What is SSTV?
Slow Scan Television or 'SSTV' is a way of sending images over a radio link using audio. It is not like television in the conventional sense because each image takes many seconds to arrive. SSTV's advantage is that it is a narrow-band mode, and so images can be transmitted around the world on the HF bands.
Getting Going on SSTV
As a relative newcomer to amateur radio, I was surprised how easy it was to start receiving SSTV images. During the daytime, 14230 MHz on the 20m band is a popular place to find SSTV signals. Apart from the rig, all that is needed is a PC running a freeware package called MMSSTV (see software section (links to Software heading further down the page) below). Ideally some method of connecting the audio from the rig to the mic input or line input on the PC soundcard is needed, but if no leads are available it is still possible to receive images if the PC has a microphone by simply letting the PC "hear" the sound from the rig. A much better solution is a dedicated, isolated, wired connection. The isolation often takes the form of a transformer for the audio, and an opto-isolator for the PTT line (when transmitting images). Isolation prevents earth loops (hum) and helps to prevent digital noise from entering the rig, and RF entering the PC\laptop. Setting up MMSSTV is easy, especially as a number of "Auto" options are provided (eg for detecting the sending mode).
Images can also be transmitted using MMSSTV. Transmitting pictures is somewhat more complex, because some way of controlling the PTT is needed. There are also different formats for SSTV signals - "Martin 1" might be a good starting point. Audio levels need to be set correctly and any speech processors turned off. Be familiar with the techniques and conventions used for SSTV QSOs before sending the first image, so as not to upset other amateurs. There are many web sites describing setting up an SSTV station using the MMSSTV software, try entering "MMSSTV" in your favourite search engine.
Strictly speaking 14230MHz on the 20m band should be used like a calling channel. Users should first check that the the frequency is not in use before making a CQ call by voice (microphone). Once contact is established, users should QSY up or down by 3kHz to an unused frequency before sending their images.
Unfortunately this practice is not always followed, with many QSOs taking place on 14230. For newcomers, however, this has the advantage that tuning to 14230 will be a good starting place to receive a first image.
MMSSTV can be found here:
- MMSSTV (links to http://hamsoft.ca/pages/mmsstv.php)