Helical coil-shaped radio antenna is for apparatus sending data telegrams at given frequency and its vertical height and coil diameter are small compared to one quarter wavelength

摘要

The cyclic data telegram transmitter has a frequency of 868 mhz. The spiral antenna (1) can fit inside the housing of the radio set. The height and diameter of the spiral are small compared to lambda/4 - approximately 86 mm at a frequency of 868 mhz. The spiral may have 3 to 6 turns and a height of 10 to 25 mm. The diameter of the spiral may be from 5 to 15 mm. The antenna is mounted on a frame (6) soldered onto a circuit board (3) with a tuning capacitor (4), a light sensor (7) and a battery (5).