GB2467315A

GB2467315A - Set-top box that uses the pre-set stations on an analogue CRT television

Info

Publication number: GB2467315A
Application number: GB0901388A
Authority: GB
Inventors: Martyn Wyatt
Original assignee: Cabot Communications Ltd
Current assignee: Cabot Communications Ltd
Priority date: 2009-01-28
Filing date: 2009-01-28
Publication date: 2010-08-04
Anticipated expiration: 2029-01-28
Also published as: GB0901388D0; GB2467315B

Abstract

The set-top box (STB) 200 includes a station receiver 210 for receiving signals from an external source such as UHF, cable, satellite, network etc., a tuner 220, an RF modulator 240 and a transmitter 250 for connecting to the television set, which enables the set-top box to receive channel signals from an external source and to modulate and send those channel signals to the television. The set-top box additionally includes a received signal synchronisation separator 260, an aerial 280 for detecting the sync signals transmitted by the television tube, a sync separator 290 for the tube sync signals and a comparator 270, which enables the set-top box to compare the sync signals it receives for a particular channel from an external source with the sync signals present in channel that the analogue television is tuned to. By means of these components the set-top box is able to identify the channel corresponding to the channel preset on the television, to select the correct channel from the received signals and to modulate the digital signal onto the correct analogue channel. This enables a user to continue to use their analogue television and its remote controller as normal when the signals are received via the set-top box.

Description

SET-TOP BOX

Field of the invention

The present invention relates to a set-top box and equivalent apparatus adapted to receive a plurality of individually selectable signals and adapted for operation with an analogue television. The present invention additionally relates to a method for providing content from a set-top box to an analogue television.

Background to the invention

When used herein, reference to a set-top box encompasses reference to any device that is adapted to supply to a television or other means for communicating audible I visual content a signal selected from a plurality of signals available from an external source. The external source may be any source including those in the following non-limiting list: a satellite dish; an Ethernet cable; a coaxial cable; a fibre-optic cable; a telephone line (including DSL connections); and broadband over power line. Content, in this context, could mean any or all of video, audio, Internet web pages, interactive games, and other possibilities.

Figure 1 illustrates a typical analogue television 100. Typically, such an analogue television comprises a tuner 101 connected to an antenna capable of receiving high frequency signals supplied in a plurality of frequency bands. In this document reference to a station is intended as reference to a high frequency signal in the form of a content stream provided by a content provider, for example BBC 1. The tuner 101 is adjustable to enable selection of a station and hence a specific high frequency signal to be received by the antenna. An analogue television usually has a number of pre-set channels in association with each of which is stored a respective tuning frequency for a station.

The selected high frequency signal is mixed with a signal generated by an internal oscillator 102 of the television 100 to produce an intermediate signal at a predetermined frequency that is used in further processing of the intermediate signal. An amplifier 103 is used to amplify the intermediate signal and the output from the amplifier 103 is supplied to a demodulator 104. If the particular high frequency signal to which the antenna is tuned corresponds to a channel or station upon which a multi-media content stream is broadcast (for example a combined video and audio signal) the demodulator 104 separates the composite video signal and the audio signal for further processing. A filter for filtering out noise from the video and audio signals is also usually provided.

The audio signal output from the demodulator 104 is supplied to a Frequency Modulation (FM) demodulator 105 where the audio signal is converted from an FM signal to an audio speaker signal and is then amplified (106) before being fed to a speaker.

A composite video signal comprises three components: a video signal which contains the luminance and chrominance information; a horizontal synchronisation signal comprising a series of short pulses indicating the start of each new raster line; and a vertical synchronisation signal comprising a series of much longer pulses indicating the start of a new field. The composite video signal output from the demodulator 104 is connected to a synchronisation separator 108 which extracts the vertical synchronisation signal and the horizontal synchronisation signal from the composite video signal. The vertical synchronisation signal is fed to a vertical time-base circuit 109 which comprises circuitry to convert the vertical synchronisation signal to a saw-tooth vertical hold signal. Similarly, the horizontal synchronisation signal is fed to a horizontal time-base circuit 110 which comprises circuitry to convert the received horizontal synchronisation signal to a saw-tooth horizontal hold signal. The vertical and horizontal hold signals are used to control the scanning movement of the electron beam in a conventional CRT tube. With non-CRT tubes, the vertical and horizontal synchronisation signals continue to be used to control the generation of images on the television or other display monitor.

