Build your own echolink node using the raspberry pi for 100 euro.

Small unix devices like the raspberry pi, beaglebone, pogoplug and others are proving to be very usefull tools for all kind of ham related applications. They have been used in project involving D-STAR, rig-control and wspr server, for APRS node and other.

This project looks at another aspect of amateur radio: echolink.
The aim of this article is to describe how to create a complete echolink linknode using raspberry pi; complete for around 100 euro. The goal is to provide a platform to allow people to get their first experience with the raspberry pi, with interfacing computers and radios and with setting up ham infrastructure.

 

Overview

 

The hardware components needed for this project are:

  1. A raspberry pi + power + case + SD card
  2. A USB audio-fob
  3. (optionally) a USB-to-serial adapter
  4. A “digital modes” interface board (either self build or commercial)
  5. A handheld radio + (by preference) an external power-supply
  6. An external antenna

This project aims at using as much as possible homebrew equipement and off-the-shelf components.

In addition to the hardware elements, the following software and services are also needed to complete the setup:

  1. An internet connection for echolink access.
  2. The open source software package “thelinkbox”
After completion, the project will look like this:
 
(Raspberry pi powesupply and external antenna not shown)

Step 1: Preinstallation: registering on the echolink network

The goal of this project is to set up an echolink node. For this, a password is needed to register and authentificate the node on the echolink network.

The administative process to register on the echolink network and to obtain a password are described in the FAQ on the echolink website.
Do note that for registering on the echolink network you need the echolink application for windows (or for i386 linux users, the windows echolink application running under wine). This can not be done on the raspberry pi.

Step 2: Installation and configuration of the raspberry pi and the TheLinkBox software.

The installation starts from a freshly installed Raspberry pi using the standard “raspbian weezy” debian linux that can be found on the raspberry pi “download” webpage. How to do a basic setup of a raspberry pi can be found on a number of websites on the net: on youtube, instructables and Simon The Pi Man and other sites.

Do note that one of the steps in this process is a complete upgrade of the raspberry pi to all the latest software. Be warned that this step can -depending on the speed of the SD card- take anywhere between 1 and 3 hours!
It would be a good idea to do this step just after requesting your password to join the echolink network. By the time you receive your password, the upgrade of your pi may be finished. :-)
After the basic installation, additional steps are needed:

  • To configure the raspberry pi to access the USB audio dongle via the linux “Open Sound System” architecture
  • To download, compile and install the “thelinkbox” appplication.
  • To configure thelinkbox for your particular setup.

These steps are explained in the howto install thelinkbox on raspberry pi document.

 

 

Step 3: Hardware setup.

 

As mentioned in the beginning of this article, the number of components needed for this project is very limited. Basically, it contains 4 elements: a raspberry pi, a USB audio adapter, a interface board and a transceiver.
It is of course possible to add more components: external power supply, external antenna’s, a more professional interface-board containing a serial port interface, …

Two example configurations are described  in this blog:

  • Raspberry pi + handheld radio; using a GPIO-port of the Pi to control  the PTT of the radio.
    This setup uses the least compoent and is therefor the cheapest.
  • Raspberry pi + handheld radio + USB-to-serial adapter, using the usb-to-serial adapter to control the PTT of the radio.
    This setup is usefull as quite a number of computer-radio interface boards (homebrew and commercial) use the serial port control-signals to control the PTT of the tranceiver.

 

Interface board

:

To connect the raspberry pi to a radio, an interface board is needed. This circuit acts as insolation between the two devices.

These interface-board can be bought as commercial product (e.g. the signalink USB) they can easily be made as a homebrew project (see project of G4ILO, K0KN or 9W2WOC)

 

In this blog, I use the very basic interface board; originally created by VA3UV for the FreeStar project.

 

 

 

External Antenna:

Especially when using a handheld radio and a homebrew interface board, interference of RF signals into the interface circuit can be a major issue.

So it is usually not a good idea to have the antenna of the transmittor of the echolink node located to close to the node and -if possible- use an external antenna on that radio.

A very cleap option for a homebrew external antenna for 145 Mhz is a slim jim antenna as described on the hamuniverse website. It is just made out of wire and a PVC pipe. Using such an antenna at 5 to 10 meters away from the radio is usually sufficient to eliminate RF interface from the transmittor into the interfacing circuit board.

