Demodulating the Outernet signal with leandvb and an RTL-SDR

Leandvb is command line based lightweight DVB-S decoder designed for receiving Digital Amateur TV, including signals like HamTV from the International Space Station. The RTL-SDR can be used together with leandvb and it turns out that leandvb can also be used to decode the Outernet signal. If you were unaware, Outernet is a free L-band based satellite service that provides content such as news, weather data, APRS repeats and more. Currently you can get about 20MB of data a day. Outernet receivers are also all based around the RTL-SDR, allowing for very cheap receivers to be built. At the moment you’ll need a C.H.I.P or their specialized Dreamcatcher hardware to run their special Skylark OS with software decoder, but a general Armbian decoder is in the works.

Alternatively leandvb can be used, and over on their website the folks behind the leandvb software have uploaded a tutorial showing how to use leandvb to decode Outernet. Thanks to some reverse engineering attempts by Daniel Estévez, it was discovered that the Outernet modulation is very similar to DVB-S so the standard decoder can be used with some custom flags. Leandvb only outputs raw frames, not decoded data. They haven’t tested it, but it may be possible to feed the frames into Daniel Estevez’s free-outernet project for obtaining the final files.

During the testing they also discovered some interesting notes about the E4000 and R820T RTL-SDRs. For example by patching the R820T2 drivers to add some additional VGA gain they were able to make the R820T2 chips more sensitive at the Outernet frequency compared to the E4000 chip by bringing the signal further out of the quantization noise. They also tested a 60cm dish vs a patch antenna and found that the dish works significantly better.

Patch vs Dish Antenna for Outernet
Patch vs Dish Antenna for Outernet

6 comments

  1. RTLNUT

    So anybodies know if I jack in to the old DISH Network sat dish on the house if that would work?
    It’s already pointed at where most geostationary satellites are and is almost big enough (I don’t know how accurate this stuff has to be).
    Should be worth a try at least.

      • Mick

        You can’t use a dual band LNB as noted in the link above. Outernet used to be on the Ku band, but it’s now on L band. Most folks have to roll their own feedpoint, as L band LNB’s are rare. One of the easiest ways to feed a dish is with a PCB Log Periodic antenna. Google “Kent Electronics” and look at the 850 – 6500 MHz antenna for an example.

        • Luigi

          good idea to use a log periodic to feed a dish. in the case of outernet and other innmarsat signals, should we care about vertical / horizontal polarization? does it matter when the signal is reflected by a dish?

  2. Luigi

    holy crap! it’s nothing new about the VGA gain in for R820T tuner, I submitted a patch to the mailing list to add indipendent gain settings like those exposed in airspy and the patch never get attention. it seems that the core developers prefer to keep the codebase stable and not add new features…. it’s a real pity…

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