When a conventional set-top box is used in conjunction with a television, the set-top box modulates whichever station it is tuned to with a fixed modulating frequency to make the station compatible with the analogue television, and supplies the modulated station to the analogue television. Typically, only one

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channel of the television is tuned to the modulating frequency used by the set-top box, irrespective of the station supplied by the set-top box. This means that in order to watch a particular station received by the set-top box, a user must both select the channel of the television which is tuned to the set-top box and also select the correct station on the set-top box which will involve the use of two wholly separate channel selection devices. To many users this is a difficult and confusing procedure. Therefore, it has been an aim in the industry to simplify the connectivity between set-top boxes and televisions.

One approach takes advantage of the fact that the frequency of the television tuner is transmitted a short distance. In US2004/0098739 a digital tuner I decoder for use with an analogue television is described. The digital tuner I decoder picks up signals from the tuner of the analogue television when a channel has been requested on the television and identifies the frequency of the signals it has picked up. The set-top box has a mapping of those digital stations which correspond to existing analogue stations with respect to television tuning frequency and so when a frequency is detected the corresponding digital station is recovered by the set-top box, converted to a compatible television signal, and supplied to the television.

The method described in US200410098739 is costly to implement as it calls for directly determining the frequency of the tuner by counting the frequency of the detected signal. In addition, the accuracy of a frequency counter is strongly dependent on the stability of its time-base. In order to achieve the accuracy necessary to monitor the frequencies of the tuner, the circuits used to generate timing information usually comprise a quartz crystal oscillator within a sealed temperature-controlled chamber known as a crystal oven or OCXO (oven controlled crystal oscillator). Alternatively, an external frequency reference tied to a very high stability oscillator such as a GPS disciplined rubidium oscillator may be used. These types of circuits are expensive.

Summary of the invention

The present invention seeks to provide a system and method which enables a set-top box to be adapted for use with an analogue television without the need for separate channel controls for both the set-top box and the television and which avoids the use of the expensive circuitry of the prior art.

The present invention therefore provides apparatus for supplying a signal to an analogue television from a first external source, the signal including a synchronisation signal, the apparatus comprising: a tuner adapted to select a signal from a plurality of signals provided by the first external source; a modulator for modulating a signal selected by the tuner using a modulating frequency; and a transmitter for transmitting the modulated signal to the analogue television, the apparatus being characterised by a receiver adapted to receive synchronisation information transmitted by the analogue television; a comparator for comparing the synchronisation information transmitted by the analogue television with the synchronisation information in the selected signal; and a controller for controlling selection of the signal to be supplied to the analogue television on the basis of the synchronisation information comparison.

Preferably the apparatus further comprises a synchronisation separator adapted to extract synchronisation information from the selected signal and to communicate the extracted synchronisation information to the comparator. Also the comparator may comprise a phase detector adapted to compare the phase of the synchronisation information extracted from the selected signal with the phase of the synchronisation information transmitted by the analogue television.

Ideally, the synchronisation information transmitted by the analogue television is a horizontal hold signal and the apparatus further comprises a signal processor to convert the horizontal hold signal received by the receiver into a horizontal synchronisation signal.

The apparatus may also include a data store adapted to store information associating selectable signals provided by the first external source with respective modulating frequencies wherein said controller is in communication with the data store.

Ideally, the modulator includes a frequency controller for selecting in dependence upon the synchronisation information comparison one or more frequencies for modulating the selected signal.

In a preferred embodiment the apparatus may include a signal splitter, the signal splitter being adapted to split a signal input to the apparatus and being in communication with the transmitter, whereby the splitter enables a signal input to the apparatus from a source other than the first external source to be transmitted to an analogue television without modulation.

