Slow-Scan Television (SSTV)
SSTV is a mode that uses a computer and an amateur radio transceiver to send and receive still images over radio. SSTV was originally an analogue mode based on Frequency Modulation (FM). Digital SSTV has become possible with little trouble in recent times with the use of Digital Radio Mondiale (DRM). Despite the name "television", SSTV cannot send or receive moving pictures; it is more akin to sending a FAX.
For SSTV to work, an image is "broken" into lines, composed of dots of colour and light intensity known as pixels. Each pixel is given a specific audio frequency ( that modulates the carrier) depending on its brightness. In a colour image, each of the primary colours, red green and blue are analysed for brightness.
The lines of a picture are scanned from left to right. The modulating frequency varies between 1500Hz and 2300 Hz. There are a number of modes used for SSTV - see below for information. Computer software attaches a Vertical Interval Signaling (VIS) code at the start of a picture being sent. this enables receiving software to determine which mode is being used, and hence permits successful decoding of the signal.
The colour and brightness information modulates a carrier wave for transmission. A remote station picks up the signal and a computer is used to re-create the picture from the FM signal.
SSTV should not be confused with amateur Fast-Scan Television, often simply called Amateur Television or ATV.
- 1957 - Copthorn Macdonald develops the fundamental concepts behind SSTV
- 1958 - First Electrostatic P7 monitor built by Macdonald
- 1958 - Macdonald creates the first SSTV Camera using special Westinghouse 7290 vidicon
- 1960 - FCC Grants a Special Temporary Authorization (STA) to send SSTVG in the USA, limited to those who Macdonald had given 7290 vidicons
- 1967 - Magnetic Deflection, transistorized P7 monitor was developed
- 1968 - WB8DQT & K7YZZ develop and build the "Flying Spot Scanner"
- 1968 - SSTV with standard vidicons, WB8DQT, K7YZZ
- 1968 - FCC makes SSTV legal for advanced class hams (USA).
- 1969 - W9NTP builds the sampling camera
- 1970 - W7FEN uses double sideband SSTV providing simultaneous voice and SSTV (voice on lower sideband, SSTV on upper sideband) for the first time
- 1970 - WB8DQT, W2DD send the first color SSTV pictures using Polaroid camera, RGB filters and Py monitors -
- 1970 - First commercial SSTV system with Robot 70 monitor & Robot 80 camera
- 1971 - W7ABW uses plumbicons from TV stations for the SSTV camera
- 1972 - W0LMD builds the first SSTV keyboard integrated circuit unit
- 1972 - W9NPT,WB8DQT publish the "SSTV Handbook",
- 1973 - W6MXV & W0LMD build a Camera Scan Converter using a TV camera
- 1973 - W9NTP & SM0BUO use Double vidicon tubes to provide bright SSTV pictures on TV monitors
- 1974 - WB9LVI, W6MXV, &W0LMD build the Receiving SSTV Shift Register Scan Converter
- 1975 - W9NTP develops the three color shift register scan converter,
- 1975 - Robot 300 is achieved using Princeton vidicons
- 1976 - W9NTP uses colour wheel filters for SSTV receive/transmit Scan Converter
- 1976 - W9LMD, WB9LVI build RAM SSTV scan converters\
- 1976 - Solid state RAM Robot 400 obsoletes Robot Model 300
- 1977 - W0LMD uses a Persona Computer 1st used to send & receive SSTV
- 1978 - FCC grants KHZ, W0LMD Special Temporary Authorization (STA) to send Medium Scan Television
- 1979 - W0LMD achieves the 1st moving TV from USA to Europe without cable or satellite
- 1980 - W0LMD develops ingle frame color
- 1984 - Robot 1200 provides commercial single frame color, Multiple Analog Components (MAC) method
- 1984 - K6AEP, WB8DQT achieve SSTV using the Radio Shack Color Computer
- 1993 - Pasokon PC based software & hardware boards for SSTV
- 1995 - PC DOS based software & an operational amplifier interface for SSTV marketed
- 1997 - PC Windows & Sound Blaster based SSTV software marketed
A number of SSTV modes are available for amateurs to use. The most popular at time of writing (Feb 2008) are AVT, Martin, Robot and Scottie. More information on the characteristics of these modes can be found here.
Brief details of scan time, lines and colour transmission of some modes can be found on thisSSTV Modes wiki page.
SSTV Nets and Frequencies
Click here SSTV frequencies for an up-to date list
Related wiki page SSTV software
- MMSSTV for windows computers. A versatile and easy to use program. It can handle all the common modes, but users have access to a number of lesser used modes such as MP73-N which is allowing amateurs to use sstv on the 30m band where previously it was restricted by band definitions.
- QSSTV for Linux users. This is a relatively new program. The source code is available under the GNU license.
SSTV webcam page - how to
SSTV Webcam pages are used to show other hams what pictures have been received over a period of time at your shack. They are quite straightforward to create and plenty of help is available online. Firstly, join the FTP_widget Yahoo group. Members have access to html code for web pages. Use a website tool such as Dreamweaver to create a webcam page, and then add the html code from the yahoo group to it. An example of a page using this code can be found here. Upload the webcam page into your website. Next, download the ftp widget from KE5RS, and install it it on your PC. This widget collects pictures from a nominated folder and uploads them into the webcam page. The yahoo group also offers a good pdf tutorial on how to configure the widget for MMSSTV. The software runs only on PC's.
World SSTV webcams can be found with the links below:
- from CX2APB webcams from around the world
- from KE5RS more webcams from around the world
- from VK2QQ - a mixture of Australian and world webcam
- from VK4YEH Australian webcams
HTML code for an SSTV page can be found here. Scroll down to "other Files" for the link.
SSTV with a Macintosh computer
This article describes the use of a 1,8GHz G5 with1.5GB Ram and running OS 10.4.11. This machine comes with the facility to run two monitors, which proved to be very useful for SSTV.
Hardware Apart from the computer, an interface between computer and radio is required. Two commercially available interfaces have been used successfully with the computer described above and a Yaesu-FT-897, but undoubtedly others will work just as well. The Digimaster from ZLP Electronics and the Signalink USB from Tigertronics are both plug and play devices.
Setup Two monitors were used in this setup. Macrobot proved to be much easier to use for TX, whereas Multimode proved to be better for RX. This is because Macrobot did not seem to be as sensitive to weak signals and so RX detection stopped when the signals varied in strength. This problem was never resolved by the writer, hence the use of both software programs. The TX interface and setup in Multimode was not found to be as easy to use as for Macrobot.
|Modes of operation
|CW * AM * FM * SSB * Digital * Echolink * Emission Classification * IRLP * Optical communications
|APRS * D-Star
|SSTV and ATV
|SSTV frequencies * SSTV Modes