I find this an article I read in Radio World to be absolutely fascinating. It’s called “Radiogram” and it basically is a method of embedding webpage like content within a tone via an shortwave AM broadcast!
No internet connection or special equipment is needed to receive or decode the signal other than a standard shortwave receiver and a computer or smartphone.
Below I’ve copied and pasted the highlights from the full article at http://www.radioworld.com/default.aspx?tabid=75&entryid=10210
..They want to draw attention to VOA Radiogram, a form of international high-frequency broadcasting. Radiogram is a VOA program experimenting with digital text and images via shortwave broadcasting;
Radiogram broadcasts Web content via error-detecting/correcting AM tone modulation, using standardized formats commonly used by ham radio. They say this approach is robust and resistant to interference.
“The user’s ordinary shortwave receiver, tuned to a Radiogram transmission, feeds its audio to a user device. These could include mobile phones, tablets, laptop and desktop computers and the new ARM-based miniature computers and embedded devices. The user device decodes the tones and displays text and imagery despite propagation impairments and intentional interference — and without Internet connection.”
They point out that no hardwire connection is required; putting the radio near the phone or computer is usually sufficient. “By adding a simple audio cable between receiver and user device, however, reception can be silent and covert. No specialized hardware is needed, and the software platform for decoding is long in the public domain.”
The user need not be present to receive content, and essentially receives a web magazine “updated at will and always ready for use” that can be redistributed.
“Naturally, the audio tone transmission can be recorded for later playback. Even when buried well under music or noise, the nearly inaudible recorded broadcast can nevertheless deliver 100% copy upon decode. “
Radiogram’s transmission methods provide text at 120 words per minute, along with images.
“Sent over regular broadcast transmitters (no modifications needed), this approach effectively extends the reach of the transmitter. In other words, the digital text mode will decode in locations where the audible speech over the same transmitter would be too low for aural intelligibility. The audio recorded or captured could be replayed over another transmitter to even further extend the reach of the broadcast.”