There is so much amazing activity these days surrounding satellite and software defined radio (SDR), but there are not many clear and current guides for those interested in creating receive only gateways to send satellite born APRS signals over the internet. Let's change that.
APRS & Satellites (and balloons, drones, etc)
Currently
there are three active satellite based digipeaters in low earth orbit. The International Space Station (ISS), PCsat NO-44, and SAT NO-84 all operate on 145.825 MHz.
There is also a fourth APRS satellite named FalconSat-3 that was turned over from the United States Air Force in 2017 for amateur radio use, but is operated on 145.840 MHz and requires a little more work to use. There are other amateur digital mode satellites in the planning stages.
What is an iGateway?
An iGateway is nothing more than a radio receiver that is connected to the internet. Signals received by the antenna are passed from the radio over the internet. The iGateway is designed for digital or data signals and not voice however. Websites such as
findu.com and
aprs.fi are two examples are where the benefit of igateways can be shown and show APRS data.
There is also the Othernet (Formerly known as Outernet) project that sends information from its ground station back up towards different satellites that "datacast" to special receivers such as the Dreamcatcher. Properly addressed APRS messages are in turn broadcast over this separate satellite network. This is not the same as an iGateway, but does add some other unique potential. For an amateur to route a message with APRS through one of the mentioned satellites earlier, one must use the path of "OUTNET" instead of "ARISS".
General users of APRS for ground based modes typically leave the path as WIDE1-1 or WIDE2-1, but those interested in satellite communications must use the alternatives listed since a satellite works differently from a propagation perspective to ground based or even low altitude aircraft or balloons.
How To: SDR & Raspberry Pi iGateway
To create an iGateway you will require:
- Raspberry Pi Computer or other similar device
- Antenna capable of overhead reception
- Various cables and stuff for your installation
There are way too many variables on antennas and cabling specific to every installation so we will keep this brief and skip that part. The shortest run of coaxial cable from antenna to radio is needed. The highest and clearest view towards the horizon in as many directions as possible is required for optimal reception when considering setting up a iGateway.
The satellites we will be monitoring pass over most locations about 3-5 times every day for just a few moments, so it's possible a APRS capable satellite will pass over once every 60-90 minutes.
Lets setup the software bits and bobs....
The main goal of this article is to only share the steps for configuring software to get a SDR dongle working with a Raspberry Pi. These steps can also work for those looking for alternate uses for SDR based hardware such as the now out of date L-band focused Dreamcatcher v 2.03 boards that were replaced with the newer Ku-band Dreamcatcher v3 and likely could be used too.
The real magic here is the software and how it will all work together.
First step, is get a working operating system on your device of choice such as the Raspberry Pi or Dreamcatcher v2.03. Most of these instructions will work for other linux based computers but is not the focus of this article.
Please run sudo apt-get update and sudo apt-get upgrade first to ensure your operating system is current and has most all of the popular packages installed for general use before continuing.
Second step, involves setup of Dire Wolf which translates sound to packet decoding. Run the following on your device to install it.
sudo apt-get install libasound2-dev
git clone https://github.com/wb2osz/direwolf
cd direwolf
make
sudo make install
make install-conf
Next, you need to configure the operating system to take virtual audio from an inexpensive SDR dongle and pass it to direwolf. Go ahead and plug in your SDR dongle to your raspberry pi. If you are using a Dreamcatcher, there is no need since the SDR is part of the board already!
sudo apt-get install cmake build-essential libusb-1.0-0-dev
cd
git clone git://git.osmocom.org/rtl-sdr-git
cd rtl-sdr
mkdir build
cd build
cmake ../ -DINSTALL-UDEV_RULES=ON -DDETACH+KERNAL_DRIVER=ON
make
sudo make install
sudo ldconfig
sudo reboot
Let's pause for a moment and test the SDR to make sure its recognized.
run "rtl_test" and ensure you get a status update like this before continuing. This shows that the SDR is being recognized by your Raspberry Pi, Dreamcatcher 2.03 or other single board linux computer.
Now we need to configure Dire Wolf and the best way to do that is copy some of the great work that Keith G6NHU has compiled. Head on over to his interesting site here:
http://qso365.co.uk/2017/02/a-guide-to-setting-up-an-aprs-receive-only-igate-using-a-raspberry-pi-and-an-rtl-sdr-dongle/
The only basic change you need to make is to select the correct frequency. In the United States much of the APRS activity is on 144.390 MHz, but since we are interested in satellite based APRS, change it to 145.825 MHz instead.
What did you say about balloons?
Perhaps you may tire of the same general activity on APRS terrestrial activity or even what may be bouncing off a satellite. The next logical thing to look into would be tracking a balloon of some sort.
Taner DB1NTO has a new product out to cater to people looking to track something that can only carry a very light weight device. He calls it
PicoAPRS Lite and should open up lots of possibilities to experiment with alongside perhaps with a portable version of an iGateway connected via cellular hotspot.
If anyone in the Hudson Valley is interested in experimenting with tracking objects other than a house which does not move much, or a car, lets start talking.
The STEM (31630) DMR talk group seems a logical spot as well as the AMSAT (98006) talk group, so lets make something happen here when spring time arrives!
