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Digital Communications
Sound Card Software
Computer is hooked directly to radio
Received audio is fed to sound card and processed by the computer. Received digital signals are displayed on screen
Transmit audio is generated by the computer via sound card to transmitter. Data may be from “text” file or keyboard
Computer “keys” transmitter via serial port
See AFF2K website for more details (www.qsl.net/afa2ts/aff2k/aff2k.htm)
Notes:
Now we come to the last approach to going digital. This is the use of the PC soundcard. This is a very powerful approach. It is best witnessed by the growth in the mode PSK31 (that is phase shift keying) on the amateur bands. (We do not use that mode in USAF MARS.) We do use MFSK16 (multiple frequency shift keying-16 tones). In this mode, the digital data is encoded in the keying of 16 closely spaced tones within a bandwidth of about 230 Hertz. The computer soundcard generates the tones and sends them to radio as an audio signal. The computer serial port supplies the “key to transmit” signal. Your radio’s signal level is adjusted for keydown operation. This is about 35 to 50 watts output for most transceivers. The received audio signal is fed into the soundcard and decoded as text by the computer. The hookup of the computer and radio is very simple. You can get all the parts in Radio Shack. This is the mode of the manned digital network known as TRR.