"Digital comms" in the (amateur) radio world is analgous to a fax machine or radioteletype. Everyone's used a fax machine before - it encodes an image of a page into sound tones that you send over the phone, and a machine on the other end decodes the sounds tones back into an image of the page. Amateur radio "digital modes" are very similar, except that mostly, your machine (the TNC or terminal node controller, usually in the form of software for your PC and maybe a sound card) converts typed text to sound tones which you transmit over the air, and then decode into typed text again on the other side.
FLDIGI is a free download that will give you a lot of capability. You can download it and just experiement with it, playing the sound tones over your computer speaker. FLDIGI does PSK31 and CW (morse code), RTTY, and many other modes.
One of my radio friends recently brought up the JT65 mode. This mode isn't supported by FLDIGI, but there is a free download, WSJT, which does. After listening to examples of this mode, I realized I'd been hearing it on some of the shortwave bands like 20m and 40m, and just hadn't known what it was.
JT65 is intended for very low SNR type message passing. Reading through it's help file, the QSOs they show as examples are very short!
Sunday, August 30, 2015
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