The March AMSAT-F Recontre Spatiale (Space Meeting) 2019 was not only a conference about amateur satellite communications, but a conference which took place over amateur satellite communications – using Lime Microsystems’ LimeSDR hardware.
Taking place on the 9th and 10th of March 2019, the second AMSAT-F Recontre Radiomateur Spatiale saw 15 lectures and six short presentations on the topic of amateur satellite communications from a total of 20 contributors. While attendance in person was certainly recommended, for those a little further away there was another option: reception of a live transmission sent via the Es’hail-2 QO-100 satellite’s amateur transponder.
Evariste Courjaud was responsible for configuring the modulation part of the transmission setup. “The chain was: a PC running Vmix (video mixer) to NDI [Network Device Interface] (over Ethernet) to a PC modulator. On the PC modulator: NDI to ffmpeg H.264 encoder to lime_dvb to a LimeSDR Mini to DVB-S2,” Courjaud explains, using software from the open-source limesdr_toolbox project. “Then the power amplifier: DVB-S2 to a preamplifier to a 150W 2.4 GHz PA to a 1.4 metre dish.”
Using this stack of open-source utilities, hardware, and the compact LimeSDR Mini, the AMSAT-F conference was able to transmit to the amateur transponder on the Es’hail-2 satellite – designated QO-100 – and send video and audio of the event across the world. Transmitting, however, is only half of the equation – and the LimeSDR family proved its worth on the receive side, too.
“I heard about the broadcast on Twitter, probably a retweet of the announcement by AMSAT-F,” explains Daniel Estévez, who announced his success at receiving and decoding the transmission via Twitter. “I tuned to most of the talks on Sunday, and I had them playing on the TV (using a cheap Chinese set-top-box that happens to be able to tune to the IF used for Es’hail-2) while I was working in my shack. However, I don’t speak French. Knowing Spanish, I can understand a little, but not enough to follow a talk. So I had the talks at background to look at the slides every once in a while.”
Having received the broadcasts live using off-the-shelf hardware, Estévez turned his attention to signal capture and offline decoding. “I use the following hardware: A 1.2m offset dish from diesl.com; an Avenger PLL-321S-2 LNB which has been modified to feed an external 27 MHz reference; a 10 MHz GPSDO by DF9NP; a 27MHz PLL by DF9NP to generate the 27 MHz reference for the LNB from the GPSDO 10MHz; a Chinese set-top-box to feed DC (and sometimes the 22 kHz tone) to the LNB; a splitter and DC block to feed the IF of the LNB to the LimeSDR; A LimeSDR, using the 10 MHz GPSDO as reference. Regarding the software, I used: GNU Radio, together with gr-osmosdr and SoapySDR to get samples from the LimeSDR; leandvb to receive DVB-S2; VLC to play the video.”
The result: the ability to capture and decode the video and audio from the talks on demand, including one on amateur satellite regulation by Sylvain Azarian. “I was especially interested in Sylvain’s talk because I have also been working in regulations of amateur satellites,” Estévez explains, “so I tried to follow his talk more carefully.”
Amsat for Beginners
“I am quite happy with the LimeSDR, not only for this kind of works, but for most of my experiments involving SDRs,” adds Estévez.”The features I value the most are the large frequency coverage and large bandwidth, the two full-duplex coherent channels, the possibility of using an external reference, and of course the low price. I also have a LimeSDR Mini which I am quite happy with as well.
“I would encourage anyone to give this a try. If you already have a LimeSDR or a similar SDR supporting large bandwidths, you already have the most expensive piece of equipment. The rest is standard equipment for satellite TV and it is really inexpensive. Once you have the SDR and the satellite dish and LNB, the rest can be done in software (so far using leandvb, but the AMSAT-NA Phase 4 Ground project is also doing a lot of work with DVB-S2 support in GNU Radio, so I expect we will see amazing things from them in the future), so it is very easy to try out new things and to learn a lot (DVB-S2 is a complex and state-of-the-art technology).
“Also, another related activity that can be done with a LimeSDR and a satellite dish and LNB is tuning across the Ku band. The 56 MHz bandwidth of the LimeSDR helps to see a lot. You can use it as a spectrum analyser and see full commercial DVB-S2 multiplexes, which are usually transmitted at 27 Msps. It is also interesting to look out for the narrower packetised traffic and the beacons. Very interesting signals can be seen.”