1 Introduction

The IRLP Node 6214 operated by AREG and maintained by Adrian VK5ZSN. The IRLP Node allows the AREG repeater VK5RSB to be connected to a large number of other voice repeaters across the world.

The resource requirements of IRLP are low, and older computer equipment can be utilised to run the Node.

For detailed information please visit the IRLP web site, www.irlp.net

2 IRLP Acceptable Use Policy

The IRLP node is free to use by all licensed Amateur Radio operators. The computer hardware, Internet bandwidth, mains power and repeater access are all provided at no charge by AREG members and other interested amateurs.

The only thing we ask in return is the users of IRLP Node 6214 abide by the AREG IRLP acceptable use policy.

Identify before sending DTMF commands.
If VK5RSB repeater is busy, ask before dialling a remote node.
Avoid using IRLP during drive times, 7am - 9am and 5pm - 7pm
Once finished using the IRLP Node, send a disconnect command (73)
Leave around 2 to 3 seconds between overs (allows for delay and lets other join in)

AREG wishes you enjoy using IRLP Node 6214.

3 IRLP Node 6214 DTMF Commands

The DTMF commands are used to control the IRLP node. Some commands are only supported by IRLP Node 6214. In addition to the IRLP command is an access code which proceeds the IRLP Command

Due to non licence operators ( Pirates ) an access command was added to IRLP node 6214. To activate the IRLP function, you must first dial the access command, then followed by the IRLP function command. The IRLP access command will variy from 3 to 8 digits, the access command is usually updated on a regular basis.

Function	IRLP Access Command	DTMF Command
Current Status of IRLP Node 6214	n	0
Disconnect an IRLP connection	n	73
Current Time in Adelaide	n	11
Dial a remote IRLP Node	n	xxxx

To apply for the access command send an email to

Don't forget to include you contact details, call sign in the email, please be patient for the reply, but we will get back to you.!!

4 Installation of Node

The IRLP node was first installed at Adrian VK5ZSN QTH. It was set up using an spare computer using a Version 3 IRLP board. The node was set up as an experiment to see what all this hype was about with VOIP (Voice Over Internet Protocol). Refer to the IRLP History page for more details on the story behind IRLP Node 6214.

4.2 Relocation of IRLP Node

The IRLP Node was relocated back to Adrian VK5ZSN while Peter VK5TZX house gets renovated. Since the IRLP Node 6214 now runs a low power VIA C3 Mini ITX computer it is not much of a problem to have an extra computer running all the time.

As a new member of the family was getting bigger, and wanted here own bedroom, the IRLP node had to be moved again. But while it was here it got an upgrade to a low power computer using a VIA C3 board, which reduced the power consumption of the node down to 33watts. Further improvements are possible but this would involve changing the IRLP computer PSU over to a more efficent power supply. This will probably happen when time permits. The IRLP node is now back at Adrain VK5ZSN's house.

4.1 Dedicated Repeater Link

As the IRLP node was first commissioned, a dedicated link was started being built to connect the IRLP node directly to the voice repeater.

The link radio equipment was modified and put into a couple of boxes. All that was left to do was wire it up. Then the age old problem happened, the members working on the project got too busy with work and other projects and the link is waiting to be finished. One day it will be I am sure.

Rear View of the IRLP Direct duplex link

4.3 IRLP Audio Interface Audio Shaping

The requirement of TIA/EIA 603 standard indicates that FM radio's will use Pre-emphasis and De-emphasis to improve the signal to noise at high audio frequencies.

The requirement to use the AREG Standard interface that uses a flat audio system, with no Pre-emphasis and De-emphasis being employed in the radio. As Pre-emphasis and De-emphasis allready applied in the user radio. The IRLP Audio Interface would need would to include Pre-emphasis and De-emphasis circuits. An extract of the circuit and the expected band plass plot are shown below.