In an alternative aspect the present invention provides a method of associating one or more selectable signals from a plurality of selectable signals with a respective one or more selectable analogue television channels, the method comprising transmitting a modulated signal containing synchronisation information to an analogue television tuned to a first selectable television channel; receiving synchronisation information transmitted by the analogue television; comparing the received synchronisation information with the synchronisation information contained in the modulated signal; in dependence upon the outcome of the comparison either: i) altering the frequency of modulation of the signal and repeating the comparison, or ii) recording the modulation frequency of the modulated signal in association with one of the plurality of selectable signals.

The method preferably further comprises the step of repeating the method in respect of second and further selectable television channels.

Ideally, the step of comparing comprises comparing the phase of the received synchronisation information with the phase of the synchronisation information contained in the modulated signal and the step of receiving synchronisation information may comprise converting a horizontal hold signal transmitted by the analogue television into a horizontal synchronisation signal.

Also, the method may further comprise determining whether comparisons have been performed in relation to signals modulated at all possible modulating frequencies.

Ideally, the step of recording the modulation frequency in association with a selectable signal includes noting a user selection of the signal to be associated with the modulation frequency.

In a further aspect the present invention provides a method for selecting and communicating to an analogue television a signal from a first source comprising a plurality of selectable signals, said method comprising: transmitting a modulated signal containing synchronisation information to an analogue television tuned to a first television channel; receiving synchronisation information transmitted by the television; comparing the received synchronisation information with the synchronisation information contained in the modulated signal; in dependence upon the outcome of the comparison either: iii) altering the frequency of modulation of the signal and repeating the comparison, or iv) identifying a selectable signal associated with the modulation frequency of the modulated signal and transmitting to the analogue television the selectable signal modulated using the modulation frequency.

Preferably, the method further comprises the step of detecting when the television channel to which the analogue television is tuned is changed and repeating the comparison to identify a new selectable signal to be transmitted to the television.

Moreover, the step of comparing may comprise comparing the phase of the received synchronisation signal with the phase of the synchronisation information contained in the modulated signal. Also the step of receiving synchronisation information may include the step of converting a received horizontal hold signal into a horizontal synchronisation signal.

In a preferred embodiment the step of identifying a selectable signal associated with the modulation frequency includes retrieving information stored in a data store in which selectable signals are associated with respective modulation frequencies.

With the present invention a very simple method is provided for enabling set-top box channels to be directly associated with television channels so that users are able, once the learning mode is complete, to select channels using only their television channel control. Also, performance of the method both in the learning mode and the normal channel selection mode of operation is simple and convenient and minimal manufacturing costs through the use of standard components such as a phase detector, rather than a frequency counter is achieved.

Brief Description of the Drawings

Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a block diagram illustrating the components of a conventional analogue television; Figure 2 is a block diagram illustrating the functional components of a set-top box in accordance with the present invention; Figure 3 illustrates the connection of various signal sources with an analogue CR1 television; Figure 4 is a flow chart illustrating the steps in a method for initialising the set-top box of Figure 2.

Detailed Description of the Preferred Embodiments

In Figure 2 the functional components are illustrated of a set-top box 200 adapted for use with an analogue CR1 television. Some of the functional elements of the set-top box are conventional and a detailed description of such conventional elements is omitted as they are considered to be common general knowledge. The set-top box 200 has a station receiver 210 for receiving signals from an external source. The source of the signals may be, amongst others, an Ethernet cable, an fibre optic cable, a satellite dish, a coaxial cable, a telephone line (including DSL connections), Broadband over Power Line, or even an ordinary Very High Frequency (VHF) or Ultra High Frequency (UHF) Radio Frequency (RF) antenna.

The station receiver 210 is connected to a set-top tuner 220 that is adapted to tune the receiver 210 to select a particular station from a plurality of selectable stations supplied by the external source. The selected station passes from the receiver 210, through a signal splitter 211, to the set-top tuner 220 which outputs the selected station, which in this case will be a composite video signal and audio signal, to an RF modulator 240. The RF modulator 240 comprises circuitry to modulate the output from the tuner 220 with an RF frequency signal compatible with analogue television circuitry. The RF modulated signal is then supplied, via a combiner 212 (the function of which is described in greater detail below), to a transmitter 250 adapted for communication with an analogue television. The transmitter 250 may transmit the modulated station wirelessly or by means of a connector such as coaxial cable, to the analogue television.

