gnuradio – Page 6 – Daniel Estévez

gr-satellites v3.0.0-rc1

In GRCon last year I presented the roadmap for a large refactor of gr-satellites that would eventually be released as gr-satellites v3.0.0. The refactor started near the end of September, and after nearly 8 months I have now arrived at a point where I feel that all the work I’ve done should be packed and released. Not all the ideas I had in my head when I started have made it to the release (some of them require a large amount of work), but I think that the new gr-satellites is still much better than the old one and I would like to start seeing people switching over. Therefore, I have released today v3.0.0-rc1.

Rather than summarising here all the changes that v3.0.0 brings, I invite you to head over to the new gr-satellites documentation and discover by yourselves.

As anything bringing large change, I think that gr-satellites v3.0.0 will probably break some old habits and workflows. However, I hope that it breaks them for good, and that you will find a better workflow with v3.0.0. If not, please head over to the Github issues and let me know what you’re missing in the new release.

A few more notes about project management: starting with this release, I have decided to concentrate all the support and discussion about gr-satellites in the Github issues. This is an idea I’ve stolen from Kate Temkin. In the past I’ve done a lot of discussion with gr-satellites users over email, and while I don’t have any objections to the use of email, Kate makes an extremely good point about the usefulness of having this discussion in public forums. Just the possibility of past issues appearing in Google searches when a user is looking for help makes it worth the effort.

To try to have better coordination with satellite teams planning to use gr-satellites for their missions (a few such as OPS-SAT and Quetzal-1 have already done so), I have written a note for them.

The plan is for v3.0.0-rc1 to become the final v3.0.0 at the beginning of June if no major issues show up. So please go ahead and check out all the new features that v3.0.0-rc1 brings, and let me know in the issues any problems you might find.

Decoding BepiColombo

BepiColombo is a joint mission between ESA and JAXA to send two scientific spacecraft to Mercury. The two spacecraft, the Mercury Planetary Orbiter, built by ESA, and the Mercury Magnetospheric Orbiter, built by JAXA, travel together, joined by the Mercury Transfer Module, which provides propulsion and support during cruise, and will separate upon arrival to Mercury. The mission was launched on October 2018 and will arrive to an orbit around Mercury on December 2025. The long cruise consists of one Earth flyby, two Venus flybys, and six Mercury flybys.

The Earth flyby will happen in a few days, on 2020-04-10, so currently BepiColombo is quickly approaching Earth at a speed of 4km/s. Yesterday, on 2020-04-04, the spacecraft was 2 million km away from Earth, which is close enough so that Amateur DSN stations can receive the data modulation sidebands. Paul Marsh M0EYT, Jean-Luc Milette and others have been posting their reception reports on Twitter.

Paul sent me a short recording he made on 2020-04-04 at 15:16 UTC at a frequency of 8420.535MHz, so that I could see if it was possible to decode the signal. I’ve successfully decoded the frames, with very few errors. This post is a summary of my decoding.

Decoding LES-9

After decoding a recording of the LES-5 236.7MHz telemetry beacon made by Scott Tilley VE7TIL, I have decoded an older recording made by Scott of the S-band beacon of LES-9. This satellite was launched in 1976 and it has a 100 baud BPSK beacon at 2250MHz. Scott twitted about it in April 2019, and in January 2020 he reported that the modulation had stopped and the beacon was now a CW carrier.

I have used this recording made by Scott in 2020-01-13. The GNU Radio demodulator, which is very similar to the one for LES-5, is here and the Jupyter notebook with the results is here. Below, I make a brief summary of the results.

Decoding LES-5

LES-5 is a satellite launched in 1967. It was built by the MIT Lincoln Laboratory and its main payload was an experimental transponder for the military 230MHz band. It was placed in a subsynchrounous orbit with an altitude of around 33400km (GEO altitude is 35786km). Its operations ceased in 1971.

A couple days ago, Scott Tilley VE7TIL discovered that LES-5 was still transmitting, and was able to receive its beacon at 236.749MHz. Scott reports that LES-5 is the oldest GEO-belt object that he knows to be still transmitting.

The beacon is modulated, rather than being a CW carrier, so Scott sent me a short recording for analysis. This post is a summary of my study.

