Daniel Estévez

Everything space & RF. Amateur radio operator (EA4GPZ / M0HXM). PhD in Mathematics from. he/him

Blog: https://destevez.net
Twitter: https://twitter.com/ea4gpz
Keyoxide: aspe:keyoxide.org:MPXJS6MJRS3LENLWBNOOAMHOMY

Public Key

npub1u5exd4naj5cq5yfr87dl8c33pswsvl54mpx3gzrcn8paza22genskh4glf

NIP-05 Address

destevez_at_mastodon.social@momostr.pink

Profile Code

nprofile1qqsw2vnx6e7e2vq2zy3nlxlnugcsc8gx062asng5ppufns73w49yvecpz3mhxue69uhhyetvv9ujuerpd46hxtnfduqs6amnwvaz7tmwdaejumr0ds0049gv

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nostr.wine

relay.damus.io

nos.lol

Author Public Key

npub1u5exd4naj5cq5yfr87dl8c33pswsvl54mpx3gzrcn8paza22genskh4glf

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Last Notes

2025-04-20 08:58:36 UTC

New blog post: Analysis of the CAMRAS Venus radar experiment. A deep dive into the Earth-Venus-Earth L-band radar experiment done in March by @npub1cuv…u7h5, Astropeiler Stockert, the Deep Space Exploration Society, and @npub1j94…l9ea.
I show how to compute the radar Doppler with SPICE and come up with a Doppler spread model based on an S-band scattering model from Arecibo. I explain why the maximum surface Doppler offset is 8.6 Hz even though the rotational velocity predicts 15.7 Hz.
https://files.mastodon.social/media_attachments/files/114/369/461/501/691/078/original/8b098a955706008f.png
https://files.mastodon.social/media_attachments/files/114/369/461/798/697/741/original/b20f47f45cdc0f47.png

2025-02-22 22:31:24 UTC

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OSNMA (the Galileo authentication system) is not a paid service. Anyone can use it. But it only authenticates ephemeris data. It doesn't offer full protection against spoofing. Better protection is given by cryptographic GNSS signals, which are only available to authorized users (i.e., the military, law enforcement, etc.)

2025-02-22 21:32:09 UTC

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it could even happen by accident. One constellation might have a problem that makes the satellites broadcast bad clock and ephemeris data without marking the satellites as unhealthy.

2025-02-22 21:27:18 UTC

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Bert mentioned one constellation broadcasting "odd data", but not jamming the others. At least that's how I understood it.

2025-02-22 20:33:28 UTC

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I'm almost surprised that no one has run the experiment (at least I haven't seen it in the literature). It looks like an easy way to get a paper published.

2025-02-22 19:38:49 UTC

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and before anyone jumps at me, yes, I do understand that the newer GPS satellites don't even support Selective Availability, but there are many other hypothetical ways of degrading the civilian service. This is mostly intended as a thought experiment.

2025-02-22 19:37:02 UTC

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Galileo is great, but people speak about resilience, sovereignty and independence way too soon without thinking about all the technical nuances. Most consumer devices are multi-constellation and use GPS, GLONASS, Beidou and Galileo. They are not very configurable and not very smart. I wonder what would happen if the US decides to turn Selective Availability back again (that's a mechanism that greatly degrades the civilian GPS positioning accuracy).

2025-02-15 10:50:35 UTC

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It has been a long time since I last used my OSNMA software in this microcontroller (the microcontroller firmware was mostly intended as a tech demo), so I had to search around for my UART TLL to USB adapter.
Check out my galileo-osnma Rust project: https://github.com/daniestevez/galileo-osnma/

2025-02-15 10:50:04 UTC

Testing again Galileo OSNMA on a small RISC-V microcontroller. [@bob_n6rfm](https://mastodon.social/@bob_n6rfm ) wanted some help troubleshooting his system, so I built and tested a known-good firmware image for him. The Galmon data feed is down, so I'm using my own uBlox receiver.
https://files.mastodon.social/media_attachments/files/114/007/512/262/812/913/original/fde12f5776172bc3.png

2025-02-02 07:47:18 UTC

I'll be all Sunday roaming around FOSDEM. If someone wants to meet, just ping me.

2024-12-13 07:15:00 UTC

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that is striking to hear. I finished my PhD in 2017, and while I studied I have even gone to the library to try to find a result I needed (some type of inequality) by looking through the books in the harmonic analysis section, figuring from the title on their spine if they might contain something related, and quickly browsing through a few of them. I didn't find the result I was looking for, but certainly this way of searching you couldn't do online.

