GB2105150A - Television systems - Google Patents

Abstract

A control unit 2 is connected via a line 3 to a remote unit 4 connected to a video source such as a television camera 1. To reduce cable requirements, the control unit 2 supplies mixed sync and (in a colour system) burst to the line whilst the remote unit supplies non-composite video from the camera to the other end of the same line so that the sum of the two appears at both ends of the line as a composite signal, but with time shifts. The sync and burst are used to lock the camera 1, whilst the picture information is taken off at the control unit. <IMAGE>

Description

SPECIFICATION Television systems The invention relates to television systems, and more particularly to transmission of video and synchronisation signals from and to a video source, such as a camera.

According to the present invention there is provided a television signal transmission arrangement comprising a first unit connected by a line to a second unit for connection to a video source, the first unit comprising means arranged in operation to apply synchronising pulses to one end of the line and the second unit comprising means arranged in operation to apply to the other end of line a non composite video signal whereby a combined signal equal to the sum thereof appears on the line, the first unit having means for output of at least the video component of the combined signal and the second unit having means for output of at least the synchronising pulse component of the combined signal for synchronisation of the video source.

It will be appreciated that this arrangement permits the use of a single coaxial cable for transmission of video from a video source (e.g. a camera) adjacent the second unit to the first unit (e.g. a control unit or base unit) and transmission of synchronising pulses in the opposite direction.

Although the invention is in principle applicable to any video source, obviously it is in the case of the camera, with its requirement for mobility, that problems of heavy and expensive cabling arise.

Where power is also to be transmitted, a triaxial cable may be used for all or part of the line.

Multiplexing techniques such as a modulated sub carrier for talkback, and control signals inserted during field blanking, may also be employed.

In a colour television system, colour burst may be transmitted along with the synchronising signals.

In a preferred embodiment, the second unit may include means operable in response to signals from the video source and the combined signal to detect absence of synchronism between the video source and the synchronising signals and thereby suppress application of video to the line until synchronism is attained.

One embodiment of the invention will now be described with reference to the accompanying draw ings, in which: Figure 1 is diagram showing the main parts of a television signal transmission arrangement accord ing to the invention; Figure 2 is a block diagram of the remote unit and triax converter of the arrangement shown in Figure 1; and Figure 3 is a block diagram of the control unit of the arrangement shown in Figure 1.

Figure 1 shows a medium range coaxial triaxial control arrangement for use with a camera 1. A first unit, control unit 2, is linked via a line 3 to a second unit, remote unit 4 connected to the camera 1. If power is available for direct feed to the remote unit 2 and camera 1, then the line 3 to the control unit 4 can be a single coaxial cable. As shown, however, connection is made firstly via a triaxial cable 3A to a triax converter 5, and thence to the control unit 4 via a coaxial cable 3B.

The camera 1 (Figure 2) is of conventional construction. It is of a type (such as the Ikegami HL79A) which has the following inputs and outputs: (a) a standard 75Q composite video output 6.

(b) a genlock input 7 for receiving a video signal to which the internal synchronising pulse generator of the camera is locked. The picture content of this input is ignored by the camera.

(c) an audio input 8, for talkback.

(d) a remote control input 9 with (as shown) fourteen lines.

(e) a 12.5v d.c. power input (not shown).

The remote unit 2 includes a remote video unit 10, in which composite video from the camera output 6 is split into two buffered feeds. One feed supplies a synchronising pulse separator 11 from which the synchronising pulses are used to generate mixed blanking (MB generator 12) and clamp pulses (clamp pulse generator 13). The other feed is clamped (14) and blanked (15) to produce a non-composite output which is fed onto the line 3 via a 75Q line driver 16.

In the control unit 4 (Figure 3), mixed synchronising pulses with colour burst (referred to as "black and burst") from a synchronising pulse generator (SPG) 17 are fed via a subcarrier delay stage 18, for adjustment of the burst phase, and a 75Q line driver 19, to the line 3. In this way, addition ofthe non-composite video from the remote video unit 10 and the black and burst from the control unit 4 produces an apparent composite video signal which is available at both ends of the line 3 (although with a time shift).

