GB1602168A

GB1602168A - System for the transmission of slow-scan television images

Info

Publication number: GB1602168A
Application number: GB12071/78A
Authority: GB
Original assignee: Schraaf Abe V D
Current assignee: Schraaf Abe V D
Priority date: 1977-04-01
Filing date: 1978-03-28
Publication date: 1981-11-11
Also published as: FR2386212A1; FR2386212B3; DE2813973A1; JPS5415611A; NL7703609A

Description

(54) SYSTEM FOR THE TRANSMISSION OF SLOW-SCAN TELEVISION IMAGES (71) I, ABE VAN DER SCHRAAF,of Dutch Nationality, of Rodenrijseweg 555, BERKEL EN RODENRIJS, the Netherlands, do hereby declare the invention, for which I pray that a patent may be granted to me, and the method by which it is to be performed, to be particularly described in and by the following statement:- The invention relates to a system for the transmission of slow-scan television images by using a unit for recording or storing pictures and/or producing image signals, a first coupling device, a communication channel, a second coupling device, a reproduction or storage unit for reproducing or storing the image signals.

Such a system is known in radio-amateur communications.

Slow-scan television (SSTV) is defined as a system of dynamic image transmission, i.e.

images of which the detail may change with time, as distinct from static images encountered in facsimile systems, the image scanning characteristics being chosen such that the original or basic video signal is limited to a video bandwidth compatible with that of normal speech. In order to achieve this reduced bandwidth, the number of frames per second has been greatly reduced.

In the above-mentioned radio-amateur techniques (SSTV), a system for television image recording and reproduction is used in which both the number of images per time unit and the resolution i.e. the number of image lines, are reduced considerably in order to limit the bandwidth required for transmission, to a value compatible with speech, for instance 3 kHz. As an example during the display of SSTV the number of frames may be one per six or seven seconds, with a resolution limited by 120 lines per frame.

The slow-scan TV images can for instance be recorded by flying-spot scanners or vidicon tubes, and the video information then is modulated on a separate subcarrier of say 2 kHz. Both amplitude and frequency modulation are possible and the modulated signal thus obtained has a bandwidth smaller than 3 kHz.

The slow-scan image information can also be recorded on an ordinary cassette or tape recorder, and may be used from this tape in the usual way. This image information may be transmitted by the licensed radio amateur on the allotted amateur frequency bands. After reception the slow-scan TV signals may be converted in an image display unit to produce a picture or may be stored in a normal audio recorder for later use. The image signals can for instance be used to produce a picture by means of a cathode ray tube with extended persistence, or an image-storage tube, or a regular television set (monitor), which has been equipped with an image and storage scanning convertor.

It is an object of the invention to perfect the above-mentioned system in such a way as to make it usable for many important applications in industry and in society in general. This object is attained with the abovementioned system in accordance with the invention by using as communication channel an existing audio channel like a telephone or a radio telephone channel.

According to the present invention there is provided a system for the transmission of slow-scan television images (slow scan television being hereinbefore defined) by means of a recording or storage unit for the recording and/or production of image signals, a first coupling device, a communications channel, a second coupling device, a reproduction or storage unit for the reproduction or storage of the image signals, and wherein the communications channel is an existing audio channel like a regular telephone communication link or radio communication link.

Due to the reduced band width of the slow-scan TV signal, normal telephone lines or radio channels can be used for the transmission and thus many applications become possible, especially control and transmission of information.

In a further advantageous version of the system the first coupling device consists of an electrical-acoustical converter, like a loudspeaker, and the electrical-acoustical converter relevant to the audio communication channel, like a microphone. The second coupling device consists of the electro-acoustical converter relevant to the audio communication channel, like a telephone earpiece, and an acoustical electrical converter, like a microphone.

Alternatively in a further advantageous version the first and second coupling devices in the system each may consist of an electrical connection, whereby the image signal is coupled directly to the telephone line or the input of the transmitter of the radio channel respectively is taken from the telephone line or receiver output of the radio channel.

The invention will now be described by way of example only with particular reference to the accompanying drawings wherein: Figure 1 shows the schematic of a known recording device with flying-spot scanner or vidicon tube; Figure 2 shows the schematic of a known reproducing unit with a cathode ray tube or storage tube; Figure 3 shows the system according to the invention, in which the slow-scan TV signals are transmitted through a normal telephone line; and Figure 4 shows the system according to the invention, in which the slow-scan TV signals are transmitted through a normal radio communications channel.

