Narrow Bandwidth Television
The narrow-bandwidth television ( NBTV ; German narrowband television ) originated out an adaptation of the first television experiments of the 1920s and 1930s (see also. Mechanical television for) amateur radio . The big advantage is that the television pictures are in very low resolution, e.g. B. in the old English standard according to John Logie Baird, which is still common today, is only 30 lines at 12.5 frames per second, or in a variant that is more widespread today, the NBTV standard, 32 lines. This results in a maximum requirement for the bandwidth of 32 lines × 48 pixels per line × 12.5 images = 19,200 pixels, i.e. 9,600 Hertz . Since less information is transmitted in practice, a normal shortwave channel is sufficient for transmission, which makes this technology still interesting for amateur radio today. The images have a low resolution, but in contrast to the higher resolution SSTV , moving images can also be transmitted.
The definition of the so-called NBTV standard is 32 lines, vertical, scanning from bottom right to top left (without interlacing), aspect ratio 3: 2 ("portrait format"), 12.5 images per second.
Today, digital processes are used for the transmission and recording of color images. These are broken down into the three basic colors and transmitted either to the (mechanical) television set or to a PC for reproduction .
Regular broadcasts can be observed above all in the 80 meter band (around 3700 kHz) in the AM modulation type outside of the usual "peak hours", there are occasional broadcasts in other frequency ranges and in purely digital form.
Nowadays, no special television sets are used to decode and generate the images, but rather computers . (In the case of digital forms of NBTV, a computer is even a prerequisite.) There are, however, a growing number of fans and hobbyists of mechanical and fully electronic televisions who specifically use either historical receivers or such (sometimes with the help of modern means such as light emitting diodes and transistor amplifiers ) recreate.
Web links
Individual evidence
- ↑ Archived copy ( Memento of the original from December 26, 2012 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. Frequencies for non-voice ham modes
