Sound Card Digital Radio Transmissions
We can send text and pictures over the radio by interfacing the radio speaker and microphone with a computer sound card. The information we wish to transmit is translated by software into patterns of audio tones which are transmitted within an audio bandwidth of up to 2 kHz within the normal pass band of a voice radio. At the receiving end software filters audio to the bandwidth of the selected mode and then decodes the text or image which can then be saved for printing, transferred to a flash drive, or put in an e-mail. It is basic connectivity outside commercial infrastructure.
Equipment can be as simple as acoustical coupling which is merely holding on radio mic to the computer speaker and the computer mic to the radio speaker or sandwiched in a set of headphones. The MT63 mode works very well for this. For other modes, you should use an interface to match the audio levels between radio and computer.
Why Use Digital Modes ?
When you need to transfer a written message quickly and accurately it beats using voice hands down. Digital radio traffic is also a bit more secure than voice from casual scanner listeners.
Text copy can be perfect under signal conditions that render voice completely unintelligible. The operator can select the appropriate mode for the band conditions at the time.
How do you recognize the different modes on the air? Sights and Sounds