2024-11-10 21:08:22 UTC

New blog post: Decoding Hera. I report about the recordings I did of the Hera X-band telemetry with the Allen Telescope Array shortly after launch and show how to decode them with GNU Radio.
https://files.mastodon.social/media_attachments/files/113/460/700/337/710/403/original/48a00a66c06b5168.png

2024-10-18 20:14:41 UTC

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The telemetry is AOS frames and Space Packets. The idle packets contain an Easter egg message with the names of the team members. There are many similarities in the telemetry with Psyche, the previous NASA mission.
Read more: https://destevez.net/2024/10/decoding-europa-clipper/

2024-10-18 20:14:06 UTC

New blog post: Decoding Europa Clipper. A summary of my observation with the Allen Telescope Array after the launch, including a @npub1xp6…hh9m decoder and the IQ recording. Some highlights: the modulation and coding is PCM/PM/NRZ r=1/6 Turbo with 1115 byte frames.
https://files.mastodon.social/media_attachments/files/113/330/253/721/432/651/original/eae941ff3b91ef66.png

2024-10-15 19:51:19 UTC

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I now managed to find an idle packet containing the complete message. The ending is a very nice touch.
https://files.mastodon.social/media_attachments/files/113/313/177/160/561/443/original/29e63614a8992643.png

2024-10-14 20:34:03 UTC

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The observation has just finished. Taking a quick look at the recording now. The same 12 kbaud r=1/6 Turbo 1115-byte frame modulation and coding has been maintained all the time. Idle Space Packets are "signed" by team members. Congratulations to them and the rest of the team!
https://files.mastodon.social/media_attachments/files/113/307/683/309/186/013/original/f55aa6e6cebc8e6c.png

2024-10-14 17:46:14 UTC

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What looks like ranging tones has now appeared on the signal.
https://files.mastodon.social/media_attachments/files/113/307/022/996/485/054/original/1088494ddf3cabe4.png

2024-10-14 17:41:28 UTC

We are tracking Europa Clipper with one 6 meter antenna at the Allen Telescope Array. Massively strong telemetry signal. Interestingly for such a low rate telemetry signal, there is no subcarrier.
https://files.mastodon.social/media_attachments/files/113/307/004/041/167/516/original/a6312f8234444137.png

2024-09-20 20:46:49 UTC

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Remember that this is a dB scale. Some of the LOFAR measurements suggest that Starlink v2 can be up to 40 dB above the EMI limits for the automotive sector. Let me know if I made any mistakes with the calculations or if if you have more perspective on radiated EMI measurements.

2024-09-20 20:46:35 UTC

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So we have 78.2 dB μV/m at 3 m and 67.8 dB μV/m at 10 m (both in 120 kHz bandwidth). Comparing with typical radiated EMI limits, this seems like a lot. For instance https://ti.com/lit/wp/slyy142/slyy142.pdf gives 22 μV/m at 10 m with an average detector (LOFAR also measured average power).
https://files.mastodon.social/media_attachments/files/113/171/836/368/677/513/original/f642ef12229eff77.png

2024-09-20 20:45:42 UTC

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The free space path loss at 1000 km (a typical slant range for a LEO satellite) and 60 MHz is -128 dB. So the transmitted EIRP is -17 dBm / 120 kHz. My background is in communications, and this sounds like a lot for an unwanted emission. Let's put it in perspective. EMI limits are measured in dB μV/m at 3 or 10 m distance. The conversion formula at 3 m is dB μV/m = EIRP(dBm) + 95.2 (https://yorkemc.com/wp-content/uploads/How_to_-_EIRP.pdf). Going from 3 m to 10 m the field strength decreases by -10.4 dB = 20log10(3/10).

2024-09-20 20:45:07 UTC

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We'll calculate things in 120 kHz bandwidth, because apparently that's the standard to measure EMI below 1 GHz (I know much more about communications than EMI, so do correct me if I make mistakes). We'll also normalize things for an isotropic 60 MHz antenna. An isotropic antenna has an aperture of λ²/(4π), which for 60 MHz gives 1.99 m². Thus the received power with such antenna in 120 kHz bandwidth is -145 dBm, which is obtained as -230+10*log10(1300 * 120e3 * 1.99).

2024-09-20 20:44:36 UTC

I'm starting to read the paper about Starlink v2 VHF EMI received with LOFAR that recently made the rounds. Accompany me in doing some calculations to understand how strong this EMI actually is. I'm comfortable with Jy, dBm and such, but use them in radically different contexts. So I need to convert to understand how strong something is. The paper mentions up to 1300 Jy between 56 and 66 MHz (let's call it 60 MHz). Recall that 1 Jy is -230 dBm per Hz of bandwidth and m² of receiver aperture.
https://files.mastodon.social/media_attachments/files/113/171/828/172/102/448/original/61c2c394ea904e87.png

2024-08-22 07:16:45 UTC

New blog post: JUICE Earth flyby. I report on my failed attempt to receive the X-band telemetry with the Allen Telescope Array during the flyby, presumably because the spacecraft transmitter was off. https://destevez.net/2024/08/juice-earth-flyby/
https://files.mastodon.social/media_attachments/files/113/004/443/631/481/700/original/41cfcc0cce2913ca.png

2024-08-19 19:50:39 UTC

New blog post: Final update for the Galileo GST-UTC anomaly. In September-October 2023 I was covering an anomaly where the Galileo system time deviated much more than usual from UTC. Now that the event is long finished, I have updated my data analysis to show the full extent.
Read more: https://destevez.net/2024/08/final-update-for-the-galileo-gst-utc-anomaly/
https://files.mastodon.social/media_attachments/files/112/990/419/693/015/417/original/f4afb35e63994fe9.png