Slow-scan television
Slow-scan television (SSTV) is a picture transmission method, used mainly by amateur radio operators, to transmit and receive static pictures via radio in monochrome or color.
A literal term for SSTV is narrowband television. Analog broadcast television requires at least 6 MHz wide channels, because it transmits 25 or 30 picture frames per second (see ITU analog broadcast standards), but SSTV usually only takes up to a maximum of 3 kHz of bandwidth. It is a much slower method of still picture transmission, usually taking from about eight seconds to a couple of minutes, depending on the mode used, to transmit one image frame.
Since SSTV systems operate on voice frequencies, amateurs use it on shortwave (also known as HF by amateur radio operators), VHF and UHF radio.
History[edit]
Concept[edit]
The concept of SSTV was introduced by Copthorne Macdonald[1] in 1957–58.[2] He developed the first SSTV system using an electrostatic monitor and a vidicon tube. It was deemed sufficient to use 120 lines and about 120 pixels per line to transmit a black-and-white still picture within a 3 kHz telephone channel. First live tests were performed on the 11-meter ham band – which was later given to the CB service in the US. In the 1970s, two forms of paper printout receivers were invented by hams.
Encoded image in B/W 8 system.
An SSTV image received by an amateur station transmitted from the ISS using the PD-120 mode.
The resulting picture following decoding of the sample SSTV transmission.
A Spectral Analysis of the sample SSTV transmission
In popular culture[edit]
In Valve's 2007 video game Portal, there was an internet update of the program files on 3 March 2010. This update gave a challenge to find hidden radios in each test chamber and bring them to certain spots to receive hidden signals. The hidden signals became part of an ARG-style analysis by fans of the game hinting at a sequel of the game – some sounds were of Morse code strings that implied the restarting of a computer system, while others could be decoded as purposefully low-quality SSTV images. When some of these decoded images were put together in the correct order, it revealed a decodable MD5 hash for a bulletin-board system phone number (425)822-5251. It provides multiple ASCII art images relating to the game and its potential sequel.[10][11][12] The sequel, Portal 2, was later confirmed. According to a hidden commentary node SSTV image from Portal 2, the BBS is running from a Linux-based computer and is linked to a 2,400 bit/s modem from 1987. It is hooked up in an unspecified Valve developer's kitchen. They kept spare modems in case one failed, and one did. The BBS only sends about 20 megabytes of data in total.
In the aforementioned sequel, Portal 2, there are four SSTV images. One is broadcast in a Rattman den. When decoded, this image is a very subtle hint towards the game's ending. The image is of a Weighted Companion Cube on the Moon. The other three images are decoded from a commentary node in another Rattman den. These 3 images are slides with bullet points on how the ARG was done, and what the outcome was, such as how long it took the combined internet to solve the puzzle (the average completion time was 7 1/2 hours).[13]
In another video game, Kerbal Space Program, there is a small hill in the southern hemisphere on the planet "Duna", which transmits a color SSTV image in Robot 24 format. It depicts four astronauts standing next to what is either the Lunar Lander from the Apollo missions, or an unfinished pyramid. Above them is the game's logo and three circles.[14] It emits sound if an object is near the hill.
Caparezza, an Italian songwriter, inserted an image on the ghost track of his album Prisoner 709.
The Aphex Twin release 2 Remixes by AFX contains a track that displays an SSTV image that has text about the programs used to make the release as well as a picture of Richard sitting on a couch.
Modem software: