F4DAV

Software-defined phased array imaging the geostationary arc at 10489.999600 MHz. Twinkle, twinkle, little QO-100 CW beacon. #amateurradio

@luigifcruz Interesting grating pattern. What's the angular unit ?

This means that the actual fun part is about to begin.

The ability to generate this image is the culmination of 3 years of work. 🤣

@pu3hag @MehdiHacks Interesting indeed. 80 MSPS ADC but you have to use its built-in DDC and decimator because the digital output bus can't stream more than 80 or 160 Mbit/s (from a quick glance at the datasheet). afedri-sdr.com/index.php/down…

@MehdiHacks I *think* Afedri Lan SDR might worth a look too.

Dear ham radio and SDR geeks: Do you know any standalone direct sampling HF SDR? I've only found Reuter Pocket (quoted) None of the direct sampling ones are standalone (e.g. WinRadio, Perseus, Elad etc)

@MehdiHacks Bandscope apparently limited to 384 kHz, which suggests the STM32 never sees the raw ADC stream, not even snapshots for spectrum monitoring. Interesting platform for tinkering though. root:123 :-) github.com/tom-acco/Xiegu…

@MehdiHacks "The new Xiegu X6200 is an ultra-portable direct sampling SDR transceiver for HF and 6m" Couldn't find a screenshot of a 30MHz-wide waterfall though. xiegu.eu/product/x6200/

@jwt0625 Are these useful for fiber optic gyroscopes ? IIRC they have dithering to prevent lock-in between the beams; maybe ultra-stable lasers wouldn't need this ? And can we microfabricate the weird coils too ? x.com/jwt0625/status…

they are not that complicated to make, you have less than 10 different types of components, each with less than 20 parameters that matters. - Heim2026: [Versatile CMOS modulation-free self-isolating stabilizedprecision lasers on a chip](arxiv.org/abs/2602.23160) however it's all analog, and there are a lot of other expensive stuff when you want to use a very good laser for..

if we have more people yearning for really good lasers, these chips that have most components on an optical table shrinked onto them could cost less than 100 bucks.

@hb9vcj Intéressant, les communiqués de presse parlent de réseaux phasés optiques à 1000 éléments. C'est plus que le modèle présenté il y a un an. x.com/jwt0625/status…

Taara Beam construit des liens de données optiques à 25 Gbit/s pour les réseaux maillés urbains digitec.ch/fr/page/taara-…

LLMs were invented for SEO content farms. AGI, for CAPTCHAs. Stable Diffusion, for deepfakes. Quantum computing is for selling fridges. Proof-of-work is for teleporting electricity. Humanoid robots will be for pit fighting. Megaconstellations, for surveillance. Change my mind.

@uhf_satcom Sierracom 7.1 GHz transverter with some unusual microstrip patterns. Credit: Google Lens. vhf.nz/pubs/TradingTa…

RF magic.

@jwt0625 Wow that's a lot of money waiting for the physicists who will invent unjammable communications based on ultra-narrowband optics or squeezed states or entangled pigeons. Any investment tips ? :-)

me: hey gemini, how much optical fiber manufacturing output did fiber-optic guided drones consume in 2025? gemini: blah blah it represents a vanishingly small fraction of total global manufacturing capacity—likely less than 0.1% by volume me: thats bs I heard it was 10%. How plausible is this number? gemini: In 2026, the claim that drones consume 10% of global optical fiber manufacturing capacity is no longer just a rumor—it has become a focal point of industry tension.

@jwt0625 Yeah I was wondering about environmental factors in commercial CSAC specifications. Thermal gradient ? Thermal waves ? Tilt ? Angular rate ? Vibrations ? EMI ? Also, can't shield against relativity (I think 1e-11 is only 1300 m/s or climbing 100 km).

reading it because i saw this cute magnetic shield for CSAC, freq sensitivity on the order of 1e-11/uT. - Hong2020: [Magnetic shield integration for a chip-scale atomic clock](doi.org/10.35848/1882-…)

the CSAC paper figure was from 2003, there is a prototype eval in 2007, and commercialization in 2011.

@xjamesmorris @scott23192 You want an S-band phased array with digital beamforming and polarization synthesis. Then you'll be able to receive HamTV from all the space stations simultaneously, while also monitoring Artemis TT&C from the Moon and running a 24x7 all-sky search for undocumented satellites :-)

@F4DAV @scott23192 I have 76cm and 1.2m dishes. The latter has slew drives & might be too slow for LEO. The 76cm is a little small. Clearly I need another dish with an XY rotator. Right? For science.

