Passive Microwave Transposer, Frequency Doubler for Detecting the Avalanche Victims

Electronic detecting methods for victims buried under the snow often show inconvenients such as wrong alarms (radar, radiometer). Another process, the passive transposer consists in providing people running such as a risk, with one or two cards of small size, very cheap, without any battery and containing an appropriate non-linear device (diode). In case of accident, the snow field is "lit" with an electromagnetic wave of frequency f. For instance, the detecting of double frequency 2f informs the rescuers of the presence and the place of a card. We describe a prototype working at f = 1250 MHz. The passive transposer range depends on the water content of the snow. In the worst case, that is when the snow is watery, the transmitter-receiver being on the ground, the maximum detecting depth is about 2.5 m.