While the image is downloading, let’s take a brief tour of how the L-band service works.
The files that are datacast by Outernet are encoded, modulated, and sent to several Inmarsat satellites. These satellites transmit the radio waves in the L band frequency range. The waves are received by a radio on your receiver and then passed on to the software demodulator. The demodulator turns the analog signal into bits and then passes them onto the decoder, which extracts the file information from the data and reconstructs the files on local storage.
The software components involved in this process are:
- the demodulator (sdr100)
- the decoder (ondd)
- file indexer (FSAL)
- web-based UI (Librarian)
Despite all this software coming from a single vendor, they don’t come as a single package for the reasons of flexibility and so that various components can be replaced by others with same or similar functionality in future. Because of this, much of this guide is going to be about ensuring that these pieces of software work together.
Although these pieces of software are all part of the Outernet software eco-system, which is predominantly open-source, some of the executables are closed-source.
Virtually all of the software involved in this set-up is meant to be used as long-running background processes (a.k.a. daemons). Some of the programs already provide features that let them run as proper well-behaved daemons, while others do not. Where appropriate, we will use screen as a quick-and-dirty workaround (i.e., poor man’s daemonization) solution.