Patent GB-1197502-A (GB)
Title: Improvements in or Relating to Video Recorder System
IPC: H04N5/91
Filed: 1967-08-11
Abstract: 1,197,502. Magnetic tape recording. WINSTON RESEARCH CORP. 11 Aug., 1967 [27 Oct., 1966], No. 37096/67. Heading-G5R. A video-tape record-playback system in combination with the circuitry of conventional television receiver tunable to established broadcast channels and capable of generating a video signal comprises: a tape transport; transducer means for recording and playing back a video signal biased at a subharmonic of the video carrier frequency of one of the established channels; biasing means coupled to the transducer means for biasing as above specified; an input terminal for receiving a conventional television video signal; means coupling the input terminal to the transducer means for recording; and a transducer output terminal coupled to an input of the tuner of the television receiver for playback of a signal at the video carrier frequency. Video-recording.-As shown, video signals from an output (e.g. the grid of the cathode ray tube) of a conventional television receiver 13 are passed through a current driver 14 (to convert the voltage output signal to a current input signal) to a record-playback video head 12. In the position shown of a switch 15, the signals pass via a lead 42 to a non-magnetic conductive gap spacer 41, which may take the form of a strip of copper, titanium or the like. With switch 15 in its lower position the signals pass to head 12 through its core winding 40. The video bias supply 16 is of a conventional type controlled by a power regulator, but its frequency must be a subharmonic (preferably one half or one-third) of the carrier frequency of one of the established television channels. The bias signal is passed to the conductive gap spacer 41 via timed transformer 44, terminal 43 and lead 42. Video playback.-Power switch 16A on the bias supply is set for playback and switch 15 is opened. The output signal, from core winding 40, is conducted to a terminal 17. Terminal 17 is connected through a matching network 20 either directly, or as described below, to the tuner 18 of TV receiver 13. Matching network 20 may be a transformer with a turns ratio chosen to match the impedance of the recording head (about 20 ohms), to the impedance of the TV receiver ( about 300 ohms). The alternative connection to tuner 18 is, as shown, via a conventional two-signal coupler 21, so that the receiver may be used for receiving broadcast television signals as well as played-back signals. Audio recording.-The audio signal, e.g. from the speaker terminals of TV receiver 13, is passed through audio record driver 25 and switch 27 (closed at this stage) to an audio head 24. (Alternatively, head 24 may be replaced by an additional gap in the video head 12). An audio bias supply 26 is connected to the left of switch 27. Audio playback.-Switch 27 is opened, and the audio signal is received at a terminal 28. Terminal 28 is connected through an amplifier 29 (to bring the signal up to an " easy listening " level) to the audio input (conventionally, the speaker terminals) of TV receiver 13. In a modification of the playback arrangement (Fig. 2, not shown), the audio signal is fed through the coupler 21 to the tuner 18. For this purpose the audio signal from terminal 28 is passed through a conventional amplifier and then through a frequency-modulation oscillator to develop a frequency-modulated signal of a frequency (e.g. 4.5 MHz) normally used for audio transmission in conventional TV broadcasting. This FM signal is applied to one of the inputs of a non-linear mixer (e.g. a conventional mixer diode); the other input is connected to the video bias supply. The output of the mixer is connected (optionally through an attenuating resistor or pad) through the coupler 21 to the tuner 18. Preferably (as shown), the video head 12 is of the kind disclosed in Specification 1,159,987. Reference has been directed by the Comptroller to Specification 1,106,784.