displayed.