The images below are of the new ( 1985 Mfg ) General Electric Master 2 repeater unit and the antenna connected. Please excuse my HF wire in front of the picture. Clicking any image brings up a full screen detailed image. A special thanks to W5ZIT for making it possible.

UPDATE 9-9-2012:

Node 3221 is now operating at 40w with a GE Master II repeater in simplex mode. This upgrade should provide significant coverage increases locally. The node will be connected to a reflector 24 hours. A special thanks is also required for the assistance from Craig, K1BDX and Dave, KL7M for setup, configuration and continuing maintenance on my node software and hardware.

The IRLP uses a Voice-Over-IP (VoIP) streaming software called Speak Freely. Speak Freely is very similar to
other VoIP software packages (such as Microsoft NetMeeting and VocalTec iPhone) with one difference... It runs under
Linux. Linux is the operating system of choice for the IRLP system as it allows the best in reliability, programmability,
efficiency, and functionality. Most older IRLP nodes use Linux RedHat 7.3 or RedHat 9 as they are very stable releases
and run very smooth on any P1 or better computer.  Effective March 2007 IRLP started shipping an open sourced CentOS
version of Linux.  This release provides greatly improved operation with more support for audio cards. 

The concept of IRLP's use of VoIP is as follows:

   1.   Sample the audio using an analog to digital (A/D) converter. The A/D converter used by IRLP is the input 
        source of a standard PC sound card. This creates a continuous mono 16-bit digital stream of raw audio at 
        8000Hz (120000 bps).

   2.   Compress the audio by downsampling the stream and using an 4-bit ADPCM algorithm to reduce the size of the
        stream by a factor of four (32000 bps)
  
   3.   Split the sample into small chucks (or packets).
   
   4.   Transmit the packets to the remote host using a User Datagram Protocol (UDP) stream. UDP does NOT confirm
        the reception of packets, so it uses a "fire and forget" method.
   
   5.   Receive the packets on the remote host.
   
   6.   Join the split packets back into a 4-bit ADPCM stream.
   
   7.   Uncompress the ADPCM stream back into an 16-bit raw stream of audio.

   8.   Play the raw audio stream through a digital to analog (D/A) converter (the output device of your sound card).
        The control software controls the stream using carrier operated squelch (COS) or continuous tone coded
        subaudible squelch signals (CTCSS) to start and stop the stream. When COS is present, the computer detects 
        it through the IRLP interface board. The PTT is controlled by the buffer which joins the split packets back 
        into the audio stream. The IRLP interface board receives a "transmit" signal from the computer while there 
        are packets in the buffer, and a "unkey" command when the buffer is empty. The user interfaces to the IRLP 
        computer using DTMF signals sent over the radio. DTMF sequences are owner programmable, and can accomplish 
        almost any function imaginable. The DTMF signals are detected on the IRLP interface board and sent directly
        to the computer in binary, where they are converted into numbers. A DTMF software program which I wrote then
        runs commands on the computer depending on the code entered. These commands are what start and stop Speak
        Freely, basically establishing and breaking the link.

David Cameron
IRLP Designer
VE7LTD

Weather you are using Echolink or IRLP, quick-keying is verboten and will prevent remote operators from joining the conversation since the remote user will never be able to key up the radio to participate. Not only is quick keying annoying, it's also bad ham radio etiquette because it prevents anyone who may be monitoring from asking for permission to join the QSO and prevents any emergency traffic. This is the case for ANY repeater regardless of it's connection or lack thereof to a VOIP system. Please do not quick-key during repeater use. Let your local repeater's courtesy tone beep if it's equipped, close it's squelch, wait 2-3 seconds and then transmit. Let's all remember this is NOT Citizens Band Radio.

Another thing to remember is, most IRLP/Echolink systems are controlled with DTMF tones. This means you need to identify yourself BEFORE you send DTMF tones. Most Echolink repeaters will use a PREFIX for connecting to nodes such as the "C" or "A" button on your DTMF keypad. Look at your radio and you will see if so equipped, the A B C D and * # keys. These are all used in some way by repeater owners to tell the repeater software what it's doing and what system it needs to connect to. My system uses "C" then the Echolink node number to connect to the Echolink system and to other nodes. Otherwise direct entry of a 4 digit number such as "3333" will connect directly to that node number with the IRLP portion of the repeater.

Some systems, such as mine are SIMPLEX repeater systems. This means input and output (147.515) is the only frequency used. This also means, you may not hear a local user who may be operating with a low power handheld radio. It may seem like the station you hear ( via ECHOLINK ) is talking to him or herself. This is not the case. You simply can not hear the local user talking into the simplex repeater and can only hear the repeater transmitting the audio from the remote user where the Echolink node is connected. Before using a system like this one, simply wait 2-3 minutes before checking the system's connect status or attempting DTMF tones so you don't interrupt someone else who is using the system locally.

The computer shown below is an older Celeron 500mhz with 500MB of ram. The computer is plenty fast enough to run the CENTOS Unix operating system since all it does is run the IRLP/Echolink node software. In the third photo you will see the IRLP board which is not actually plugged into any of the PCI slots on the motherboard. It simply sits in a rear port to allow cables to connect. The parallel port cable goes from the back of the IRLP board and the computer. The audio from the computer sound card and radio is fed into the rear of the IRLP board also. Also required is an internet DSL or Cable Modem speed connection or better.

The IRLP radio below, a Motorola GM300 was donated by W2CEA. The box it's sitting on is my APRS TNC. Behind the radio itself is a standard high speed fan which blows air on the rear radio heat sink continuously to help prevent overheating by any long-winded QSO's. A special programming unit which steps the voltage down to program the radio via computer is used along with Motorola's programming software easily found on the internet. Any GM300 radio purchased is set on the public safety bands since these radios were designed for police and fire vehicles. Programming is required and you must know how to do it or you can damage the radio with too much voltage.