Decoding images from AMICal Sat

AMICal Sat is a 2U cubesat developed by the Space Centre of the Grenoble University, France, and the Skobeltsyn Institute of Nuclear Physics in the Lomonosov Moscow State University. Its scientific mission consists in taking images of auroras from low Earth orbit. The satellite bus was built by SatRevolution. Currently, the satellite is in Grenoble waiting to be launched on a future date (which is uncertain due to the COVID-19 situation).

A few weeks ago I was working with Julien Nicolas F4HVX to try to decode some of the images transmitted by AMICal Sat. Julien is an Amateur radio operator and he is helping the satellite team at Grenoble with the communications of the satellite.

This post is an account of our progress so far.

Fifth alpha for gr-satellites 3

Today I have released gr-satellites v3-alpha4, the fifth alpha in the series that will lead to the refactor of gr-satellites in which I’ve been working since September. This alpha release has been focused on improving the performance of the BPSK and FSK demodulators. Here I summarise the improvements and new features that this alpha brings, and look at the roadmap leading to the release of gr-satellites 3.0.0.

Simulating the TED gain for a polyphase matched filter

Trying to improve the performance of the demodulators in gr-satellites, I am switching to the Symbol Sync GNU Radio block, which was introduced by Andy Walls in GRCon17. This block covers the functionality of all the other clock synchronization blocks, such as Polyphase Clock Sync and Clock Recovery MM, while fixing many bugs.

One of the new features of the Symbol Sync block is the ability to specify the gain of the timing error detector (TED) used in the clock recovery feedback loop. All the other blocks assumed unity gain, which simply causes the loop filter taps to be wrong. However, the TED gain needs to be calculated beforehand either by analysis or simulation, as it depends on the choice of TED, samples per symbol, pulse shaping, SNR and other.

While Andy shows how to use the Symbol Sync block as a direct replacement for the Polyphase Clock Sync block in his slides, he leaves the TED gain as one, since that is what the Polyphase Clock Sync block uses. In replacing the Polyphase Clock Sync block by Symbol Sync in gr-satellites, I wanted to use the correct TED gain, but I didn’t found anyone having computed it before. This post shows my approach at simulating the TED gain for polyphase matched filter with maximum likelyhood detector.

Decoding ESA Solar Orbiter

Solar Orbiter is an ESA Sun observation satellite that was launched on February 10 from Cape Canaveral, USA. It will perform detailed measurements of the heliosphere from close distances reaching down to around 60 solar radii.

As usual, Amateur observers have been interested in tracking this mission since launch, but apparently ESA refused to publish state vectors to aid them locate the spacecraft. However, 18 hours after launch, Solar Orbiter was found by Amateurs, first visually, and then by radio. Since then, it has been actively tracked by several Amateur DSN stations, which are publishing reception reports on Twitter and other media.

On February 13, the spacecraft deployed its high gain antenna. Since it is not so far from Earth yet, even stations with relatively small dishes are able to receive the data modulation on the X band downlink signal. Spectrum plots showing the sidelobes of this signal have been published in Twitter by Paul Marsh M0EYT, Ferruccio IW1DTU, and others.

I have used an IQ recording made by Paul on 2020-02-13 16:43:25 UTC at 8427.070MHz to decode the data transmitted by Solar Orbiter. In this post, I show the details.

Fourth alpha for gr-satellites 3

Shortly after releasing the third alpha, I have released today gr-satellites v3-alpha3, which is the fourth in the series of alphas of the future gr-satellites v3. This release focuses on a new file and image receiver framework that tries to give a general way of reassembling files transmitted in chunks using different protocols.

Third alpha for gr-satellites 3

gr-satellites v3 is a large refactor of the gr-satellites codebase that I introduced in September. Since then, I have been working and releasing alphas to showcase the new features and get feedback from the community. Today I have released the third alpha in the series: v3-alpha2.

Each of the alphas has focused on a different topic or feature, and v3-alpha2 focuses on extending the number of satellites supported and bringing back most of the satellites supported in gr-satellites v2. Whereas previous alphas supported only a few different satellites, this alpha supports a large number. Therefore, I think that this is the first gr-satellites v3 release that is really useful. I expect that interested people will be able to use v3-alpha2 as a replacement of gr-satellites v2 in their usual activities.

In this post, I explain the main features that this alpha brings. For the basic usage of gr-satellites v3, please refer to the post about the second alpha.