Blanking interval

from Wikipedia, the free encyclopedia

In television technology, the blanking interval (also called blanking pulse ) describes the time in which the electron beam of a picture tube is switched to dark and returned to the starting point. During this period the image transmission is interrupted ( blanked ). There is the horizontal blanking interval for the path from the end of the line back to its beginning and the vertical blanking interval for the path from the bottom of the picture back up.

Further use

In addition to some synchronization information (to avoid moving images ), the vertical blanking interval has also contained digital data since the 1980s . Most television broadcasters use this area to transmit teletext (introduced in Germany by ARD and ZDF under the name Videotext ), the VPS signal, the electronic program guide EPG and, with the introduction of PALplus , information on the picture format.

Televisions manufactured well into the 1970s were designed in terms of circuit technology so that the "black" blanking interval helped to suppress the beam return. Existing user data at this point are noticeable as image interference. With newer devices only as dancing white stripes on the upper edge of the picture, with older devices the beam return to the upper edge of the picture is partially visible.

With the Sound in Sync method, digital audio information is incorporated into the television signal in the horizontal blanking interval between the image lines .

history

From 1980 the teletext already mentioned was transmitted. Since 1986, data on the broadcast WDR Computerclub have been transmitted using a process called video data . However, the data was placed at the upper edge of the television picture, ie not in the blanking interval itself. From 1990 onwards, computer data was transmitted by the video data channel using this method in the blanking interval. From 1990 onwards he used the TV station ProSieben to transmit data at a speed of 15 kilobits per second in parallel with the television picture.

Another service that took advantage of the blanking interval was Intel Intercast. The content transmitted with Intercast was selected by the respective television broadcaster and complied with the HTML standard. A PC with a TV card and the Intel Intercast Viewer program were required for reception . In the USA u. a. the broadcasters CNN , MTV and NBC provide the service for the transmission of information such as. B. News and stock market data. In Germany, the ZDF has been using this service for free transmission of websites since IFA 1997. At the end of 1998 the pilot project had around 200,000 users. In the same year, German sports television (DSF) also began using Intercast technology. On the basis of good survey results, the ZDF decided in 1998 to extend the project for another year. However, since the selection of websites offered by the television broadcasters was very limited and at the same time the Internet dial-in costs via the telephone line were constantly falling, Intercast technology was soon completely supplanted by Internet access via modem , ISDN and DSL .

Another example of data transmission in the blanking interval was r@dio.mp3 , which, from March 2000 , transmitted music in the form of MP3 files as well as title and cover information instead of teletext on the NBC SuperChannel channel . These could be decoded by PCs with a TV card . The data rate of this service was sufficient to transmit the MP3 files to the recipients in real time at 128 kbit / s. Many users built music collections with additional plugins. The broadcasting operation was stopped in June 2001 after the operator Musicplay GmbH had to file for bankruptcy due to the failure of the necessary follow-up investments in the context of the stock market crash. From April 2002 to April 2003, another broadcaster, Megaradio.mp3 , used this technology. Shortly thereafter, there were various attempts to continue the offer for a fee, but all efforts of the operators came to nothing. The transmission technology used for this is called TV radio cast .

There was trouble in 2003 when Eurosport cooperated with an erotic provider to offer a subscription service for porn films under the name "Sexxxcast.TV" via the blanking interval. Since Eurosport was still represented in the ZDF digital package at the time, there was a lot of commotion (ZDF even threatened to expel Eurosports from the digital package, which happened anyway on January 1, 2006 after changes to the interstate broadcasting agreement) and the cooperation was established after a short time finished again. Resuscitation attempts by the service provider failed. The transmission technology used for this is also referred to as TV radio cast .

See also

Web links

Individual evidence

  1. ↑ Videodat - History, from Hardbitrock to Videodat , archived page from Channel Videodat.