GB2214741A

GB2214741A - Video tape recorder/player devices

Info

Publication number: GB2214741A
Application number: GB8809088A
Authority: GB
Inventors: Thomas Baxter
Original assignee: Philips Electronic and Associated Industries Ltd
Current assignee: Philips Electronics UK Ltd
Priority date: 1988-01-22
Filing date: 1988-04-18
Publication date: 1989-09-06
Also published as: GB8809088D0; GB8801442D0; KR0142101B1; KR890012297A

Abstract

A video tape record/player device is adapted to select a playback channel to be any one of a plurality of UHF television channels. A microcontroller in the device sets the UHF tuner in the device to each UHF channel in turn and tests the signal level in the channel. A free channel containing substantially no interference signals is selected, when found, as the playback channel. Once a selection is made, the microcontroller sets the playback channel frequency to that of the selected channel. <IMAGE>

Description

DESCRIPTION: VIDEO TAPE RECORDER/PLAYER DEVICES This invention relates to video tape players which are operable to produce video/audio signals from information recorded on a tape and which are further operable to modulate a carrier signal with these video/audio signals for transporting them to a television receiver in an information channel which is provided in a suitable transmission medium, the information channel having a given bandwidth with respect to the frequency of the carrier signal.

The information channel is commonly known as a "playback channel" and will be so termed hereinafter.

For domestic use such a video tape player conventionally forms part of a composite video tape recorder/player device, the recorder part of which is tunable selectively to any one of a plurality of UHF television channels to receive and to record onto tape television transmissions transported in these channels.

The UHF television channel allocation for Western Europe covers 48 channels which are numbered 21 to 68. Details of this channel allocation are given in IBA Technical Review No. 10, May 1978.

The playback channel used for a domestic video tape recorder/player device is notionally a particular one of these 48 UHF television channels which has not been allocated to a terrestrial broadcast television station. However, there is often interference present in the playback channel from a broadcast channel transporting a television transmission, depending on where the device is located. There is a facility on many video tape recorder/player devices for making a manual adjustment to the frequency of the carrier signal which defines the playback channel to move the channel relative to an interfering broadcast channel, but this is not always successfuL in reducing the interference. The interference from broadcast channels has been found to be particularly bad in certain European locations where television transmissions from several different transmitters can be received.

It is an object of the present invention to provide a video tape recorder/player device in which this problem of interference is mitigated.

According to the present invention, a video tape recorder/player device includes test means for determining the signal levels present in UHF television channels to which the device can be tuned, selection means for selecting for use as a playback channel for the device a channel in which the signal level is less than a predetermined value, and means for setting the carrier signal for the playback channel to the frequency defining the selected channel.

By these means, it is highly probable that a playback channel can be selected which is substantially free from interference from any broadcast channel.

In carrying out the invention, the test means may be arranged to determine the signal levels either in the complete range of UHF television channels to which the device can be tuned, or in only those channels which may be notionally "free" for selection as the playback channel in the sense that they are not allocated for use as broadcast channels which serve a territorial location where the device is to be used. In the latter case, the testing would not need to cover such a large range of possible signal Levels because only interference signals levels would be tested for. In the former case, a broadcast channel which is not currently in use could be selected as the playback channel.

The testing of the signal leveLs, and the subsequent selection and setting of the pLayback channel may be carried out only on setting-up of the device at a particular territorial location, in which case it would involve only UHF television channels which are not already allocated for use as broadcast channels which serve that Location. Alternatively, the testing of the signal levels, and the subsequent selection and setting of the playback channel may be carried out periodically, for instance at set time intervals. In this case, it would be possible to change the channel which is being used as the playback channel. Such a change may also be initiated by a viewer when interference occurs in a previously interference-free playback channel.A further alternative is for the testing of the signal levels, and the subsequent selection and setting of a channel as the playback channel, to be carried out each time the playback channel is to be taken into use. Suitable control means would be provided for the control of these various operations.

Of course, a television receiver to which the device is connected would need to be retuned to a new playback channel.

The test means and selection means can be implemented as a microcontroller and associated memory, a channel frequency selector, a tuner including a local oscillator, and a signal level detector, said microcontroller being programmed according to a signal level test and select algorithm which is initiated as required to cause the channel frequency selector to set the tuner to the carrier signal frequency of each of the channels to be tested in turn, said signal level detector being operable to detect the level of the signal in the channel concerned and said microcontroller being responsive in accordance with the signal values as received by it from said signal level detector to allocate one of the tested channels as the playback channel.

The test and select operation under the control of said algorithm may be such that the first channel tested whose signal level does not exceed said predetermined value is selected as the playback channel, following which this operation is terminated.

Alternatively, the signal levels of all the channels to be tested may be determined and their signal values stored in the memory, following which the channel having the lowest signal level is selected as the playback channel. The test and select algorithm may also involve identifying by their signal levels, and excluding from possible selection as the playback channel, those channels which are used as broadcast channels and serve the territorial location where the device is situated.