Control circuitry 230, which is described below in more detail, includes a station selector 231 and frequency controller 232. The station selector 231 is connected to the set-top tuner 220 and comprises circuitry adapted to identify the station to be selected by the set-top tuner 220. The frequency controller 232 comprises circuitry adapted to supply the RF modulator 240 with the appropriate RF frequency for modulating the selected station to make it television compatible.

The output of the set-top tuner 220 is also in communication with a synchronisation separator 260 which comprises circuitry to isolate the horizontal synchronisation signal from the station. Although the description below is specific to the use of the horizontal synchronisation signal it is possible in the alternative to isolate and use the vertical synchronisation signal. The horizontal synchronisation signal is referred to hereafter as the set-top horizontal synchronisation signal and is the same horizontal synchronisation signal which is transmitted as part of the modulated station by the transmitter 250. The output of the synchronisation separator 260 is connected to a first input of a comparator 270 which is described in greater detail below.

The set-top box 200 also includes a scanning RF aerial 280 the function of which is to detect the conventional saw-tooth horizontal hold signal of an analogue CRT television, as described earlier. As the horizontal hold signal is only weakly transmitted by the television, the scanning RF aerial 280 is required to be positioned close to the analogue television. Where the aerial 280 is provided within the set-top box then, similarly, the set-top box must be positioned close to the analogue television. The scanning RF aerial 280 is connected to signal processing circuitry 290 that converts the saw-tooth horizontal hold signal received by the aerial 280 back to the horizontal synchronisation signal which the television used to generate the horizontal hold signal. Preferably, the signal processing circuitry 290 comprises a notch filter. In turn, the output of the signal processing circuitry 290 is connected to a second input of the comparator 270.

The comparator 270 is provided with circuitry which compares the television horizontal synchronisation signal (based on the horizontal hold signal) with the set-top horizontal synchronisation signal and which outputs the result of the comparison to an input of the control circuitry 230. Preferably, the comparator 270 comprises a phase detector which compares the phase of the television horizontal synchronisation signal with the phase of the set-top horizontal synchronisation signal and may comprise one or more of the following non-limiting list of components: an exclusive-OR (XOR) logic gate; an analogue multiplier; a sample and hold circuit; a charge pump; or a logic circuit consisting of flip-flops. The phase detector may be a frequency mixer or analogue multiplier circuit that generates a voltage signal which represents the difference in phase between the two inputs. Thus, the phase detector may be a type I detector (which is a phase detector designed to be driven by analogue signals or square-wave digital signals and produces an output pulse at the difference frequency) in which case the detector always produces an output waveform. Alternatively, the phase detector may be a type II (which is a phase detector sensitive only to the relative timing of the edges of the input pulses) in which case the detector produces a constant output proportional to phase difference when both signals are at the same frequency.

The control circuitry 230 comprises a user input I output (I/O) interface 233 connected to a central control unit 234. A user is able to select the mode of operation of the set-top box using the user I/O interface 233 and the central control unit 234 employs the user I/O interface 233 to indicate to a user at least the current mode of operation of the set-top box 200. Additionally, the control unit 234 may be separately connected to an infra-red signal generator 238 for providing automated remote control of other RF sources, such as a SkyTM box, connected to the receiver 210.

The central control unit 234 may be implemented using dedicated hardware or, as illustrated in Figure 2, using a general purpose central processing unit (CPU) 235 and a program memory unit 236. The program memory 236 is adapted to store instructions which cause the set-top box to function as described below in more detail. In particular, the central control unit 234 controls the operation of the station selector 231 and the operation of the frequency controller 232. The central control unit 234 also has access to a station and frequency store 237. The station and frequency store 237 comprises a data store in which information identifying at least one station is stored in association with an RF modulation frequency.

As illustrated in Figure 3, alternative signal sources may be connected to the television 340 via the set-top box 200. Such alternative signal sources include but are not limited to hard disk storage, a video cassette recorder (VCR) 310, a digital versatile disk (DVD) player, a game machine, a video camera, a close-circuit camera 320 and the like. In this case, the signal input to the set-top box 200 is fed via the splitter 211 directly to the combiner 212 and from there to the television 340.

