Seeing Things on Your Ham Radio: Image Communication
Don’t hams care about pictures and graphics? They do! With the increasing availability of excellent cameras and computer software, getting on one of the amateur image modes has never been easier.
The ease of image communication has resulted in several really interesting uses, such as sending images from balloons and radio-controlled vehicles. In addition, emergency communications teams are starting to use images as tools for assessing damage after a disaster or managing public events. The ARRL Handbook and The ARRL Operating Manual both have a chapter on image communication.
Slow-scan television and facsimile
You can find slow-scan television (SSTV) primarily on the HF bands, where SSB voice transmission is the norm. The name comes from the fact that transmitting the picture over a narrow channel made for voice transmissions takes several seconds. Usually, you can hear slow-scan signals in the vicinity of 14.230 and 21.340 MHz by using USB transmissions.
SSTV enthusiasts start with a webcam or video camera and a sound card. They use frame-grabber software to convert the camera video to data files. Graphics files from any source can be used. SSTV software encodes and decodes the files, which are exchanged as audio transmitted and received with a voice SSB transceiver. You can use analog SSTV, in which the picture is encoded as different audio frequencies, or digital SSTV, in which the picture is broken into individual pixels and transmitted via a digital protocol.
Facsimile over radio is still a widely used method of obtaining weather information from land-based and satellite stations. Hams rarely transmit fax signals anymore, but it’s handy to be able to receive fax transmissions.
You can also send full-motion video, just as regular broadcasters do, with fast-scan video transmissions. Fast-scan uses the same video standards as analog broadcast and consumer video, so you can use regular analog video equipment. This mode is usually called amateur television (ATV) and is most popular in metropolitan and suburban areas, where transmission distances are relatively short. ATV even has its own repeaters.
The Ham TV website has lots of resources for ATV. It includes sections on using ATV to beam back photos from RC-controlled planes and drones, balloons, and rockets.
ATV transmissions are restricted to the 440 MHz band and higher frequencies because of their wide bandwidth — up to 6 MHz. You won’t be able to use your regular 70 cm transmitter to handle that bandwidth, so you must construct or purchase a transmitter designed specifically for ATV. The transmitters are designed to accept a regular video camera signal, so little extra equipment except a good antenna is required to use ATV.
Many ATV transmissions use the same video transmission format (called NTSC) that analog TV broadcasts did. That means old analog television receivers can be used as receivers. A frequency converter is used to transfer the ham band ATV signals to one of the higher UHF TV channels, where they’re received just like any other TV signals.
Hams are also using the same types of signals as digital TV broadcasts or DTV. As of late 2017 more surplus equipment has become available and hams are migrating to DTV formats. There are repeaters for DTV, too. The DATV-Express project is working to develop and produce inexpensive DTV equipment that doesn’t rely on the availability of broadcast industry surplus. This is an active area of experimentation so expect the situation to change.