Returning now to the remote video unit 10, the line is monitored by a high impedance buffer 20 with a 75Q output which is fed via a 5MHz filter 21 to the genlock input 7 of the camera 1. The camera ignores its own pictures and locks on to the filtered syncs and burst.

To prevent possible confusion of the camera locking system at switch-on, when picture and syncs may overlap, the remote video unit 10 includes a non-lock detector 22 which compares local field synchronising pulses from the sync separator 11 with the remote pulses extracted (in data separator 23) from the signal on the line 3: if a discrepancy exists blanking (in blanking amplifier 15) is extended to suppress the picture information, ensuring the availability of a clean synchronising signal until locking is achieved.

In the control unit 4, the "composite" video from the line is processed by a buffer 24, equaliser 25 (adjustable according to line length) amplifiers 26, 28, and a clamping and blanking stage 27, in which the signal is clamped and re-blanked to produce a non-composite video signal. After filtering (6MHz low-pass filter 29), fresh syncs and burst from the main SPG 17 are added in adder 30 and an amplifier 31 provides the final video output.

Talkback and remote control information are multiplexed onto the line at the control unit by respectively an FM modulator 32 operating at 15MHz and a base station data processor 33 (with control panel 34) which inserts control data during 14 lines of the field blanking period via the line driver 19.

At the camera end, talkback sound is extracted by a subcarriertrap 35 and a 15 MHz FM demodulator 36 and fed to the talkback input 8 of the camera 1.

Control signals are handled, in conventional manner by the data separator 23 referred to above, and a remote data processor 37.

In the triax converter 9, d.c. power is obtained from a mains power supply unit 38 and fed to the inner sheath of the triaxial cable 3A; in the remote unit, power is taken off via a low-pass filter 39, and fed to the battery connector (not shown) of the camera 1. If space permits, the remote unit can be fitted in the camera in place of the battery.

Attention should be given to the timing differences between the video and "black and burst" at the two ends of the line 3, since the syncs and burst must fall within the line blanking period of the camera video signal if degradation of one or other signal is not to occur. In practice, however this does not present any problems and line lengths in excess of 300 metres are found quite practical: for example 100m triax with the balance being coax. Large cable length changes may require adjustment of blanking phase at the camera end.

The system described dispenses with multicore camera cables for most facilities, requiring only a single video tie line to studio floor or other area of operation, thereby offsetting the increasing cost of camera cables in both initial outlay and repair.

Camera modification is (with the camera described) unnecessary.

The control facilities provided on conventional systems can be retained: in addition to those mentioned above, camera microphone or reverse call facilities could be provided. Obviously additional video feeds such as viewfinder mixing, return video or RGB video outputs (as opposed to encoded PAL or other colour signal) would require additional cabling or the use of carriers.

Claims (6)

1. Atelevision signal transmission arrangement comprising a first unit connected by a line to a second unit for connection to a video source, the first unit comprising means arranged in operation to apply synchronising pulses to one end of the line and the second unit comprising means arranged in operation to apply to the other end of line a non-composite video signal whereby a combined signal equal to the sum thereof appears on the line, the first unit having means for output of at least the video component of the combined signal and the second unit having means for output of at least the synchronising pulse component of the combined signal for synchronisation of the video source.

2. A transmission arrangement according to claim 1, in which, for a colour television system, the first unit is arranged to apply colour subcarrier burst signals to the line along with said synchronising pulses.

3. A transmission arrangement according to claim 1 or 2, in which the second unit includes means operable in response to signals from the video source and the combined signal to detect absence of synchronism between the video source and the synchronising signals and thereby suppress application of video to the line until synchronism is attained.

4. A transmission arrangement according to claim 1,2 or 3, in which at least a part of the line, connected to the second unit, is a triaxial cable, and further comprising a power supply unit arranged to supply power via the cable to the second unit.

5. A transmission arrangement according to any one of the preceding claims including means in the first and second units for transmission between them, via the line, of audio and/or remote control signals.

6. A television signal transmission arrangement substantially as herein described with reference to the accompanying drawings.