GB2166278A

GB2166278A - Sound recording interface for a domestic video cassette recorder

Info

Publication number: GB2166278A
Application number: GB08426805A
Authority: GB
Inventors: Peter John Court Marlow
Original assignee: Individual
Current assignee: Individual
Priority date: 1984-10-23
Filing date: 1984-10-23
Publication date: 1986-04-30
Also published as: GB8426805D0

Abstract

A sound recording interface for a domestic video cassette recorder which creates a standard television signal on a spare UHF channel of a 'black' picture and the desired sound. This signal can be recorded and played back by the video cassette recorder like any other television signal. The interface is connected to the video cassette recorder via the UHF aerial feed in such a way as not to interfere with broadcast television signals or radiate unwanted signals. Radio programs can therefore be recorded on a video cassette recorder taking advantage of the long length of video tape (as compared with audio cassette) and the sophisticated timer on the recorder. Any mix of radio and television programs can be recorded. Reference is made to the provision by the video signal generator of a "non-black" picture, and moving colour display changing according to level or frequency of audio input. <IMAGE>

Description

SPECIFICATION Sound recording interface for a domestic video cassette recorder This invention relates to a sound recording interface for a domestic video cassette recorder (refered to as a VCR).

A VCR allows the recording of broadcast television programs. Recordings may be played back through a standard domestic television receiver.

The VCR is operated either manually or by a preset timer. The timer is usually very sophisticated, being able to control precise on-off times for several different broadcasts on different channels.

Currently available VCRs do not allow audio or sound only or radio broadcasts to be recorded under timer control. However, this function would be very useful for three reasons. Firstly, the length of audio tapes is restricted to one hour per side whereas video tapes can be up to four hours long.

Therefore longer radio programs such as plays or concerts could be recorded completely under timer control. Secondly, the sophisticated timer allows multiple recordings as described above. These timers are not commercially available by themselves for incorporation into a radio/recorder system.

Thirdly, the recording of all broadcast programs, whether radio or television, can be centralised on to one recording machine.

According to the present invention the sound recording interface allows an audio signal, such as a radio broadcast, to be recorded on video tape by the VCR under timer or manual control. The sound signal is recorded in the same way that television sound is recorded. However the interface generates a "black" television picture which is recorded in place of the usual broadcast television picture.

When the video tape is played back in the usual way the audio will come through the sound channel of the television receiver, while a black picture will be displayed.

The interface is connected to the VCR in series with the UHF aerial feed. A "black" vision signal is generated internally. This is fed, with the audio signal, into a modulator. This produces a TV signal on a spare UHF television channel. This signal is mixed into the aerial feed. The aerial input is buffered to avoid the radiation of any generated TV signal. The mixed aerial signal is fed to the VCR.

The VCR is able to tune into the usual broadcast TV channels and the TV signal with the audio. The latter is assigned to a spare channel. Any mix of radio or TV programs can be recorded.

A specific embodiment of the invention will be described by way of example with reference to the accompanying drawing in which: Figure 1 shows a block diagram of the sound recording interface.

Figure 2 shows the circuit of the video generator, modulator and aerial buffer.

Refering to the drawing the interface comprises five blocks (Figure 1). The first block is the power supply. This takes standard AC 50 hertz mains and converts it by conventional linear means to 15 volts DC at 200 milliamps. A standard linear regulator produces a + 5 volt line from the 15 volt supply.

The second block is the audio amplifier. This is a conventional linear amplifier circuit built around the commercially available integrated circuit the LM748 made by National Semiconductors. The input is a standard DIN audio interface with the left and right channels of a stereo signal being mixed to form a mono signal - the interface only records in mono. Circuit gain is adjustable from 0.15 to 1.6 to cope with inputs from different sources. The output is 0.5 volts peak to peak.

The third, fourth and fifth blocks are shown on Figure 2.

The third block is the video signal generator. It uses a commercially available VDU chip (IC1) type EF9364A made by Thomson-CSF to produce synchronising pulses. These are buffered, inverted and attenuated to 0.1 volts peak to peak by a transistor stage (transistor 4) for insertion into the video modulator (M1). The circuit around IC1 and transistor 4 is standard.

The fourth block is the video modulator. This is a commercially available unit type UM1287 from Astec International (Reading, UK). On the drawing it is designated as Ml. The configuration is standard.

The unit produces a UHF British standard television signal, with sound, with 0.1 volts of input synchronising pulses and 0.5 volts of audio. The unit is tunable by adjusting internal cores and variable resistor 8.

The fifth block is the aerial buffer and mixer. The UHF aerial is fed into a standard 12 dB attenuator made up with resistors 14, 15 and 16. It then is amplified about 24 dB by amplifier integrated circuit type OM335 (IC2), commercially available from Mullard Ltd. The output is fed into a standard star mixer made up with resistors 9, 10 and 11. The mixer output is fed out through a coaxial cable to the VCR. Capacitor 12 prevents amplifier feedback oscillation. The UHF aerial is buffered in this way to prevent any of the modulator output being radiated via the aerial. The back attenuation of the circuit IC2 and resistors 14, 15 and 16 is about 50 dB.

A number of modifications will now be evident within the scope of the invention. Each of the five blocks could be implemented using different components to those described above, provided that the overall effect was the same. The unit could be "stand-alone" or built into another piece of equipment such as an audio tuner. It would not then need a separate power supply. The unit could be used without the UHF aerial by connecting the modulator (M1) output directly into the VCR. IC2 would be unnecessary.

Also, block 3, the video signal generator, could be modified to provide a "non-black" picture. IC1 could have additional conventional components added to provide different displays. These could be a fixed or varying message in monochrome or colour, or a moving colour display changing accordrig to the level or frequency of the audio input.

Cost prevents any of these modifications now, but as integrated circuit prices fall this may change.

Claims

1. A sound recording interface for a domestic video cassette recorder which creates a standard television signal on a spare UHF channel of a "black" picture and the desired sound. This signal can be recorded and played back by the video cassette recorder like any other television signal. The interface feeds the "sound" television signal through the UHF aerial input to the video cassette recorder without interfering with broadcast television signals or radiating externally. The interface is "stand-alone" receiving an audio input from an external source.

2. A sound recording interface for a domestic video cassette recorder as claim 1 not "standalone" but built into another piece of equipment such as an audio tuner.

3. A sound recording interface for a domestic video cassette recorder as claim 1 but without an external UHF aerial being attached. The video recorder would not be able to record broadcast television programs at the same time that the interface was attached.

4. A sound recording interface for a domestic video cassette recorder as claim 1 but with a "nonblack" television picture consisting of a fixed or changing monochrome or coloured message.

5. A sound recording interface for a domestic video cassette recorder as claim 1 but with a moving colour display, varying according to the level or frequency of the audio input, instead of a "black" picture.

6. An interface as described by claims 1 to 5 inclusive for use without the video cassette recorder.