The instructions stored in the program memory 236 include instructions for two modes of operation: namely a learn mode and a select mode. The learn mode is used to populate the station and frequency store 237, whereas the select mode is used solely for the purpose of identifying and transmitting a selected station from the set-top box to the television.

Figure 4 is a flow chart illustrating the method steps performed by the set-top box during the learn mode (which assumes the set-top box has already detected all available digital channels and that the television is not connected to an analogue aerial. During the learn mode the user selects on the television an analogue television channel which is tuned to receive in analogue form the same station (e.g. BBCI) as the station to which the set-top box is tuned. In step 401 the central control unit 234 monitors the user I/O interface 233 to detect selection of the learn mode. When the user I/O interface 233 receives a user selection of the learn mode in step 402 the central control unit 234 instructs the frequency controller 232 to select a first RF modulating frequency from a range of RF modulating frequencies corresponding to the range of tuning frequencies of the analogue television. In the United Kingdom, the relevant frequency range is 474 MHz -850 MHz covering channels 21 to 68 with an 8 MHz separation between individual channels.

The station received by the set-top box is modulated by the modulator 240 using the RF modulating frequency selected by the frequency controller 232 and this is transmitted to the television via the transmitter 250. The set-top horizontal synchronisation signal is extracted by the separator 260 and supplied to the comparator 270. At the same time, the scanning RF aerial 280 detects the television horizontal hold signal which is converted to a television horizontal synchronisation signal and fed to the comparator 270.

The method then proceeds to step 403 where the central control unit 234 monitors the output of the comparator 270. The output from the comparator 270 indicates whether the television horizontal synchronisation signal is out of phase with the set-top horizontal synchronisation signal. If the RF modulation frequency applied to the set-top box station matches the television tuning, the horizontal synchronisation signals for both the set-top box and the television will be the same and will be in phase. On the other hand, if the RF modulation frequency is different to the channel to which the television is tuned, then the horizontal synchronisation signals will be different and out of phase.

When the two horizontal synchronisation signals are out of phase, in step 404 the central control unit 234 instructs the frequency controller 232 to increase the RF modulation frequency and the set-top horizontal synchronisation signal at this new RF modulation frequency is compared with the television horizontal synchronisation signal to see whether the signals are now in phase. Additionally, each time the frequency controller 232 raises the RF modulation frequency the central control unit 234 checks at step 405 whether the frequency controller 232 has reached the uppermost available RF modulation frequency i.e. whether all possible RF modulation frequencies have been tested. Once all RF modulation frequencies have been scanned the set-top box exits the learn mode. If there are RF modulation frequencies still to be checked, the method continues with, as mentioned earlier, a comparison of the horizontal synchronisation signals of step 403 at the new RF modulation frequency.

When the comparator 270 indicates that the two horizontal synchronisation signals are in phase for a particular RF modulating frequency, the method proceeds to step 406. At step 406 the central control unit 234 checks the station and frequency store 237 to see whether the RF modulation frequency has already been stored in association with a set-top box channel. If the RF modulating frequency provided by the frequency controller is already stored, the method proceeds to step 404. If the RF modulating frequency is not already stored, at step 407 the RF modulating frequency is stored in the station and frequency store 237 in association with the selected set-top box channel. The central control unit 234 may include the option of overwriting a previously stored RF modulating frequency.

The same procedure may then be repeated for other television channels in each case the RF modulating frequency being matched to the tuning of the that television channel by means of the horizontal synchronisation signals and the matching RF modulating frequency then being associated in the station and frequency store 237 with a user selected set-top box channel. In this way the station and frequency store 237 can build up a record of the frequencies of the pre-set channels that the analogue television is using (as the frequencies correspond to the RF modulating frequencies of the set-top box) and for each of these television channel frequencies a set-top box station is mapped to the television channel frequency.

In a similar manner if the learn mode is selected when the set-top box 200 is tuned to a separate external RF source 330, the RF modulating frequency is stored in association with identification of the tuning for the external RF source.

