Radio transmitter carried by person buried alive - operates on frequency in MHZ range at which body has half-wave resonance

摘要

A person in danger of being buried alive carries a small radio transmitter by which he can be located using a search receiver. The frequency is chosen, in the range 50 to 100 MHz, at which the human body exhibits a half-wave resonance, depending on the dielectric constant of the surrounding medium. The transmitter (S) is worn near the waist and connected to a centre-fed half-wave wire dipole. The dipole arms (s) are coiled up to reduce their physical length (1) without seriously changing electrical length, and arranged to be vertical when the body is upright. Since the body has a broad, damped resonance at the transmitter frequency and the dipole is closely coupled to it, radiation is largely independent of body position, even when lying on top of the dipole.