Thrilled to get a full 9-seconds of S-Band HamTV video from the ISS today! That's 3 or 4 times more than usual. Nothing changed here other than everything covered in ice for over a week.

@dh2va Not insane, but they still view programming errors as statistical defects ? Should consider domain-specific languages and catching imperial/metric confusions. Which many teams probably already do. Otherwise someone will embed a Javascript interpreter that passes the ten rules.

Arguments don't sound so unreasonable to me.

@DutchSpace Need to fly straight despite asymetric thrust, unbalanced aerodynamics or off-axis center of mass ? Simply roll ! Works for bullets, missiles and fireworks. Seriously, was this done on purpose, or is it an emergent behaviour of their control algorithms ?

No really, LOOK at it...I've never seen a launcher behave like this and have mission success... #USSF87

@scott23192 @xjamesmorris The official recommendation is 1.2m. There is no point in oversizing - you only need enough SNR for your worst case (low elevation, bad weather, edge of TX lobe). For an overhead pass, a fixed 90x60cm WiFi grid antenna can capture a few seconds of DVB-S. ariss.org/hamtv-on-the-i…

@xjamesmorris Hey James! Some people have reported success w/ 80cm dishes, but I'm guessing you'd have to have a perfectly clear view of the sky. Even from LEO, the ISS HamTV downlink is not a strong signal. So, use the largest dish you can to increase odds of success.

@jwt0625 32 GB in flight is about 16 Mbit per mm³ of SMF core. There's plenty of room at the bottom before we reach the holographic bound and the fiber collapse into a black hole. The 20 nm coating on hard disk platters already gets much closer :-)

160 Tb/s over 1040 km - Shimizu2026: [Ultra-wideband, High-capacity Inline-amplified Optical Transmission Using Extremely Long Wavelength Band (X-band)](ntt-review.jp/archive/ntttec…)

@jwt0625 Cool but I couldn't figure how they do pulsed electrical discharge in a vacuum. Their website is pure marketing e.g. "magnifying voltage" (aka DC-DC conversion ?) and "electrostatic energy storage" (aka capacitors ?) and "ESR 10 MΩ" (don't use all-caps). lunarresources.space/helix-driver

theres a cool unlisted video about it - [FarView Radio Observatory](youtube.com/watch?v=FOUAMR…)

100,000 dipole antennas over 200 square km to the moon (it's actually going to be from the moon) - [The Quest to Build a Radio Telescope That Can Hear the Cosmic Dark Ages](spectrum.ieee.org/lunar-radio-te…)

@jwt0625 Maybe they wanted to pitch their "variable density triply periodic minimal surface gyroid matrix lattice" approach to structural design ? I used to dismiss AM because it can't make parts that are very strong, very transparent or very airtight. Good to see progress on the latter.

it still doesn't make sense to AM the whole chamber

what is this, what the heck is this, additive manufactured UHV chamber??? "the chamber can maintain pressures in the 1e−10 mbar range for over two hours without active pumping and that even after 48 h, the pressure remains in the 1e−9 mbar range" ..I guess it makes sense...

@MehdiHacks @lister6520 What about tablets with numerous M.2 slots ? "Handheld wideband spectrum monitor with large display and cute GPU-accelerated waterfall" makes good demos, would be nice if we could DIY it.

@lister6520 Not sure. But it doesn't make sense on a laptop.

New SDR coming soon! "LimeSDR Micro" is offered in 2 form factors: mPCIe and M2. It has more than 100MHz bandwidth. I got a sample board to test and review. Will share the results here. They will soon launch a campaign on CrowdSupply.

@DutchSpace I can't see anything that looks like rigid folded side panels. Could this be a springy mechanism that inverts the curvature, hence the codename EARPOP ? Or maybe Apollo astronauts did secret EVAs to attach the panels on their way to the Moon ?

What is interesting is that the main reflector of the JUMPSAT SIGINT antenna seems to have deployable parts... Comparing the model vs the EMC chamber vs the shaker setup, the EMC chamber pic clearly has the reflector in a "deployed" state, vs folded for the shaker pic...

