Aeronetworks sro - Airborne Linux

I would like to send video over a satellite modem, but these things are as slow as 1990s era dial-up modems.  HD video with the H.264 codec streams at 2 to 3 Mbps, so the amount of data must be reduced by a factor of ten or twenty for low speed satcom. RPi with Camera Instead of running at 30 fps, one should stream at 1 or 2 fps and  most off the shelf video encoder/decoder devices don't know how to do that, so I dug a Raspberry Pi v3 and a v1.2 camera out of my toy box, installed gstreamer and started tinkering on my Mac to gain some experience with the problem.    Of course one can do the exact same thing on a Linux laptop PC, but what would be the fun in that? With the gstreamer videorate plugin, one can change the frame rate to almost any value and cranking it down to 1 or 2 fps is no problem.  One could go down to a few frames per minute, but super slow streaming could cause a playback synchronization issue, because the player error handler ma...

I recently encountered a nice looking video encoder/decoder device by a Canadian company called Haivision , which seemed to be able to do exactly what we needed.  These devices use OpenEmbedded Linux to do video streaming, so that one can take an SDI camera and stream the video over ethernet with MPEG-2 TS and decode it again on the other end. Multicast Route Bug Unfortunately, we found a multicast configuration bug:  The unit lacks a multicast route. The multicast route is explained in the route man page:   route add -net 224.0.0.0 netmask 240.0.0.0 dev eth0 This is an obscure one documented so people know how to do it. This sets all of the class D (multicast) IP routes to go via "eth0". This is the correct normal configuration line with a multicasting kernel. It can be fixed easily if I could log in with SSH and add the route setup in /etc/rc.d/rc.local .   Chain Gang Software However, after some backing and forthing with their customer support,...

The Intel Page Table Bug and the Multithreading Bugs , have spurned many discussions and a lot of complicated hard work is going into mitigating it, but I am not convinced that the software mitigations are sufficient .  The problem will only really be solved once Intel fixes the bungle in their processor microcode (which is currently causing processor crashes causing the bungled Intel fixes to be withdrawn by Dell and HP), or make new silicon. Theo De Raadt seems to agree with me: "Solving these bugs requires new cpu microcode, a coding workaround, *AND* the disabling of SMT / Hyperthreading." The latest OpenBSD news on the mitigation of these bugs is here: http://www.undeadly.org/cgi?action=article;sid=20180824024934 and you should read this: http://www.undeadly.org/cgi?action=article;sid=20180815070400  I have written more than one assembler, linker and debugger when I was younger and computers were simpler.  I have found and fixed a bug in an Intel ...

This article was reprinted in OSCAR News, March 2018:  http://www.amsat-uk.org If you want to receive Satellite Weather Pictures , then you need a decent antenna, otherwise you will receive more noise than picture. For polar orbit satellites, one needs an antenna with a mushroom shaped radiation pattern .  It needs to have strong gain towards the horizon where the satellites are distant, less gain upwards where they are close and as little as possible downwards, which would be wasted and a source of noise.  Most satellites are spin stabilized and therefore the antenna also needs circular polarization, otherwise the received signal will flutter as the antennas rotate through nulls. The helical antenna, first proposed by Kraus in 1948, is the natural solution to circular polarized satellite communications.  It is a simple twisted wire - there seems to be nothing to it.  Various papers have been published on helix antennas, so the operation is pretty well ...

To receive Satellite Weather Pictures , you need a special antenna that will handle the rotating signal. Dimitris Papadeas at SatNOGS built a variety of 2 meter band helical antennas: https://community.libre.space/t/uhf-helical-v4-instructions-and-source/617 To see how well it works, I modeled his design with NEC2 using CocoaNEC on my Mac.  The radiation pattern looks cool.  With 12 dB gain, it would be good on a simple tracker or for permanent pointing at a Geo sat.  You cannot just point it up at the sky to catch a polar bird, since then a satellite would have to pass almost directly over head, which doesn't happen very often. 2 m Band Helical Antenna Pattern At this size, a crossed Yagi would be rather easier to build though. A helix is more suitable for the 70 cm band, where it will be much smaller and easier to support. CM Helix, SatNOGS, v4 CM Frequency: 434 MHz CM Wavelength: 691 mm CM c=299792458 m/s CM Radius = 110 mm CM Turns: 8 CM Circumference...

If you wish to make a standalone router, file server, or satellite weather station, then you need a little computer to make things happen.  At this time, the most popular embedded Linux machine is the Raspberry Pi .  It is a delightful little design - tiny and very useful. The default system is Raspbian , which is loosely based on Debian .  This is excellent.  Years ago, I tried a Beaglebone Black and it came with a cripple version of Angstrom Linux which I didn't like and the board is consequently lying somewhere in my junk box. The Raspbian system is aimed at clueless newbies and the ssh daemon is disabled by default.  To use it as an embedded server, without having to plug in a keyboard and screen, you need to add one line to a configuration file, before you plug the SD card into it.  Here is how to do all that. Get a Pi and a SD Card Image Get your RPi3 from here: https://www.sparkfun.com/products/13826 Download a Raspbian im...

There are about 3000 active communications and earth observation satellites flying over our heads at all times (plus about 2000 dead ones).  Many of the earth observation satellites broadcast useful data which anyone can receive, once you acquired the necessary equipment and know-how.  See this https://amsat-uk.org/   Clouds in the UAE Desert Weather satellites are generally considered to be the most useful of the lot, since the data is open and not encrypted and the signals are quite strong.  The NOAA operates both geostationary and polar observers.  The geo satellites can only be received if you happen to live in its antenna footprint (North America), while the polar satellites pass overhead twice a day wherever you are. This article describes how to get an image from one of the NOAA polar satellites, using a cheap ($25) little RTL-SDR radio receiver.  These pictures are interesting, since the weather is always changing.  You also need to...