This is from a previous post of mine (as this question comes up a lot):
To host a feed you will need:
1) A scanner with its own antenna
2) Computer with sound card (that allows audio/mike input) -
Note about a computer: It is preferable to have a dedicated PC/laptop but this is not necessary - the nice thing about a dedicated computer that hosts the feed is that what work you do on your primary computer (games, heavy graphics or video rendering) does not affect the feed - you can reboot and reload software all day long and it won't affect the feed. Another nice feature of having a laptop handle the feed is that there is a built-in battery that will keep the laptop up during nuisance power outages and significantly reduce the chance for a corrupted OS (due to the computer going off unexpectedly). I use an old Dell Latitude C500 (500 Mhz, 512 Mb RAM) laptop from about the year 2000 or so to provide the SYR feed.
If you don't have a second PC/laptop then it should not be a show-stopper but good feeds that keep listeners have high up-times.
3) An always-on Internet connection - DSL, FiOS, Cable, etc. - Obviously the PC hosting the feed needs to be connected to the Internet.
4) A simple audio cable that connects the scanner's external speaker/audio-out to the PC/laptop's sound card or mike input.
5) Free software installed called OddATC that Dave (the site founder) will provide that is very easy to configure and set up to run. This software takes the audio input from the scanner, converts it to a digital stream, then sends it up to the LiveATC servers.
------- optional but significantly improves the feed -----------------
6) An outdoor j-pole or discone antenna.
7) a low-loss coax cable that connects the antenna to the scanner
------- really, really optional ----------------------------------
8 ) A UPS into which the scanner, computer, and cable modem or DSL router are plugged to keep the feed running through nuisance power-outages. This of course depends on the frequency of power outages in your area. In mine there are at least four or five per year.