GB1389228A - Apparatus for deriving sound signals from television receivers - Google Patents

Abstract

1389228 Radio receivers A J BURTON 7 March 1972 [28 Sept 1971] 45105/71 Heading H3Q Apparatus for deriving a high fidelity sound signal from a television receiver, comprises pick-up means to be placed in or near the television receiver and arranged to pick-up a signal from stray radiation, frequency modulated by audio information, emitted by the receiver, the pick having maximum sensitivity to electromagnetic or electrostatic fields at a frequency substantially equal to the difference between sound and vision carriers, means for amplifying the signal picked-up and applying them to a frequency discriminator. Coil L1, Fig. 2, which may be provided with a ferrite core 21 picks up the intercarrier sound modulated signal from the vicinity of the video detector, it is amplified in tuned amplifier 18, limited by limiter 19 and demodulated in discriminator 20. The coil may be tuned by means of a capacitor and connected to the amplifier by way of a balanced and screened transmission line coupled to the amplifier by means of a transformer (Fig. 4, not shown). The transformer T2, Fig. 5, may be centre-tapped, the tap being connected to the screening which is earthed via a capacitor C2. The signal may alternatively be picked-up by means of a dipole aerial (Fig. 3, not shown), which may be coupled to the amplifier via a screened and balanced transmission line and isolating transformer (Fig. 6, not shown).