HF digital modes
Have you ever chatted via keyboard to people over the Internet? If so, you have a fair idea of what it's like to operate via digital modes such as radio teletype, AMTOR and PSK-31. The main difference is that instead of using a phone line or a broadband connection, supported by millions of dollars worth of cabling, routers and undersea cables, multiple ISPs and a lot of support staff, you're using a radio link and connecting directly with the other station via probably several hundred dollars worth of your own radios.
Smart software and sound-card equipped PCs has made it possible for one to link computers to transceivers without needing a sophisticated modem box in between. The result of these developments has been a tremendous growth in modes such as PSK-31. Digital modes take up very little space on the radio bands, much less that what's required for voice communication. This makes it possible for amateurs with low power and restricted antennas to achieve communications not possible with voice modes. PSK-31 is so efficient that an American kit manufacturer has developed a two-watt transmitter that allows world-wide communication from almost anywhere when plugged into a laptop computer. Most PSK-31 activity is around 14.070 MHz, but the mode also has potential for weak signal VHF/UHF work. PSK-31 is most suited for one-on one keyboard communication.
Modes such as AMTOR and PACTOR are other digital modes popular on HF. These are also effective weak signal modes (much more so than packet radio). PACTOR bulletin board systems on HF linked to VHF bulletin boards using packet radio allow stations beyond the reach of VHF packet radio to send and receive messages. An example of such a system is the VK5BAR station operated by the Adelaide Hills Amateur Radio Society.
There is a lot of information available on the internet about these modes and rather than trying to summarise this wide field here, it's suggested you research these modes using your favourite search tools.
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