Slow Scan TV - pictures over radio

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.

SSTV uses analogue frequency modulation, in which every different value of brightness in the image gets a different audio frequency.

In other words, the signal frequency shifts up or down to designate brighter or darker pixels, respectively. Colour is achieved by sending the brightness of each colour component (usually red, green and blue) separately. This signal can be fed into an SSB transmitter, which in part modulates the carrier wave. (There is also a digital SSTV mode - details at a later time.)

There are a number of different modes of transmission, but the most common ones are Martin M1 (popular in Europe) and Scottie S1 (used mostly in the USA). Using one of these, an image transfer takes 114 (M1) or 110 (S1) seconds. Some black and white modes take only 8 seconds to transfer an image.

Where to find SSTV activity

Using a receiver capable of demodulating single-sideband modulation, SSTV transmissions can be heard on the following frequencies:

Software

• Windows
  • MMSSTV
  • RXSSTV (RX only)
  • MultiPSK
• Linux
  • QSSTV
• MacOS
  • MultiScan 3B
• Android
  • DroidSSTV
  • Robot36
• iOS
  • SSTV Slow Scan TV

Recieve SSTV without a radio

If you have not got an HF receiver then use an Software Defined Radio, or a WebSDR. Windows, Mac, and Linux can be configured to route audio between applications using aVirtual Audio Cable, allowing SSTV decoing without the use of HF transciever.

Sample Image

The above image can be reproduced with this MP3 file when played in to a suitable SSTV decoder. The video below shows the decoding process in MMSSTV.