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If I get involved in digital communications do I need to buy a soundcard?

If so, why, what does it do?

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Most radios are analog, or use analog audio in and out, and the sound card is used to interface between a computer and these radios.

The computer running suitable software uses the sound card to implement a digital communications mode such as PSK31, RTTY, or AX25 Packet.

Most computers come with a sound card, which will be good enough to get you started. However, many prefer to use a second card (or a USB-attached external card and interface such as the Tigertronics Signalink) so that they can have both speakers/headphones and their radio attached at the same time. It also helps you to not transmit your computer's startup sound effect accidentally.

Many people also choose to place an audio isolation transformer to isolate the computer from the radio, so that RF or DC power won't accidentally burn the computer or radio. At this point you should also isolate any possible PTT keying line (serial port?) using an opto-isolator, unless you're using voice-activated keying (VOX) to automatically turn the transmitter on when there's audio coming out from the computer.

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    $\begingroup$ Also note that most computers have sound cards built in, and that they are "Good enough" for many tasks, like PSK31, RTTY, and AX.25. However, the higher end, more expensive audio cards that have higher sample rates can be useful in Software Defined Radio (SDR) applications that require wider frequency bandwidth, such as waterfall displays and the like. $\endgroup$ – KD7KUJ Oct 23 '13 at 3:15
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Some recent transceivers (IC-7100, IC-7200, IC-7410, IC-7600, IC-9100, TS-590, TS-990) include a "virtual soundcard", meaning that a simple USB connection between computer and transceiver creates a device that appears to the operating system as a soundcard that digital mode applications can use in the standard way. The USB connection also handles RX-TX switching via CAT commands.

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  • $\begingroup$ Very good to know. $\endgroup$ – user157 Oct 23 '13 at 17:06
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No, most computers have one already. Look for 3.5mm TRS sockets on the computer that you would normally use for audio; speakers, earphones, microphone, or line connectors.

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    $\begingroup$ Using a PC with one soundcard is a recipe for transmitting "Windows noises" over the air. $\endgroup$ – AA6YQ Oct 23 '13 at 4:39

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