SSTV

    SSTV ("Slow Scan Television") allows the user to send fixed pictures (in general in colors), with a bandwidth similar to the one of HF Fax (« shift » of 800 Hz, white at 2300 Hz and black at 1500 Hz). Different SSTV modes are proposed,

    This mode is included into the software MULTIPSK by Patrick F6CTE, there is the description of this mode and its variants as well as the specifications coming from his software :



The SSTV ("Slow Scan Television") allows the user to send fixed pictures, in colors or in grey scales, with a transmission band similar to the one of HF Fax (« shift » of 800 Hz, the white at 2300 Hz and the black at 1500 Hz). Different SSTV modes exist.
SSTV is, as Fax mode, an analog mode, not a digital mode.

In SSTV "grey scales" (as in B/W24), frequencies are situated between 1500 and 2300 Hz from the black (1500 Hz) to the white (2300 Hz). In a color picture, the grey nuance is defined as equal to the mean value between the three fundamental color levels (green, red and blue).

For example for the "B/W 24" mode, the picture is defined on a width of 320 columns and a height of 240 lines. In this mode, the following are sent successively:

* the VIS code for B/W24: this binary code allows to define the used mode. It is available for classical modes as Martin 1 or Scottie 1. The bit "0" is defined by a frequency of 1100 Hz and the bit "1" by a frequency of 1300 Hz. Therefore starting from a state when the mode is unknown, the VIS code will allow to define it.
* a synchronization signal of 7 ms long at 1200 Hz,
* a transmission of 93 ms long to define the grey level.
* this process is repeated (synchronization then grey level) for each of the 240 lines. So the transmission of a picture is 24 seconds long.

Note 1: for a better appearance, the grey level is computed according to a "physiological" formula:
 Grey level = 0,30 x Red level +  0,59 x Green level + 0,11 x Blue level
Note 2: 256 grey nuances are distinguished which is sufficient.

In SSTV "color" (as in Martin1), the color of each pixel is defined from the fundamental colors, the proportion of each of these three components allows to define a big number of colors (256x256x256).
As an example of color mode, we can start with the "Martin1" mode, where the picture is defined on a width of 320 pixels and a height of 256 pixels. In this mode are sent successively:

* the VIS code for Martin1,
* a synchronization signal of 5 ms long at 1200 Hz,
* a passage of 147 ms long to define the green level,
* a passage of 147 ms long to define the blue level,
* a passage of 147 ms long to define the red level. Here, the line is complete,
* this process is repeated (synchronization, green, blue, red) for each of the 256 lines. So the transmission of a picture is 114 sec long.

The modes proposed by the author are the following:
* Martin 1: color mode, transmission time: 114 sec,
* Martin 2: color mode, transmission time: 58 sec,
* Scottie 1: color mode, transmission time: 110 sec,
* Scottie 2: color mode, transmission time: 71 sec,
* Scottie DX: color mode, transmission time: 268 sec,
* Robot 36: color mode, transmission time: 36 sec,
* Robot 72: color mode, transmission time: 72 sec,
* B/W 24:  grey scales mode, transmission time: 24 sec,
* PD 50: color mode, transmission time: 50 s,
* PD 90: color mode, transmission time: 90 s,
* PD 120 (RX only): color mode, transmission time: 126 s,
* PD 180 (RX only): color mode, transmission time: 187 s,
* PD 240 (RX only): color mode, transmission time: 248 s,
* SC2 180: color mode, transmission time: 182 s.


Notes:

* Martin and Scottie modes are all in a picture format of 320x256, the others in 320x240,
* Martin modes have been developped by Martin Emmerson G3OQD,
* Scottie modes have been developped by Eddy Murphy GM3BSC,
* SC2 modes have been developped by Volker Wraase,
* the B/W 24 and Robot 36/72 are modes developped by the firm "Robot" (USA),
* the PD modes have been developped by Paul Turner (G4IJE) and Don Rotier (K0HEO) in 1996,
* S/N ratio must be high (>0 dB) to distinguish the picture.

Recommanded frequencies for SSTV
3730 (LSB), 7035 (LSB), 14230 (USB), 21340 (USB), 28680 (USB), 144500 (FM) kHz