Moreover, in such circumstances the station and frequency store 237 may additionally include IR control data for instructing, using IR communication, correct operation of the separate RF source remotely. When the modulating frequency matches a station in the store 237 which includes IR control data, the IR control data is read by the central control unit 234 and the control data is transmitted to the RF source by means of the IR signal generator 238. The IR control data may be as simple as a command to activate the RF source from standby or may consist of instructions enabling individual channels on the separate RF source to be selected.

During the normal mode of operation, the output of the comparator 270 is monitored either continuously or at regular intervals. When the television and the set-top box are first turned on the central control unit 234 instructs the frequency controller 232 to check across the range of RF modulating frequencies to find the RF modulating frequency which results in the horizontal synchronisation signals being in phase. When the comparator 270 determines that the synchronisation signals are in phase, the RF modulating frequency is checked against the contents of the station and frequency store 237 to identify whether there is a set-top box station associated with that RF modulating frequency. If there is an entry in the store 237 for the RF modulating frequency then the station selector 231 is instructed to tune to that associated station. Where no entry appears in the store for the RF modulating frequency, the set-top box remains tuned to its current station.

When a user changes to a different pre-set channel on their television, i.e. tunes away from the current signal, this is detected by the comparator 270. The television horizontal synchronisation signal changes from being in phase to being out of phase with the transmitted horizontal synchronisation signal. When the central control unit 234 is informed by the comparator that the two horizontal synchronisation signals are no longer in phase, the central control unit 234 instructs the frequency controller 232 to vary the RF modulation frequency until the synchronisation signals are once more back in phase. Once the correct RF modulation frequency has been identified the station and frequency store 237 is checked to identify the correct station associated with that RF modulating frequency and the set-top box is re-tuned to the correct station. The frequency controller 232 may check all possible RF modulating frequencies or, preferably, the frequency controller 232 may check in turn each RF modulating frequency which is already stored in the station and frequency store 237 and then only perform a full check of all possible RF modulating frequencies if none of the existing stored RF modulating frequencies are found to achieve in-phase horizontal synchronisation signals.

It will be apparent that the above apparatus and methods described herein provide significant benefits. These benefits include, but are not limited to: users being able, once the learning mode is complete, to select channels using only their television channel control; greatly simplified operation both in the learning mode and the normal channel selection mode of operation; and minimal manufacturing costs through the use of standard components such as a phase detector, rather than a frequency counter. Of course, additional benefits will be apparent to those skilled in the art.

The above describes preferred implementations of the present invention.

A person of ordinarily skilled in the art will appreciate that there are alternative implementations which do not depart from the scope of the present invention.

The scope of the present disclosure should therefore be taken to encompass any novel feature or combination of features or equivalents thereof, which are disclosed herein, either explicitly or implicitly, or any generalisation thereof.

