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Using a Raspberry PI as a portable APRS box

The Raspberry PI is more than capable of running Polaric Server, specially the Raspberry PI 4. It has plenty of computing power for this task. Here I will give some tips how to use this machine as a portable, headless APRS Box.

This article is work in progress. Stay tuned and feel free to contribute...

Operating system

Raspbian Buster works very well. Use the light version (headless). You may have to connect it to a sceen and a keyboard to run raspi-confg and activate ssh logins. After this is done, use ssh to login. If your PC and the PI is on the same LAN, mDNS can be used to find the IP of the pi. If the hostname of the pi is 'raspberrypi' it can be connected like this.

ssh pi@raspberrypi.local

Wireless router

If the box is to be portable there may be different and changing ways to connect it to the internet, it possible at all. So we may want a wireless LAN to which we can connect clients (laptops, smartphones, etc). We may want to use the raspberry PI as a router that can connect it to the internet either via a ethernet cable or Wifi.

RaspAP is a solution that is fairly quick and easy to install. It comes with a web interface based on a responsive design, i.e. you can configure the router/LAN using a smartphone as well as a PC. There are however a couple of things to be aware of:

(1) RaspAP runs on LightHttpd, Polaric Server runs on Apache 2. It is possible to run more than one webserver but they must use different ports. I suggest to change the RaspAP http port to something else than 80. Edit /etc/lighthttpd/lighttpd.conf and change server.port setting. I suggest 8080. Don't use port 8081 since Polaric Server needs this.

(2) RaspAP configures NAT on all network interfaces, including lo (loopback), this can lead to trouble connecting to local services. This can be fixed by adding a iptables rule like this:

iptables -t nat -I POSTROUTING -d 127.0.0.0/8 -j ACCEPT

Radio

You may want to connect the box to a radio. It can be done in different ways. One idea is to use a soundcard-modem. Direwolf is a good choice. Note that the Raspberry PI doesn't have a proper sound interface so you will need to add a USB sound interface. We may use one of the cheap usb-sticks, e.g. Logilink UA0053 and use one of the GPIO pins as PTT (and maybe one as DCD indicator by connected it to a LED). You will need to make some circuitry for interfacing this to the radio (it may depend on the radio). You will need a transistor or a optocoupler for the PTT keying. The Direwolf documentation have some information on how to do it.

Alternatively there are USB sound interfaces speficically made for amateur radio. For example a Signalink box . It is easier to get up and running and robust but it is somewhat more expensive.

(circuit example and pictures may be added later).

Install and configure the Direwolf software. Polaric Server can connect to the 'KISSPORT' so remember to activate this and take note of the port number. If you want a igate, Polaric Server can provide this so you don't have to configure the Direwolf igate. Actually you have a choice. You shouldn't activate both at the same time.

Polaric Server

Follow the instructions here to install Polaric-aprsd and Polaric-webapp. To use the Direwolf radio interface, you should configure the radio channel as 'TCPKISS' type, set the hostname to localhost and port number to the same you configured the KISSPORT setting in Direwolf.

rpi-box.txt · Last modified: 2020/07/20 20:35 by la7eca
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