 

 

Using the echolink linknode:

 Once the echolink linknode has been set up and configured, it can be controlled methodes: the tlbcmd application or via DTMF.
tlbcmd is an application that -as its name implies- can be used to send commands to the tlb daemon process. Examples of tasks that can be triggered by tlbcmd are:
  • query information about connected users or links to remote repeaters, links or conferences
  • connect and disconnect thelinkbox from remote echolink nodes
  • reconfigure thelinkbox on the fly: activate / disactivate RF modules, activate / deactivate APRS messages, …
  • issue spoken-messages operations
  • shut down thelinkbox
The configuration for DTMF is configured in the file /home/pi/tlb.cmds It contains the rules to translate  DTMF codes into commands for thelinkbox. Some examples are:
  • Sending * is equivalent to “disconnect last”
  • Sending any 4 to 6 digit code is translated to a connect request to the echolink node with that number.

Check out that configuration file for more information about DTMF commands.

 

 

Applications a the echolink linknode:

So, what can a echolink linknode and the “thelinkbox” application be used for?

 

A number of practicle applications for PERSONAL USE come to mind:

  1. For people who live in a area where no repeaters are available, a linknode is a “repeater light” setup that require minimal setup.
    A linknode can be set up for only personal use or as a community service in general.
  2. As a linknode can be made to permenantly link to a repeater; it can be seen as an extension of an existing repeater.
    For people living (say) 5 to 10 kilometer away from a local repeater, a linknode allow them to work the repeater, locally via the linknode instead of having to bridge to distance to the repeater. This allows the use of handheld radios at low-power; as it not necessairy anymore to transmit at full power to reach the (far away) repeater.Connecting the linknode with the repeater van be done via echolink over the internet or via a direct wifi link between the two sites (e.g. by using 5 Ghz wifi links).
  3. An echolink linknode can not only access remote repeaters or other linknodes, but it can also be used to take part in QSOs using one of the many echolink conferences.Having a “personal” linknode is especially interested if somebody is particular interested in the more specialised conference or conferences using foreign languages, something that would probably not be very appropiate to be done on a repeater serving a complete city.Some examples of echolink conferences are:
    *IRELAND*, *BONJOUR* are two conference used by respectively english-speaking and french-speaking hams from all over the world. Simular conferences exist for other languages too.
    *DODROPIN*: a conference server mainly used for nets, with net almost every day.
    *WORLD*: a conference that bridges echolink stations and repeaters on the IRLP (Internet Repeater Linking Project) network.
    N1DOT-R: not a conference, but a repeater that acts as bridge between echolink and the allstar network. This repeater is linked to both a IRLP conference and a D-STAR XRF reflector. It is also the place to find people very much interested in ham voip systems.
Appart from the personal use, setting up a echolink node is also usefull for a number of other applications:
  • Setting up an echolink node is the first step to learn more about setting up ham infrastructure equipement.
    The two setups described in this article has been on purpose kept to a minimum. It is mainly a setup designed for personal use. Extending this setup for a more permanent echolink linknode or repeater setup does require additional steps the setup more robust.
    Issues that come into play in these senarios are heartbeat signals to verify the state of the echolink node software, remote-access systems to intervene as quick as possble in case of problems, hardware COS (carrier sence) for better detect the presence of signal, hardware DTMF decoders, interconnect to other ham voip-systems like IRLP or allstar and others.
  • In an emergency communication setup, “thelinkbox” can be used to interconnect two or more areas: hams using handheld radios in one area can -using a thelinkbox setup- communicate with people in another region.If the connection between these two sites is done via wireless IP links (e.g. 5 Ghz wifi links) the whole setup can be done without any need for external resources.
    The combination of raspberry pi + handheld radio + wifi link in this setup is especially interesting because it it’s small size and small power-requirement; which allow this kind of nodes to operate completely on battery-power.
  • Althou the setup described above uses only one single radio module, the thelinkbox software is able to control multiple radios in one repeater. This does not only allows features like crossband repeaters, but also setting repeaters / linknodes at less used bands (like 29 Mhz, the 6 meter band, the 70 Mhz 4-meter band or 220 Mhz 1.5 meter band).
  • Thelinkbox can also be used for your own private or public conference server. This opens posibilities to use it to virtually interconnect a number of different repeaters in a certain region, all under your own control and without any external resources.
  • The linkbox provides an event-API that allows you  to write application on-top of it to add features. In additional to that, the sourcecode of thelinkbox itself is available as open-source.
    This offers the ability to learn more how to extend and adapt the system for your own needs, for your specific hardware or simply to learn what a repeater really is made of.
    The extension of the thelinkbox code to support the GPIO pins of the raspberry pi or other small embedded linux devices is one example of such an extension.

 

As shown, this project has a lot of possibilities. It does not require that much hardware and -if for some reason you do not like this project- everything can be reused for other projects.

It is a first step to getting to know the raspberry pi, learn more about setting up ham infrastructure and does provide a number of very practicle applications.I hope some of you might find this usefull.73
Kristoff – ON1ARF

(version 20130511).