De - emphasis Circuit IRLP Audio Interface

Shelving Amplifier Low Pass Design

As this circuit was tested on the IRLP node a small change was need in the orginal design, but a measured audio response corner frequency was around 300 Hz.

Pre - emphasis Circuits IRLP Audio Interface

Inverting Shelving Amplifier High Pass Design

As you can see, the plots of the two amplifiers are opposite to each other and provide a good 50uS de-emphasis and pre-emphasis. However after some testing, the orginal frequency response was found to be incorrect, and not enough boost was provided by the filter at frequencies above 300Hz.

Other aspects of the design also included electrical isolation between the computer and the radio of the IRLP Audio Interface. This was achieved by using opto couples and 600ohm to 600ohm transformers. The radio side of the IRLP Audio Interface is powered by the radio power supply, where as the computer side of the IRLP interface is powered by the computer power supply.

In additon to the pre-emphasis and de-emphasis circuits, a band pass filter was added to the system, this would allow the removal of CTCSS (PL) tones from going down the IRLP link and any very low frequency audio from the link being transmitted by the radio.

The IRLP Audio interface board, that would allow the IRLP audio and control lines to be converted to the AREG standard interface. With some operational amplifiers and the balanced line receivers / transmitters. The interface to the AREG 15pin standard interface was achived. Also included on the board are transformers and opto couplers that provide electrical isolation between the IRLP Node computer sound card and the radio. This assists with stoping computer hash from getting into the audio section of the radio. In addition the balanced interface between the IRLP Audio Interface and the radio also assists with removal of noise from the audio system.

In short, the IRLP system sounds fantastic, if you don't beleive me, dial Node 6214.

Design has been updated in late 2009, to allow a straight through cable between the IRLP Audio interface and the IRLP IO Intervace Rev 3.0.

IRLP_Audio_Interface_Schematic_Version_1.1.pdf	AREG IRLP Audio Interface Schematic for Version 1.1
IRLP_Audio_Interface_PCB_Documentation_Version_1.1.pdf	AREG IRLP Audio Interface PCB Layout for Version 0.4, also shown below

5 Update & Repair of IRLP Node

It was time to update the old IRLP node computer to a new one. A number of attempts were conducted to try to get the IRLP software running of the VIA. In the end we just had to wait for the developers to get up to speed with the technology, and create a system that would work with the newer versions of sound cards. . Once that happend, it was an easy task to move to the new machine.

The IRLP Audio Interface had also had a revision, and now with some commercially made PCB, version 0.4 shown below mounted to bottom of the node computer.

IRLP Audio Inteface Version 0.4 installed in bottom of node computer

As most IBM compatible personal computers have at least some space inside the case. The IRLP interface can be mounted inside the case and wired to the back panel of the computer. One day when I get time I may get around to designing a surface mount PCB for this board. As it is a lot easier to make and not drill as many holes.

The following photo shows the IRLP interface PCB installed in side IRLP Node 6214 computer.

The power cable and the AREG Standard Interface cable run from the right hand side of the IRLP interface PCB to the rear of the computer.

The power cable has a 2 pin Ultilux male connector installed in the rear of the computer, a spare 12Volt DC feed from the radio power supply is plugged in. The 15 pin D type female is mounted close to the IRLP radio side DC power connector, for detail refer to the following picture.

The picture on the left shows the outside of the computer where as the picture on the right shows the inside of the computer.

The DTMF audio, SQL, PTT signals are normally feed into a Male 9 pin D type on the rear of the computer which connects to the IRLP 10 pin header. As the IRLP interface was being installed inside the computer. A new longer cable was manufactured using the same pin outs as the shorter cable and a direct connection between the 10 pin header on the IRLP Version 3.0 board to the IRLP Interface PCB.

The IRLP I/O Inteface will need to be modified if the DTMF led is to work on the IRLP Audio Interface, refer to IRLP I/O Interface Mod web page for details. Node was ready for connection to the linking radio / repeater.

