Slow scan television!
SSTV is a method for transmitting images that was pioneered by ham radio operators. It transmits images using a very narrow bandwidth, approximately the same as a single sideband (SSB) voice signal - 3 kHz. It is essentially a translation of image data into audio tones that can be transmitted over the radio, and then back into images.
Why is this a big deal? First, because normal, moving television images require signals with a bandwidth 2,000 times larger (6 MHz). This saves a huge amount of spectrum space, making this mode usable on lower frequencies (HF/VHF) and not just restricted to higher frequencies. SSTV is also cheaper - you aren't operating microwave transmitters and drawing thousands of watts to transmit your signal. You can use existing equipment and radio transceivers designed for SSB voice signals at a bandwidth of 3 kHz. This makes it easy to receive an SSTV signal with a VHF radio and pipe it over to a sound card for slow scan TV software to take over.
The technology dates back to 1968, when amateurs were first granted spectrum space to do slow scan TV. Slow scan TV was also utilized during the Apollo lunar missions.
You can find a sample of what slow scan TV signals sound like here: File:JupiterSSTV.wav
Or watch SSTV in action in the video below:
qsstv is a Linux utility for turning SSTV signals into images and vice-versa. Nice user interface with a waterfall spectral display, and many different schemes available.
SSTV for Android
Qsstv can also be done with an Android phone. Using the Robot36 app (Robot36 is a modulation scheme for SSTV, although the app is capable of decoding other schemes) allows you to turn SSTV signals captured through the Android phone's microphone into SSTV images. Here's a video of that in action:
SSTV (slow scan television)a method for sending television and static images using 1,000 times less bandwidth than a television signal.
Slow scan television: SSTV
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digital modesdigital modes for radio communications.
TNC modem for Raspberry Pi: RaspberryPi/TNC-Pi
Tinytrak replaces TNC modem for APRS devices: Tinytrak
Linux software master list: Andys Ham Radio Linux
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