I have been asked this question a number of times. I will attempt to give a brief overview of how it works. If you have any further questions, please feel free to ask.

I am using two Radio Shack Pro 2052 Trunk Tracking scanners with RS232 (serial) output. The scanners are located in a tiny room in Tierrasanta each with Radio Shack loaded 800 MHz rubber duckie antennas. Reception is adequate, and may be possible to improve with better antennas.

These scanners are each connected to a sound card on a Pentium 4 PC with a 3.4 GHz processor and 1 GB of RAM located in San Diego, Ca. I am currently using the Fedora 3.0 operating system. The current system specs are much more than needed to run such a site, as my previous server was a Pentium II 500 MHz computer with less than 350 Mb of RAM. With both scanners running, the system load is approximately 0.17 and 96.7% of the processor in an idle state.

My home system uploads the trunked audio and meta-data to a remote computer which has much higher bandwidth than my home system which is running on a cable modem. The remote system (located in La Jolla) rebroadcasts the audio as well as serves the primary web page and forums. The remote system is a P4 1.8 GHz machine with 768 Mb of RAM. System load is about 0.87 and 85% idle.

Both the remote and local home systems are running icecast 2.2.0 and ices 2.0.1. Icecast 2.2.0 is the streaming audio server and ices 2.0.1 is the client which converts the scanner audio on the line inputs of the sound card into the ogg file format which is uploaded into the local server. The "local" server relays the data to the "remote" icecast server, which then relays it for broadcast over the internet.

Metadata is read in via RS232 on each scanner. Scanner 1 is directly connected to a serial port and Scanner 2 & 3 are connected through a USB port via a USB to serial adapter. The serial data is gathered as a Trunk ID, which is further converted via a hash to a Trunk ID and character string which describes the Trunk ID. The Trunk ID and its description are uploaded into the ices client as metadata strings, simultaneously with the audio portion of the stream. The aircraft scanner is similar, but rather than collecting a trunk id, a frequency is collected and then referenced via a hash to a physical airport description.

The metadata and scanner control programs are all written and programmed by me, via the PERL programming language. The web site, driven with behind the scene PERL scripts uses Macromedia Flash and other html "tricks" to show a real time status of the stream, the stream description and the number of connected listeners.

• If you are interested in what the back of the local server looks like, with all the audio cables, RS232 cables, and sound cards, please click here.
  
  
• If you would like to see what the scanners look like, please click on the following images: image #1 or image #2.