@jwt0625 So the CTN issue came up in GW detectors as early as 2006, and this led to improvement in clocks ? Amazing engineering. doi.org/10.1364/AO.45.… I wonder how much the amateur photography market would pay for ultra-low-noise non-amorphous single-quartz-crystal lenses :-)

people don't appreciate 1e-18 fractional accuracy enough. It took decades of development pushing many things to the extreme. For example, let's take a look at the optical cavity used for stabilizing the laser used for these atomic clocks. The most recent fight they had with the cavity is replacing the dielectric coating (sputtered SiO2/Ta2O5 or TiO2), which is amorphous, to stacks of crystalline GaAs/AlGaAs, because crystals have lower thermal mechanical noise than amorphous materials, and they got a cavity with 2.5e-17 stability with such quieter mirror coatings. [Lee2026] How good is 2.5e-17? When you are here, you are at the extreme opposite of "nothing ever happens". Everything is happening, and everything affects you. Temperature? It gives you at least two big headaches, (temperature fluctuation) * (thermal expansion), and thermal noise itself. So you optimize the cavity shape, you use single crystal for both the mirror spacer as well as the mirrors themselves so they are less lossy and thus less noisy, and you bond them together along the same crystal orientation as closely as possible. You also cooldown the cavity to reduce thermal noise, not only that, but you also operate at the CTE zero crossing point so temperature fluctuation matters less, thats why you see 124 K and 17 K for silicon cavities. Even with zero CTE, you still need few mK temperature control. Away from zero CTE, it may need to be stabilized to sub uK level. If you glance into cavities working at 4 K (i.e. small but not at zero CTE), you'll see crazy thermal damping systems to smooth out the temperature fluctuation of the 4 K cryostat (~20 mK), as well as find claims like "we now require only mK level control of the room temperature enclosure". [Zhang2017, Robinson2019] (they said "only" because some older cavities were at room T and controlled to sub mK [Ludlow2007], and they got tricks to reduce effects from room T.) (temperature gradient also gives you headache, which is why they choose silicon over glass, for its much higher thermal conductivity) Next is vibration/acceleration. Nothing is rigid, the cryostat vibrates, the earth rotates, and your cavity changes shape. Thats another motivation for silicon over glass, for its higher Young's modulus. So you make the cavity shape as symmetric as possible, and make the mounting fixture as symmetric as possible, and align them with the crystal axis because silicon's Youngs modulus not isotropic . Thus you also choose the optical axis to be the crystal axis with the highest Young's modulus. [Kessler2012] You also gotta align the mechanical axis with the optical axis and with the crystal axis, otherwise longitudinal acceleration would tilt the mirrors and change cavity length. The spacer shape is also a double cone so that it sags less and bends less under transverse acceleration. [Millo2009] Any mechanical resonance would be bad, so you also gotta use PEEK instead of PTFE for supporting the mounting ring, and push the lowest mechanical resonance to be as high freq as possible. Remember silicon's crystal structure? Remember its 3-fold rotational symmetry? That's why your support structure also has the same 3-fold symmetry. [Matei2016] If you have done all these properly, congratulations, now you might be ready to start fighting thermal noise in the dielectric mirror coatings. Harry2002: [Thermal noise in interferometric gravitational wave detectors due to dielectric optical coatings](doi.org/10.1088/0264-9…) Numata2004: [Thermal-Noise Limit in the Frequency Stabilization of Lasers with Rigid Cavities](doi.org/10.1103/PhysRe…) Ludlow2007: [Compact, thermal-noise-limited optical cavity for diode laser stabilization at 1e-15](doi.org/10.1364/OL.32.…) Millo2009: [Ultrastable lasers based on vibration insensitive cavities](doi.org/10.1103/PhysRe…) Hopcroft2010: [What is the Young's Modulus of Silicon?](doi.org/10.1109/JMEMS.…) Kessler2012: [A sub-40-mHz-linewidth laser based on a silicon single-crystal optical cavity](doi.org/10.1038/nphoto…) Matei2016: [A second generation of low thermal noise cryogenic silicon resonators](doi.org/10.1088/1742-6…) Zhang2017: [Ultrastable Silicon Cavity in a Continuously Operating Closed-Cycle Cryostat at 4 K](doi.org/10.1103/PhysRe…) Robinson2019: [Crystalline optical cavity at 4 K with thermal-noise-limited instability and ultralow drift](doi.org/10.1364/OPTICA…) Lee2026: [Frequency Stability of 2.5×10^−17 from a Si Cavity with AlGaAs Crystalline Mirrors](doi.org/10.1103/zgrm-c…)