Advantageously, the microcontroller and associated memory, the channel frequency selector, and the tuner with the local oscillator may be those already provided in a video tape recorder/player device for its normal operation. The only additional means required for the test means and selection means is the signal level detector and additional software for the test and select algorithm.

The setting means for setting the carrier signal for the playback channel to the frequency defining the channel selected as the playback channel may be a digital-to-analogue converter which, under the control of the microcontroller, sets a voltage controlled oscillator that generates the carrier signals for the device to operate at the required frequency, said algorithm including the steps of programming the microcontroller for this control function.

In order that the invention may be more fully understood reference will now be made by way of example to the accompanying drawings,-of which: Figure 1 is a block diagram of a conventional video tape recorder/player device; and Figure 2 is a block diagram of a video tape recorder/player device embodying the invention.

Referring to the drawings, the conventional video tape player/recorder device represented by the block diagram in Figure 1 has an aerial input terminal AE for receiving television signals which are broadcast in UHF television channels. This input terminal AE is connected through a combiner COMB to a video output terminal VD which is for connection to the aerial input terminal of a television receiver TV. The input terminal AE is also connected to the input of a voltage-controLled amplifier VCA the output of which is connected to the input of a tuner TUN with a local oscillator LO. A channel frequency selector CFS is operable to set the tuner TUN to the various UHF television channels under the control of a microcontroller MIC. The output of the tuner TUN is connected to the input of intermediate frequency stages IF.A feedback connection from the intermediate frequency stages IF to the amplifier VCA provides for automatic voltage control of this amplifier by a feedback voltage FV. The output of the intermediate frequency stages IF is connected to the input of a demodulator DEM which retrieves the video baseband signal and an audio signal contained in the received television signal. These signals are then passed to a tape record/play element R/P for storage on a tape.

The video tape player/recorder device also comprises a modulator MOD and a voltage controlled oscillator VCO. The oscillator VCO is preset to produce a carrier signal CS which defines the playback channel for the device. This playback channel is typically one of the UHF television channels 30 to 40 and can be preset within this number range, as signfied by the resistance element RES. On playback from a recorded tape, a composite video baseband signal CVBS and an audio signal AS are applied from the element R/P to the modulator MOD which modulates the carrier signal CS with these signals. The resulting modulated signal is applied to the video output terminal VD via the combiner COMB. The signal CVBS contains the original video baseband signal together with synchronising signals for the television receiver.

The channel selection and the recording playback operations of the element R/P are controlled by the microcontroller MIC in accordance with control signals from a user interface (not shown).

In a video tape player/recorder device embodying the invention as represented by the block diagram in Figure 2, the elements which have counterparts in Figure 1 have been given the same references as their counterparts. The device in Figure 2 additionally comprises an analogue-to-digital converter ATD, a digital-to-analogue converter DTA, which replaces the resistance element RES in the device of Figure 1, and additional software for the microcontroller MIC.

The converter ATD is connected to receive the feedback voltage FV from the intermediate frequency stages IF and converts this voltage into a digital value VDV which is inputted to the microcontroller MIC. Because of the existing automatic voltage control which is provided for over the feedback connection from the stages IF to the amplifier VCA, the magnitude of the feedback voltage FV is an accurate ensure of the level of the received signal in the UHF television channel to which the tuner TUN is currently set.

The converter DTA is operable under the control of the microcontrolLer MIC to set the voltage-controlled oscillator VCO to produce a carrier signal the frequency of which defines as the playback channel any one of the UHF television channels to which the device can be tuned. The converters ATD and DTA may be the integrated circuit type PFC 8591 (Philips) which is controlled by the microcontroller MIC via a two-wire bi-directional I2C bus.

This integrated circuit, together with additional software for the microcontroller MIC, are the only extra means required for the performance of the invention.

In order to select one of the UHF television channels as the playback channel the microcontroller MIC is operable in accordance with a signal level test and select algorithm to apply successive digital channel tuning command signals tcs to the channel frequency selector CFS which is responsive to these command signals to apply to the tuner TUN successive tuning voltages tv which tune the local oscillator LO therein to the carrier frequency for each UHF television channel in turn. As each UHF television channel is tuned into, the feedback voLtage FV is converted by the anaLogue-to-digital converter ATD into the appropriate digital value VDV which is fed into the microcontroller MIC.The digitaL values VDV are used by the microcontroLLer MIC to seLect one of the tested UllF television channels as the playback channeL. A digital command signal its signifying the selected channel is produced by the microcontroller MIC and converted by the digital-to-analogue converter DTA into a tuning voltage ptv which tunes the voltage controlled oscillator VCO to the carrier frequency of the selected channel.