5.1 IRLP Node Radio

The radio to be used for the link is a Motorola Syntrx. The radio required some modification to get it to work correctly on the required part of the 70cm spectrum.

The installation of a DX Interface PCB inside the Syntrx radio provides the AREG standard interface levels and control signals. The following picture shows detail on where the DX Interface was installed.

As the syntrx was a link type of radio, it came with a 15 pin D type female connector all ready installed on the front. A simple modification to the radio involving two 240 ohm resistors in parallel, turns on the radio with requiring a microphone plugged in.

5.1.1 Alignment of the DX Interface PCB

The DX interface PCB has four pot on the board. three volume controls on the board.

The radio alignment can take a bit of fiddling depending on what type of test equipment you can use.

The first step is to set up the receiver maximum audio level. Using a RF signal generator or service monitor ( or other equipment as required) generate a 5KHz deviated RF signal on the radio Rx frequency and modulate with a 1KHz tone.

Using suitable audio balanced line power meter (or dual channel oscilloscope) terminate the DX interface output into a 600 ohm load. The suitable audio blanced line power meter may have this function built in. Otherwise the dual channel oscilloscope and two 1K2 1% resistors in parallel will do the job.

Adjust VR1 so that the audio level is 0dBm, that is 1mW into 600 ohms. Once this is set you can adjust the frequency of the audio tone and variy it from 50 Hz to 4KHz. Adjust VR2 for best flatness across this frequency band. While adjusting VR2, you may need to re-adjust VR1 to ensure the audio power level at 1KHz is set at 0dBm.

Set up an balanced audio signal generator to generate a 0dBm signal terminated into 600ohms at 1KHz.

Once the audio signal is set up. Feed the audio signal into the TX audio port of the DX interface and make the radio Transmit. Using a RF deviation meter or service monitor measure the RF signal deviation.

Adjust VR3 so the RF signal has 5KHz of deviation. Then adjust the audio signal generator frequency and sweep the audio signal from 50Hz to 4KHz. Adjust VR4 for best flatness over the 50Hz to 4KHz frequency range.

The audio alignment of the radio is now complete. The maximum audio / deviation of the RF link radio has now been set up. Usually most audio will cause the radio to only deviate 3.5Khz. which equates to about -6dBm on the balanced audio system.

5.2 Alignment of the IRLP Interface PCB

The audio alignment of the IRLP node radio has all ready been done. This is required as you can either use the radio in circuit and measure deviation and generate a suitable signal, or you can use a suitable balanced line signal generator.

Set the audio level adjustment of the audio output from the sound card of the IRLP node to the middle of it's adjustment.

Configure the balanced audio power meter or dual channel oscilloscope to measure the IRLP Interface output level. The test wav has voice and a sine wave signal on it. The part to measure is the sine wave signal. Adjust VR1 so when the sine wave signal is being played by the IRLP node the measured output of the IRLP Interface is 0dBm.

This once again sets the maximum audio level of the system. While playing the audio test file you will notice the voice is around -6dBm in level with respect to the sine wave at 0dBm.

Set the audio level adjustment of the sound card for input audio to the middle of the adjustment range.

Using the IRLP Echo Reflector, and a balanced audio signal generator, input into the IRLP interface a 1KHz audio tone with a level of 0dBm.

Adjust VR2 so that the same level is played back by the node as is being input into it. It may take some stuffing around but you can get the node to play the same level back as is going into the node.

Once this is complete the audio level are set up on the node, the only thing left to do is adjust the DTMF audio level.

Using a DTMF tone generator on a radio tuned to the RX frequency of the link radio. Generate a 2K8 deviated RF signal and adjust the VR3 so the DTMF led lights on the IRLP I/O interface. With a lot of experimenting if the DTMF tone decoder starts to work at about 2K8 for the RF deviated signal, you will find that most people's DTMF will work fine. If you set the DTMF level too high, you can limit the head room you have available in the DTMF decoder.

By now you should have the IRLP interface and link radio all aligned. Happy playing with IRLP.