Hacker News: madengr

New comment by madengr in "Hybrid beamforming receiver dynamic range theory to practice"

madengr — Thu, 30 Nov 2023 18:46:10 +0000

Nice report. I wish beamformer ICs were made for lower frequencies, but everything is targeting X-band and higher.

New comment by madengr in "Reasonable GPUs"

madengr — Sun, 26 Nov 2023 19:55:24 +0000

I’m using 4x A6000 Ada cards for EM simulation. They have 48 GB ECC and 2-slot width so can be accommodated in a server case, versus 24 GB non ECC and 3-slot width for the 4090. They are actually faster for FP32 than the A100, but really poor for FP64.

New comment by madengr in "The Cassette-Tape Revolution"

madengr — Sun, 19 Nov 2023 21:27:41 +0000

Watch there now be a cassette renaissance like there was a record renaissance, despite the cassette having horrible audio quality compared to a CD.

New comment by madengr in "Lockheed is now tracking phones and walkie-talkies from space"

madengr — Sun, 19 Nov 2023 03:09:16 +0000

Most antennas actually have a large radar cross section (RCS), with simple dipoles being some of the worst. An infinitely thin dipole (a current filament) has a non zero RCS even though it has no physical cross section.

In theory, a reflector antenna can have a zero RCS, so putting a reflector behind a dipole will reduce the RCS. It’s totally non-intuitive.

New comment by madengr in "Now that cars are like smartphones, we don't really own them"

madengr — Sat, 11 Nov 2023 21:39:28 +0000

Don’t buy the damned things. I just bought a 1989 Toyota pickup. Manual transmission, locks, windows, etc. Super reliable and easy to work on. It’s got a standard double-DIN stereo opening, so you could install the latest touch-screen gizmo if desired.

New comment by madengr in "Cup Noodles are now microwave-safe"

madengr — Sat, 04 Nov 2023 21:25:50 +0000

Expanded polystyrene has an extremely low loss tangent and dielectric constant, so I fail to see how microwave heating causes more chemical leaching than hot water.

New comment by madengr in "Moonbase Alpha Travel Tube Details"

madengr — Tue, 31 Oct 2023 23:36:07 +0000

The 1973 movie Genesis II also had travel tubes on a post-apocalyptic earth.

For my 5th Xmas I still remember getting a giant Eagle ship. The cockpit was removable from the center structure and the pilots could eject.

New comment by madengr in "SDRangel: Explore the electromagnetic spectrum with open source SDR software"

madengr — Sat, 28 Oct 2023 02:43:38 +0000

I wrote this years ago with that intent, though I don’t know you’d get audio back in real-time.

https://github.com/madengr/ham2mon

New comment by madengr in "WebSDR – Internet-connected Software-Defined Radios"

madengr — Thu, 26 Oct 2023 23:38:14 +0000

I have one too, on an active magnetic loop, which does a decent job of nulling near field interference.

http://kiwisdr.lounix.net:8073/

New comment by madengr in "OS/2 Warp, PowerPC Edition"

madengr — Fri, 20 Oct 2023 10:17:38 +0000

Not only that, but being able to play Doom (or maybe it was Wolfenstein) while downloading at 14.4k was amazing. I believe I used PMComm and of course a 16550 serial card.

I used it extensively in college in early 90’s, as Windows 3.1 seemed so primitive, but then a couple of years later Linux kind of took everything by storm.

New comment by madengr in "NY Bill Would Require Background Checks to Buy 3D Printers"

madengr — Mon, 16 Oct 2023 22:01:04 +0000

I’d expect nonetheless from NY, where they trample on constitutionally guaranteed rights as much as possible.

Maybe they should require all STL and Gcode to be submitted to the state for review.

New comment by madengr in "Signal Identification Wiki"

madengr — Fri, 13 Oct 2023 13:46:22 +0000

Yes, there are companies specializing in this:

https://www.deepsig.ai/

New comment by madengr in "A new era for Arecibo"

madengr — Fri, 29 Sep 2023 17:22:34 +0000

You know how Nyquist says you must sample at minimum twice your highest "frequency" or your get aliasing in your spectrum? It's the same with antennas except you must sample at least 1/2 your wavelength or you get grating lobes (the equivalent of aliasing) in you far field pattern; it's all the same math. A sample in time is equivalent to an antenna element sampling space. A big reflector is equivalent to sampling everything at once with no gaps; it's bandwidth independent. You can only put array element so close together, limited by the size of the element (itself is limited to a fraction of the lowest wavelength), electronics, and unwanted inter-element coupling (though there are tricks to take advantage of this coupling and make very wideband arrays).

If you leave "gaps" in your array elements, that's not a problem receiving strong, periodic signals. You can physically move the elements to fill in the gaps to remove those lobes; the equivalent of an equivalent time oscilloscope or a synthetic aperture radar. The problem is you can't do that when transmitting since you only have one opportunity to send something (non-periodic).

There are other disadvantages with phased arrays. Each amplifier has to be matched in amplitude and phase. I've had to bin lots of amplifiers as some have phase compression and some phase expansion over amplitude. That distorts the pattern over the pulse.

On the receive side, each receiver has thermal noise un-correlated with the others. So for N antenna elements, you received signal-to-noise scale proportional to sqrt(N) instead of N like you have on transmit, or with a big reflector. This is why arrays suck for very weak signals. Notice NASA keeps building big dishes for their DSN instead of "cheaper" arrays.

Then there's the whole timing and phase noise issue with distributing an oscillator.

Tough you can only make a reflector with about 100 dB gain.

New comment by madengr in "A new era for Arecibo"

madengr — Fri, 29 Sep 2023 16:41:44 +0000

It had a powerful transmitter for radar work, and there are advantages to having a single, giant aperture when it comes to maintaining low sidelobes, power amplifier coherency, etc.

New comment by madengr in "LibrePCB"

madengr — Fri, 29 Sep 2023 01:00:51 +0000

Comprehensive part libraries are not an issue. It just needs a basic set of symbols. Most people doing PCB design will create their own symbols and footprints. Altium has an excellent footprint generate, which you can then tweak the output.

New comment by madengr in "America's advanced manufacturing problem and how to fix it"

madengr — Sun, 17 Sep 2023 03:34:09 +0000

Saving is futile with a 3% loss on your money each year. Unless you invest it you are losing it.

New comment by madengr in "UK air traffic control meltdown"

madengr — Tue, 12 Sep 2023 11:08:13 +0000

I was doing some orientation sensing 20 years ago with an IMU and ran into the same problem. I had never known at the time it was gimbal lock (which I had heard of) but did read quaternions were the way to fix it. Pesky problem.

New comment by madengr in "Oscilloscope watch ships after 10 years on Kickstarter"

madengr — Tue, 05 Sep 2023 00:57:19 +0000

“Now you can tell time and measure current on the go.”

So it comes with current probe built into the band?

New comment by madengr in "Ask HN: In person industry tours and site visits?"

madengr — Mon, 04 Sep 2023 23:43:13 +0000

Look up Engineering Explorer Post for high schools students. Each month the attend a presentation on an engineering discipline, and the a site tour. My kid got to visit a nuclear reactor, food packaging manufacturer, biomedical device development, aircraft maintenance depot, etc.

New comment by madengr in "Casio G-Shock time sync radio"

madengr — Wed, 16 Aug 2023 23:30:59 +0000

This is mine. Select the timecode decoder:

http://kiwisdr.lounix.net:8073/