Cordless telephone with IR link between handset and fixed station - has variable-frequency oscillator at each end for modulation and level control of respective IR transmitters

摘要

The handset (1) equipped with a loudspeaker (4) and microphone (5) is linked by photodiode (12) and LED (13) to the fixed station (2), at which the FM receiver (14), oscillator (15) and infrared transmitter (16) are coupled to a conventional telephone set (3) with a cradle switch (21). The two modulation oscillators (7,15) operate at different centre frequencies, mixed with the received frequency to produce sum and difference frequencies for demodulation, and variable for selection of well-defined channels. USE/ADVANTAGE - With cordless telephones linked to desk- or wall-mounted stations, esp. low susceptibility to stray radiation favours multichannel and duplex transmission at low component cost.