IRLP What is it?
IRLP
(Internet Radio Linking Project) is a type or method of communications
using Amateur radio frequencys (usually UHF or VHF) and a computer connected to the
Internet via a high speed connection. With this mode of operations you can connect and
communicate with other amateurs stations in other parts of the world.
A little history!
It was developed by David Cameron, VE7LTD of Vancouver BC. In 1997 he tried using Windows
based Voice over IP software. But the Windows linking software was unreliable and was
unsecure from hacker access. So in 1998, David switched to Linux software, which allows
an instant and secure link between licensed repeaters all around the world. We first
learned about this type of communications in the spring of 2002 when Earl WB7RES was in
the Seattle area and heard a QSO between Seattle and Hawaii over a VHF repeater. We were
able to discover how this type of operation was accomplished and we were successful in
installing the equipment and making it work.
How Does It Work?
The IRLP software uses audio from the receiver, feeding it into the sound card line in
port. There it is converted into digital data, like the format used by Long Distance
telephone service. The Linux PC converts this data into digital packets, which are
assigned the IP addresses of the node that you are communicating with. These packets
flow through the Internet to the destination PC where they are decoded, sent to the
sound card and out to the transmitter of the link radio which transmits the audio over
a local repeater or a simplex frequency. The transmitter is keyed when the TCP/IP packets
arrive. When the digital data stops, the link radio automatically unkeys and the process
reverses. The audio processing technology in IRLP is a freeware application called
“Speak Freely”. Speak Freely produces Voice-Over-IP (VoIP) audio streaming and is like
other VoIP software with one major difference - It runs under Linux not Windows. Linux
was chosen for the IRLP system as it allows the best in reliability, programmability,
efficiency, and functionality. The radio is controlled by a small logic board, which
connects to the parallel port of the node computer. This board detects DTMF tones used
for controls, detects when the link receiver is active, and sends the PTT signals to the
link radio. The DTMF codes controlled a program that reads the DTMF tones and are used to
activate various parts of the software. These codes are used to enable/disable linking,
open/close links and set identifiers. Every site has the ability to connect directly to
any site, either using a direct connection or using a reflector. Each node on the IRLP
network is assigned an ID code and a central server keeps track of the IP addresses in
use by all nodes.
IRLP Node Requirements
To set up an IRLP node you need:
1. A full time high speed Internet connection – DSL or Cable.
2. A dedicated Linux computer – a 486 DX100 or better is required.
3. The IRLP custom software/hardware.
4. A link radio or direct connection to a repeater.
5. The ability to mute all repeater ID’s, courtesy tones or DTMF control tones from
passing through the Internet.
How to use the IRLP Network!
Once you get the equipment running, you can connect to another node by dialing a 4-digit
code. This will cause a connect to the node and you will hear its callsign and location.
If the node is in use , you will receive a message telling you that the node is currently
in use. IRLP is subject to some audio delays which are caused by the amount of time it takes
for various equipment to switch from transmit to receive mode so you must remember to slow
down and be patient. When you complete a QSO, give your call and dial the OFF code.
What is a Node and a Reflector?
You have heard the terms node and reflector used several times. A node is one station
consisting of a radio and Linux based PC running the communications software to connect
via the Internet. A Reflector is a computer with very wide bandwidth connection that
allows multiple nodes to be linked together at the same time. The amount of bandwidth
required for a reflector is directly related to the number of connected nodes. A
reflector may have a number of nodes from around the world connected so any conversation
that occurs on one is heard by all connected stations. To simplify it, a node to node
connection is like making a party to party phone call and a reflector is like making a
conference call where several people are on line.
In summary!
By listening to IRLP you will witness a worldwide wireless network using an open protocol
to interconnect other amateur stations. This new technology is a tremendous asset to bring
new young blood into our hobby. As we all know there have been challenges to entice new
members into our hobby. Now with a HT they can talk with friends across town or around the
world. Where else can you talk to stations in England, Japan, Holland, or Australia without
fighting QRM, QSB and heterodynes which detract from the contact. With IRLP the audio is crisp
and clear so some very interesting conversations take place every day around the world.