In Figure 1 a known circuit for recording slow-scan images is shown, in which lisa flyingspot scanner or vidicon tube, 2 is a sawtooth generator, 3 is a synchronisation circuit, 4 is an amplifier, 5 is a 2 kIt: oscillator and 6 is a modulator. The output of the circuit is 7a where the video information is supplied in the form of the slow-scan TV signal.

In Figure 2 a known circuit for the reproduction of slow-scan TV signals 7b is shown, in which 8 is an amplifier, 9 is a filter circuit, 10 is a synchronisation circuit, 11 is a sawtooth generator and 12 is a cathode ray tube with extended persistence or storage tube. For extended persistence P7 type phosphors for example may be used.

Figure 3 shows the system according to the invention. From a camera 1 or a cassette or tape recorder 13 the slow-scan signal is fed to unit 14 which may be part of the circuit of Figure 1. The output signal 7a of unit 14 is fed to a first coupling device 15, consisting of loudspeaker 16 and microphone 17 which is part of a regular telephone line 18. At the end of the telephone line the signal is fed to the second coupling device 19 through the earpiece 20 to the microphone input 21 of the reproduction or recording part of the system.

The signal 7b is fed via amplifier 22 to the reproduction unit 12 or recorder 13. Alternatively the first coupling device 15 and/or the second coupling device 19 may consist of a direct electrical connection 24, 25 connected directly to the telephone line.

Figure 4 shows another implementation of the invention, in which the slow-scan signals are being transmitted through a radio telephone or walky-talky unit 26 in lieu of a telephone line.

Here again the first coupling device 15 may consist of a loudspeaker 16 and a microphone 17, or of a direct electrical connection 24 to feed the signal 7a to the input of the transmitter 27 of the radio telephone. The second coupling device then can consist of the loudspeaker output 20 of receiver 28 and the microphone input 21 of the remainder of the circuit, or of a direct connection 25 between the receiver output and the input of the remainder of the circuit. Especially in the case ofhigh signal-to-noise ratios in the image information a direct connection may be of advantage.

It is also possible, for instance by means of a flying-spot scanner, to transmit colour information by using three colour filters (redgreenblue) at the transmit as well as the receive end, whereby three successive frames are transmitted with different colour filters.

The system as described above can be used for many applications in the field of control and monitoring, and transmission of information. For instance all sorts of drawings, photographs, life pictures of damage, security, industrial processes, etc. can be transmitted through normal telephone lines or radio telephone connections. In the field of shipping pictures of storm damage, technical defects, sickness effects of patients on board for diagnosis on land can be transmitted by the use of marine radio telephone. In aviation applications may include hijacking attempts, security on board, testflights, technical defects, etc. that can be transmitted by use of normal radio communication channels to the ground, and conversely documents may be shown from the ground to the airplane.

For application in the field of police work many possibilities are present. Patrolcars or separate units for crime prevention may exchange slow-scan TV images through existing telephone or radio communication channels.

The system is also fit for private use, by using existing telephone lines in lieu of the more expensive broadband lines for the exchange of pictures.

Claims

WHAT I CLAIM IS:

1. A system for the transmission of slow-scan television images (slow scan television being hereinbefore defined) by means of a recording or storage unit for the recording and/or production of image signals, a first coupling device, a communications channel, a second coupling device, a reproduction or storage unit for the reproduction or storage of the image signals, and wherein the communications channel is an existing audio channel like a regular telephone communication link or radio communication link.

2. A system as claimed in claim 1, wherein the first coupling device consists of an electricalacoustical converter, like a loudspeaker, and the acoustical-electrical converter relevant to the existing audio channel, like a microphone, and that the second coupling device consists of the electrical-acoustical converter relevant to the existing audio channel, like a telephone earpiece, and an acoustical-electrical converter, like a mircophone.

3. A system as claimed in claim 1, wherein the first and/or the second coupling device consist of a direct electrical connection, by which the television signal is applied directly to the telephone communication or transmitter input of the radio communication respectively is taken from the telephone communication or receiver output of the radio communication.

4. A system for the transmission of slowscan television images (slow scan television being hereinbefore described) substantially as hereinbefore described and as shown in Figures 3 or 4 of the accompanying drawings.