The programming of the micrcontroller MIC in the performance of the invention may be such that the test, selection and setting sequence is carried out only on setting up of the device at a particular territorial location, or it is carried out periodically, or it is carried out each time the playback channel is to be taken into use. The selection of a UHF television channel as the playback channel may involve testing all of the UHF television channels; or may involve testing only those channels which are not being used as broadcast channels which serve a territorial location where the device is to be used.

The first "free" channel that is found may be selected as the playback channel, or all the signal levels of all the channels involved may by determined and a selection made of the most interference-free channel as the playback channel.

Instead of using the feedback voltage FV, the determination of the signal levels in the UHF television channels can involve the actual UHF signals which are received in the respective channels. This would require a signal level detector to which the received UHF signals are applied and which is responsive to produce an analogue voltage representing the UHF signal level.

This analogue voltage would then be digitised in the same manner as the feedback voltage FV for application to the microcontroller MIC.

From reading the present disclosure, other modifications will be apparent to persons skilled in the art. Such modifications may involve other features which are already known per se and which may be used instead of or in addition to features already described herein. Although claims have been formulated in this application to particular combinations of features, it should be understood that the scope of the disclosure of the present application also includes any novel feature or any novel combination of features disclosed herein either explicitly or implicitly or any generalisation thereof, whether or not it relates to the same invention as presently claimed in any claim and whether or not it mitigates any or all of the same technical problems as does the present invention.

The applicants hereby give notice that new claims may be formulated to such features and/or combinations of such features during the prosecution of the present application.

Claims

CLAIMS:

1. A video tape recorder/player device characterised by including test means for determining the signal levels present in UHF television channels to which the device can be tuned, selection means for selecting for use as a playback channel for the device a channel in which the signal level is less than a predetermined value, and means for setting the carrier signal for the playback channel to the frequency defining the selected channel.

2. A video tape recorder/player device as claimed in Claim 1, characterised in that said test means is arranged to determine the signal levels in a range of UHF television channels to which the device can be tuned, before a selection of a channel for use as the playback channel is made.

3. A video tape recorder/player device as claimed in Claim 1, characterised in that said test means is arranged to determine the signal levels only in those channels which are free for selection as the playback channel because they are not being used as broadcast channels which serve a territorial location where the device is to be used, before a selection of a channel for use as the playback channel is made.

4. A video tape recorder/player device as claimed in any one of Claims 1 to 3, characterised in that control means are provided for causing the testing of the signal levels by said test means and the subsequent selection and setting of the playback channel to be carried out only on setting up of the device at a particular territorial location.

5. A video tape recorder/player device as claimed in any one of Claims 1 to 3, characterised in that control means are provided for causing the testing of the signal levels by said test means and the subsequent selection and setting of the playback channel to be carried out periodically.

6. A video tape recorder/player device as claimed in any one of Claims 1 to 3, characterised in that control means are provided for causing the testing of the signal levels by said test means and the subsequent selection and setting of the playback channel to be carried out each time the playback channel is to be taken into use.

7. A video tape recorder/player device as claimed in any preceding CLaim, characterised in that said test means and selection means are implemented as a microcontroller and associated memory, a channel frequency selector, a tuner including a local oscillator and a signal level detector, said microcontroller being programmed according to a signal level test and select algorithm which is initiated as required to cause the channel frequency selector to set the tuner to the carrier signal frequency of each of the channels to be tested in turn, said signal level detector being operable to detect the level of the signal in the channel concerned and said microcontroller being responsive in accordance with the signal values as received by it from said signal level detector to allocate one of the tested channels as the playback channel.

8. A video tape recorder/player device as claimed in Claim 7, characterised in that the test and select operation of the microcontroller under the control of said alogorithm is such that the first channel tested whose signal level does not exceed said predetermined value is selected as the playback channel, following which this operation is terminated.

9. A video tape recorder/player device as claimed in Claim 7, characterised in that the test and select operation of the microcontroller under the control of said algorithm is such that the signal levels of all the channels to be tested are determined and their signal values stored in the memory, following which the channel having the lowest signal leveL is seLected as the playback channel.

10. A video tape recorder/player device as claimed in Claim 7, Claim 8 or Claim 9, characterised in that the test and select operation of the microcontroller under the control of said algorithm also involves identifying by their signal -levels, and excluding from possible selection as the playback channel, those channels which are used as broadcast channels and serve the territorial location where the device is situated.

11. A video tape recorder/player device as claimed in any one of Claims 7 to 10 characterised in that said microcontroller and associated memory, said channel frequency selector, and said tuner with the local oscillator are those already provided in said device for its normal recording-playback operations.

12. A video tape recorder/player device as claimed in any preceding Claim, characterised in that the setting means for setting the carrier signal for the playback channel to the frequency defining the channel selected as the playback channel, is a digital-to-analogue converter which, under the control of.

the microcontroller, sets a voltage controlled oscillator that generates the carrier signal for the device to operate at the required frequency, said algorithm including the steps for programming the microcontroller for this control function.

13. A video tape recorder/player device, substantially as hereinbefore described with reference to the accompanying drawings.