Wireless Headphones (Transmitter)

0 4 WIRELESS HEADPHONES (TRANSMITTER) A circuit for the transmission, with good quality, of the sound output of a TV re- ceiver over a couple of metres. The input signal for the circuit is taken from the headphone or video recorder output of the TV receiver. If these are not available, NEVER ATTEMPT TO FIT ONE YOURSELF: THE CHASSIS OF THE TV SET MAY BE AT A LETHAL HIGH VOLTAGE. The audio signal is amplified by ICI, which has been given some extra `body" by the addition of an output buffer, Ti. Capacitor C4 has a potential that is equal to half the supply voltage (via R3-R4), on to which the amplified audio signal is superimposed. The resulting varying direct voltage is used as the supply voltage for emit transistor T2 via the primary of L2. The carrier os- cillator, also formed by T2, can oscillate between 1,750 kHz and 3,500 kHz. The consequent amplitude-modulated signal across the secondary of L2 is strong enough to span a few metres. A ferrite rod is used as transmit antenna. D...