Claims

Claims 1. Apparatus for supplying a signal to an analogue television from a first external source, the signal including a synchronisation signal, the apparatus comprising: a tuner adapted to select a signal from a plurality of signals provided by the first external source; a modulator for modulating a signal selected by the tuner using a modulating frequency; and a transmitter for transmitting the modulated signal to the analogue television, the apparatus being characterised by a receiver adapted to receive synchronisation information transmitted by the analogue television; a comparator for comparing the synchronisation information transmitted by the analogue television with the synchronisation information in the selected signal; and a controller for controlling selection of the signal to be supplied to the analogue television on the basis of the synchronisation information comparison.
2. Apparatus according to claim 1, further comprising a synchronisation separator adapted to extract synchronisation information from the selected signal and to communicate the extracted synchronisation information to the comparator.
3. The apparatus according to claim 2, wherein the comparator comprises a phase detector adapted to compare the phase of the synchronisation information extracted from the selected signal with the phase of the synchronisation information transmitted by the analogue television.
4. The apparatus according to any one of the preceding claims, wherein the synchronisation information transmitted by the analogue television is a horizontal hold signal and the apparatus further comprises a signal processor to convert the horizontal hold signal received by the receiver into a horizontal synchronisation signal.
5. The apparatus according to any one of the preceding claims, further comprising a data store adapted to store information associating selectable signals provided by the first external source with respective modulating frequencies wherein said controller is in communication with the data store.
6. The apparatus according to any one of the preceding claims, wherein the modulator includes a frequency controller for selecting in dependence upon the synchronisation information comparison one or more frequencies for modulating the selected signal.
7. The apparatus according to any one of the preceding claims, further comprising a signal splitter, the signal splitter being adapted to split a signal input to the apparatus and being in communication with the transmitter, whereby the splitter enables a signal input to the apparatus from a source other than the first external source to be transmitted to an analogue television without modulation by the apparatus.
8. The apparatus according to claims 5 and 7, further comprising an IR signal generator for issuing IR signals to a second external source wherein IR control.data for the second source is stored in the data store in association with the modulating frequency associated with the second source.
9. A method of associating one or more selectable signals from a plurality of selectable signals with a respective one or more selectable analogue television channels, the method comprising transmitting a modulated signal containing synchronisation information to an analogue television tuned to a first selectable television channel; receiving synchronisation information transmitted by the analogue television; comparing the received synchronisation information with the synchronisation information contained in the modulated signal; in dependence upon the outcome of the comparison either: i) altering the frequency of modulation of the signal and repeating the comparison, or ii) recording the modulation frequency of the modulated signal in association with one of the plurality of selectable signals.
10. The method according to claim 9, further comprising the step of repeating the method in respect of second and further selectable television channels.
11. The method according to either of claims 9 or 10, wherein the step of comparing comprises comparing the phase of the received synchronisation information with the phase of the synchronisation information contained in the modulated signal.
12. The method according to any one of claims 9 to 11, wherein the step of receiving synchronisation information comprises converting a horizontal hold signal transmitted by the analogue television into a horizontal synchronisation signal.
13. The method according to any one of claims 9 to 12, further comprising determining whether comparisons have been performed in relation to signals modulated at all possible modulating frequencies.
14. The method according to any one of claims 9 to 13, wherein the step of recording the modulation frequency in association with a selectable signal includes noting a user selection of the signal to be associated with the modulation frequency.
15. The method according to any one of claims 9 to 14, wherein the step of recording the modulation frequency in association with a selectable signal includes recording the modulation frequency and IR control data in association with a user selection of a separate further signal source.
16. A method for selecting and communicating to an analogue television a signal from a first source comprising a plurality of selectable signals, said method comprising: transmitting a modulated signal containing synchronisation information to an analogue television tuned to a first television channel; receiving synchronisation information transmitted by the television; comparing the received synchronisation information with the synchronisation information contained in the modulated signal; in dependence upon the outcome of the comparison either: iii) altering the frequency of modulation of the signal and repeating the comparison, or iv) identifying a selectable signal associated with the modulation frequency of the modulated signal and transmitting to the analogue television the selectable signal modulated using the modulation frequency.
17. The method according to claim 16, further comprising the step of detecting when the television channel to which the analogue television is tuned is changed and repeating the comparison to identify a new selectable signal to be transmitted to the television.
18. The method according to either of claims 16 or 17, wherein the step of comparing comprises comparing the phase of the received synchronisation signal with the phase of the synchronisation information contained in the modulated signal.
19. The method of any one of claims 16 to 18, wherein the step of receiving synchronisation information includes the step of converting a received horizontal hold signal into a horizontal synchronisation signal.
20. The method according to any one of claims 16 to 19, wherein the step of identifying a selectable signal associated with the modulation frequency includes retrieving information stored in a data store in which selectable signals are associated with respective modulation frequencies.
21. The method according to claim 20, wherein the step of retrieving information in the data store includes retrieving information on the modulating frequency associated with a second source, the information including infra-red control data for controlling operation of the second source.
22. Apparatus substantially as hereinbefore described with reference to Figure 2 and Figure 3.
23. A method for recording information identifying a frequency in a set-top box substantially as hereinbefore described with reference to Figure 4.
24. A method for selecting and transmitting to an analogue television a signal from a source comprising a plurality of selectable sources substantially as hereinbefore described with reference to Figures 2 to 4.