IRLP
The Official Site of the IRLP
The Internet Radio Linking Project, also called IRLP, is a project that links amateur radio stations around the world by using Voice over IP (VoIP). Each gateway consists of a dedicated computer running custom software that is connected to both a radio and the Internet. This arrangement forms what is known as an IRLP Node. Since all end users communicate using a radio as opposed to using a computer directly, IRLP has adopted the motto "Keeping the Radio in Amateur Radio".
Amateur radio (or ham) operators within range of a local node are able to use DTMF to initiate a node-to-node connection with any other available node in the world. Each node has a unique 4 digit node number in the range of 1000-8999. A real-time searchable list of all nodes worldwide (including their current status) is available anytime by viewing the IRLP Network at a Glance. As of April 2007, there are over 1,280 nodes across 7 continents.
Stations wishing to communicate with 3 or more nodes at the same time may accomplish this by connecting to what is called an IRLP Reflector. Most reflectors on the network have 10 channels (0-9) with channel 0 being the main channel. Each reflector has a unique 4 digit node number in the range of 9000-9999. The first 3 digits consist of the reflector number, while the fourth digit represents the channel number. As of April 2007, there are 20 operational reflectors (including Echo Reflector 9990, which digitally records and plays back your transmission for testing purposes). Since most reflectors have 10 channels, there are approximately 200 unique reflector channels available for use.
Operating System
Linux is the (OS) of choice for IRLP, as it allows the best in reliability, programmability, efficiency, and functionality. Most older IRLP nodes use the Red hat 7.3 or Red Hat 9 distribution, as they were very stable releases and ran very smoothly on any Pentium or better computer. In 2005, a custom version of Fedora Core 3 was introduced, followed by Fedora Core 5 in 2006. As of March 2007, IRLP no longer supports Red Hat and started shipping with the CentOS 4.4 distribution. This release provides greatly improved operation with more support for audio cards.
IRLP Hardware
An IRLP board is required to interface to the radio. Currently version 3.0 IRLP boards are available fully assembled and tested. Each board comes complete with all the cables between the board and computer parallel port (with sub-hoods) and terminates in a male DB-9 connector for interface into the radio. You will require a female DB-9 to interface your radio/repeater/controller and two mono or stereo 1/8" audio plugs to connect to your sound card. The audio circuitry (since it is specific to your hardware) is the owner's responsibility.
The IRLP board is a very simple circuit, the most difficult part being the DTMF decoder. The DTMF decoder is comprised of a MT8870 (or similar) DTMF decoder IC and HCF4081 (or similar) and-gate IC. Two chips are needed because the MT8870 has latched outputs, and the IRLP software looks for short pulses at the parallel port pins 10,12,13,15 in order to acknowledge a DTMF digit. MT8870 pin 15 provides a pulse when any valid DTMF digit is decoded, so this signal is used on one input of each gate on the HCF4081. The other gate input is from MT8870 pins 11,12,13,14. The output of the HCF4081 (pins 3,4,10,11) connect to the parallel port and provide the pulsed input that IRLP needs.
The IRLP software cannot decode the D digit. This is a system limitation of IRLP, so even the $200 factory IRLP boards suffer from this problem. DTMF digit D is logic level 0 on all 4 bits from the MT8870. Thus, the parallel port pins would all be at 0 volts, which IRLP regards as no DTMF digit present.
The IRLP board has no audio transformers or bypass capacitors whatsoever.
Version 3 IRLP board has been duplicated and can be built by anyone with a small amount of electronics experience