Slow Scan Television
Slow Scan Television (SSTV) is an analog operating mode in the amateur radio service and is used for the transmission of still images.
functionality
The transmission speed of amateur radio faxes is quite low with a high resolution, so that in 1958 Copthorne Macdonald developed a method in the USA to transmit images faster. In German, SSTV is called narrow band television and can e.g. B. transmit multiple black and white images. This is pretty simple, you only need a video camera and a memory converter or a corresponding PC program that converts the video signals into tones that are analogous to brightness, which are then sent to the transmitter. At the receiver, these signals are simply converted back and made visible as a still image on a monitor.
In the analog operating mode SSTV, the image is scanned line by line. The brightness controls the frequency of an AF generator. 1500 Hz corresponds to black and 2300 Hz to white. The sampling in the transmitter and receiver is synchronized by a 1200 Hz clock signal.
The German SSTV pioneer Volker Wraase, DL2RZ, developed a line-sequential color image process that, in a modified form, represents the transmission standard commonly used today. Here the image is broken down into three color separations, which are sent line by line in the sequence red, green, blue. The transmission standard that is decisive today is based on the development of Martin Emmerson, G3OQD. The transmission of a "Martin-1" picture takes 114 seconds and represents a good compromise between transmission time and resolution.
SSTV is the narrow-band preliminary stage to broadband amateur radio television (over 7 MHz bandwidth ). SSTV has a bandwidth adapted to the voice channel (below 3 kHz) and is suitable for sending pictures on shortwave. But also on the VHF bands there are meeting frequencies for image exchange, and special SSTV relays output a stored image after a short pause on the same frequency (e.g. for quality control). SSTV can also be operated in the PC with the help of computer sound cards and special programs (e.g. JVComm from Eberhard Backeshoff, DK8JV).
SSTV images are occasionally - mostly for anniversary celebrations - also transmitted from the International Space Station. Reception is also possible via a DVB-T stick in conjunction with the appropriate software. It is only recently that there have also been digital successors for SSTV in amateur radio. The scanning in the PC does not take place here in real time, but with a high level of error security. A program that makes this thing useful is DIGTRX, for example. In addition to image files, it can also be used to transfer text files that are transmitted as sound in the voice channel. This even works with acoustic coupling (hold microphone to loudspeaker). These new digital data transmission modes as well as MFSK , HamDREAM and MT63 are not compatible with the analog SSTV modulation.
Sound samples
(M1 method, 1:59 min, 736 kB, OggVorbis)
Frequencies
In the band plans , the following simplex frequencies are provided for SSTV in amateur radio:
| 80 m | Fashion |
|---|---|
| 3725-3740 kHz | LSB |
| 40 m | Fashion |
| 7050-7060 kHz | LSB |
| 20 m | Fashion |
| 14.225-14.235 MHz | USB |
| 15 m | Fashion |
| 21.335-21.345 MHz | USB |
| 10 m | Fashion |
| 28.675-28.685 MHz | USB |
| 2 m | Fashion |
| 144.500 MHz | USB |
| 70 cm | Fashion |
| 432.500 MHz | USB |
| 23 cm | Fashion |
| 1,296.500 MHz | USB |
The following frequencies are used in CB radio:
| 11 m | Fashion |
|---|---|
| 27.235 MHz (24) | FM / USB |
| 27.305 MHz (30 for DX) | FM |
See also
literature
- Copthorne Macdonald: A New Narrow-Band Image Transmission System . In: QST . August 1958, p. 11-15, 140, 142 (English).
- Copthorne Macdonald: A New Narrow-Band Image Transmission System . In: QST . September 1958, p. 31-36, 146, 148 (English).
- Rick Booth: The Beat of A Different Drum: The Cop MacDonald Story. In: QST . January 1993, p. 31 (English).
Web links
Individual evidence
- ↑ SSTV images from the ISS. www.Afug-Info.de, 2015, accessed in 2015 .