Receiving Arecibo in HF

The well known Arecibo observatory, besides being used as a radiotelescope and planetary radar, has a powerful HF transmitter that is used to artificially excite the ionosphere, in order to study ionospheric effects using 430MHz incoherent scatter radar. More information about this can be found in the HF proposals page of the observatory web, and in this poster that details the characteristics of the HF facilities.

The HF transmitter has a power of up to 600kW and can use the frequencies 5.1MHz and 8.175MHz. At those frequencies, the dish has a gain of 22dB (13º beamwidth) and 25.5dB (8.5deg) respectively, so the power that is beamed up to the ionosphere is huge. The 430MHz incoherent scatter radar is even more powerful, with up to 2MW. For an introduction to ionospheric incoherent scatter radar, see this lecture by Juha Vierinen, which explains why such huge powers are needed, due to the very weak radar return of ionospheric plasma.

A few days ago, on Wednesday 24, Chris Fallen tweeted that the Arecibo transmitter was active at 5.1MHz. According to the telescope schedule, which can be seen in the figure below (click on the image to view it in full size), there was an experiment that involved the HF transmitter on 2020-06-24 from 18:00 to 22:00 UTC, on 2020-06-25 from 17:00 to 21:00 UTC, and on 2020-06-26 from 17:00 to 21:00 UTC.

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Ranging through the QO-100 WB transponder

One of the things I’ve always wanted to do since Es’hail 2 was launched is to perform two-way ranging by transmitting a signal through the Amateur transponder and measuring the round trip time. Stefan Biereigel DK3SB first did this about a year ago. His ranging implementation uses a waveform with a chip rate of only 10kHz, as it is thought for Amateur transponders having bandwidths of a few tens of kHz. With this relatively slow chiprate, he achieved a ranging resolution of approximately 1km.

The QO-100 WB transponder allows much wider signals that can be used to achieve a ranging resolution of one metre or less. This weekend I have been doing my first experiments about ranging through the QO-100 WB transponder.

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Decoding Crew Dragon Demo-2

The launch last Saturday of Crew Dragon Demo-2 undoubtedly was an important event in the history of American space exploration and human spaceflight. This was the first crewed launch from the United States in 9 years and the first crewed launch ever by a commercial provider. Amateur radio operators always follow this kind of events with their hobby, and in the hours and days following the launch, several Amateur operators have posted reception reports of the Crew Dragon C206 “Endeavour” signals.

It seems that the signal received by most people has been the one at 2216 MHz. Among these reports, I can mention the tweets by Scott Tilley VE7TIL (and this one), USA Satcom, Paul Marsh M0EYT. Paul also managed to receive a signal on 2272.5 MHz, which is not in the FCC filing, so this may or may not be from the Crew Dragon.

Scott has also shared with me an IQ recording of one of the passes, and as I showed on Twitter yesterday, I have been able to demodulate the data. This post is my analysis of the signal.

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LES-5 telemetry Grafana dashboard

Scott Tilley VE7TIL is making a serious effort and a great job of recording and processing LES-5 telemetry. He is recording all the passes over his home in western Canada (which last several days, due to the sub-synchronous orbit), and sharing the data on a Github repository, together with Jupyter notebooks that analyse the data and plot some of the telemetry variables, such as the values recorded by the RFI experiment.

I am storing this data in InfluxDB 2.0 and using Grafana to plot it and explore it. The Grafana server has been running for quite some time now, but I never announced it publicly, so very few people have used it. I guess that now is a good time to share it with a wider audience. The server is at eala.destevez.net:3000 and the LES-5 dashboards can be accessed by using user “les5” and password “les5”.

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Update on the QO-100 local oscillator wiggles

This post is a follow up to my study of the “wiggles” observed in the local oscillator of the QO-100 NB transponder. After writing that post, I have continued measuring the frequency of the BPSK beacon with my station almost without interruptions. Now I have some 44 days of measurements, spanning from April 9 to May 23. This data can be interesting to look at, so I’m doing this short post to share the data and look at it briefly.

The Jupyter notebook with all the data can be found here. The data is also linked in my jupyter_notebooks Github repository, which now uses git-annex to store the data in my home server. See the README for instructions on how to download some or all of the data files in the repository.

The whole time series can be seen in the figure below. We note that the typical Doppler sinusoidal curve varies slowly due to orbit perturbations and sometimes suddenly as a consequence of a station-keeping manoeuvre. I tweeted about one of the manoeuvres a while back.

There are now too many days in order to see things clearly when the frequency curves for each day are overlaid, but hopefully the figure below gives a good idea. We can see that the wiggles still happen approximately between 21:00 and 06:00 UTC, and between 11:00 and 17:00 UTC.

If we add an artificial offset of -15 Hz per day to the curves to prevent them from overlapping, we obtain the figure below. We see that the pattern of the wiggles keeps changing slightly, but also remains quite similar.

In my last post about this topic I said that it seemed that the wiggles repeated with a period of a sidereal day. Now it is clear that it is not the case. The wiggles seem to repeat roughly with a period of a solar day (24 hours). In fact, in 44 days sidereal time “advances” 2.88 hours with respect to solar time. However, it is clear that the wiggles haven’t shifted that much in time.

Wiggles in the QO-100 local oscillator

Some days ago, Hans Hartfuss DL2MDQ sent me an email about some frequency measurements of the QO-100 NB transponder BPSK beacon that he had been doing. The BPSK beacon is uplinked from Bochum (Germany) through the transponder, and as the beacon is generated using a very good Z3081A GPSDO as a reference, the frequency drift observed on the beacon downlink is caused by Doppler and the drift of the local oscillator of the transponder.

In his measurements, Hans observed some small oscillations or “wiggles” that didn’t seem to be caused by Doppler. Decided to investigate this, I started to do some measurements of my own. This post is an account of my measurements and findings so far.

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LES-5 RFI experiment telemetry

In previous posts, I have talked about the attempts of decoding LES-5 telemetry done by Scott Tilley VE7TIL and me. Now Taylor Bates KN4QGM has joined us in our efforts, and with their help I think I have figured out most details of how the telemetry of the RFI experiment works. One of the payloads of LES-5 was a radio frequency interference experiment that scanned the 255-280 MHz band and made spectrum measurements. The receiver of this experiment was also used as the telecommand receiver for the spacecraft. We are very interested in studying the telemetry of this RFI experiment to see to what extent the receiver is working and if the spacecraft could actually receive commands.

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Idle data in BepiColombo X-band signal

Yesterday I posted about decoding the data in an X-band recording of BepiColombo. I only made a very shallow analysis of the data, which consisted of CCSDS TM Space Data Link frames. However, I showed that most of the data was transmitted on virtual channel 7. A few hours later, Oleg_meteo in Twitter noted that this data in virtual channel 7 was just a 511 bit PN sequence. After some analysis I’ve confirmed what Oleg_meteo said and shown another interesting and unexpected property of this data.

All the Space Data Link frames in virtual channel 7 have a first header pointer field of 2046, which means “idle data only”. When the payload in these frames is concatenated (there are 8792 payload bits per frame) we obtain an infinite sequence that fits the following description.

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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.

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More data from LES-5

Yesterday I looked at decoding some data transmitted by LES-5. Today I have analysed a longer recording made by Scott Tilley VE7TIL to perform an eclipse timing on 2020-03-25. The study has been done in this Jupyter notebook, which looks at the sequences of symbols extracted before and after the eclipse (they are kept as two separate sequences because the transmit frequency changed slightly after the eclipse, so decoding required two separate passes).

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