gabesk

In the simplest analogy, it's just the TV rabbit ears with two wires in opposite directions, except much longer wires, because the frequencies are lower and therefore the wavelength is larger. Those classic rabbit ears are effectively a dipole antenna, which is basically: "stretch a wire out in a line so it's half the wavelength of the frequency you want to receive or transmit on, cut it in half, and send the signal from the middle, out both ends of the cut wire".

https://www.aa5tb.com/dipole.html

Picking that length of wire results in the lowest impedance (kind of analogous to friction) at the radio for pushing signal out to the antenna, but various lengths work with more or less efficiency, and you don't have to send the signal from the middle either if you have appropriate inductors and capacitors to adjust the impedance (it's just the simplest way).

As with most things on the internet these days, it seems the best content is in the form of YouTube videos, so amusingly, this is the best written information I came across after some quick searching:

https://apps.dtic.mil/sti/tr/pdf/AD0684938.pdf

Kernel drivers, too. Especially the DMA buffers for devices that don’t support scatter gather: if you don’t allocate them at driver startup, you might not be able to find enough free contiguous regions later. Although maybe that’s not as big of a deal these days, since both Windows and Linux can relocate physical pages.

For small amounts of text, another simple way is to paste it into the Run dialog (Winkey-R) and then copy it back out again. Works well for turning URLs into plain text and removing the editor formatting from function names before pasting into a bug report, for example.

Just FYI that the link to the page about the case against ultrasonic humidifiers is broken; it's missing the / after the domain. I tried leaving a comment on the page, but even after creating a dummy profile it wouldn't accept it, so hopefully you'll see it here.

Not just the first day, but the very first run. They cheaped out and didn't build a bypass for a 30 MPH curve on an otherwise 80 MPH run. Which, while embarrassing enough, shouldn't have resulted in an accident even if the conductor missed the signage as they did, but wasn't because the railways successfully lobbied to delay rolling out Positive Train Control for a few more years. The entire event was just a perfect illustration of the disastrous state of passenger train transit in this country.

[1] https://en.wikipedia.org/wiki/2017_Washington_train_derailme...

As I understand it (and I'm not an expert just curious reader), it's part of what ATSC 3 is fixing by moving to OFDM instead of 8-VSB. Multipath in OFDM leads to some (hopefully few) number of subcarriers fading out, which error correction can manage. Conversely, 8-VSB is a regular single carrier (ish) (with 8 different analog signal levels, hence the name), so in order to decide the value of any bits at all the TV needs to identify and delay (line up) many of the ghosts up with the main signal. That's a more challenging signal processing task, especially given the diversity in age of the TV tuners (the ones from the late 2000's didn't have as advanced DSPs).

Charles Poynton has good references on this. His website is very 90s, but his books (a la Digital Video and HD) are the best clearly explained introduction to color science and gamma vs linear light coding that I've ever read.

https://www.poynton.ca/Poynton-color.html

Kindred souls. About three years ago, I did the same, but with NTSC. In my case I actually built a digitization board that sampled the signal from a composite cable and dumped the raw samples over USB using the Cypress EZ-USB2 chip. I didn't want to "cheat" with a chip that did the synchronization etc. :)

I never really finished it, but I threw a little bit of it on GitHub: https://github.com/gabesk/tv_python is the prototyping version (the raw data is a picture of Lena on a Raspberry Pi composite output).

Also as an aside, if anyone ever wants an example of how to stream data from an isochronous endpoint on Windows, this took me way to long to figure out: https://github.com/gabesk/tv/blob/master/actual_implementati... (see usb_reading_thread routine) as well as this blog post: https://gabesk.blogspot.com/2018/08/streaming-from-isochrono... (that version does real-time black and white, but I never finished real-time color as my laptop at the time couldn't handle it with my poorly optimized decoding routines).

You all have inspired me to finish this properly and publish it. Maybe even as a top level post on HN.

I'm also about that far away and walked through there last night. It felt more like a summer street fair festival. I also took a few pictures. https://photos.app.goo.gl/UN8RpwWS5TYAY5Nn7

Middle schooler in the mid 90's, sitting in the backseat of the car while parents drove around town on errands. 2 meter ham radio antenna on the roof, with a packet radio modem and black and white power book laptop running off the cigarette lighter jack. The local university had a packet radio - UNIX gateway with which you got a shell prompt via something akin to telnet. Fond memories of wireless browing the web over lynx and talking to people on IRC before anyone I knew had a cellphone.

Also, the special treat of getting to go to the parent's lab from time to time and using this new fangled Netscape Navigator Beta on a blazing fast Macintosh II CI with more than 8 bit color! The fish cam was still one of the featured links on the browser homepage, and browsing NASA's site and being blown away at being able to see monitor-filling celestial objects in seconds.

If you want to live vicariously through others, various people publish live images of captures over their locations on https://wxtoimgrestored.xyz/gallery/ In particular, being on the west coast I'm fond of watching http://wzdave.com/apt/index.html

Also, you don't need a USB SDR per se; the Baofengs will work fine as its just an FM audio signal. The video shows this, but for reference, the three satellites transmitting APT pictures:

https://www.heavens-above.com/SatInfo.aspx?satid=25338&lat=0...

https://www.heavens-above.com/SatInfo.aspx?satid=28654&lat=0...

https://www.heavens-above.com/SatInfo.aspx?satid=33591&lat=0...

As others have mentioned, you don't need a fancy antenna; even a car magnetic mount 2-meter ham radio antenna will work to an extent; the problem and fun part about this is it's wonderfully analong ... any noise in the signal shows up at snow in the picture, and if your antenna isn't circularly polarized, the strength will fade in and out as the satellite moves over the horizon. Still, it works well enough to try out. In fact, even the rubber duck on the Baofeng will kind of work if its a high elevation pass (70-90 degress) as the satellite is closer and has less atmospheric attenuation. A trick I've done in the past is just to record the output of the Baofeng on your phone's voice memo app and play it back later when you're back inside.

Finally, it's worth noting that APT (the tech in this video) is somewhat deprecated, but if you have an SDR already, for somewhat more effort you can receive the digital equivalent https://en.wikipedia.org/wiki/Low-rate_picture_transmission

Edit:

The frequencies NOAA 15 137.62MHz NOAA 18 137.9125MHz NOAA 19 137.10MHz

Also, if you're using a Baofeng, set it to wideband FM in the menu. The APT signal has fairly wide FM modulation compared to most terrestrial voice FM, and even wideband mode won't be enough. It'll still work in any case, but has the effect that the contrast of the picture is somewhat clipped the narrower your receive bandwidth is.

1. You found your call sign already, but if you're interested in upgrading, the https://www.kb6nu.com/study-guides/ were very helpful for me becoming a general which lets you play in the world of HF radio. There are exams in almost everywhere about once a month http://www.arrl.org/find-an-amateur-radio-license-exam-sessi... and they're just multi-choice which aren't too difficult.

2. For me, three things. There are a variety of low-earth orbiting satellites that can be accessed with nothing but a Baofeng and a yagi built with some Romex copper elements, glue, and balsa wood (Google AMSAT FM). There's something awe-inspiring to me being able to talk to people contient wide with just a few watts and < $50s of walkie-talkie gear. Second, even though it's been possible since the 50's, it's still a rush to talk to people across the US or world over shortwave with just a long wire thrown up in the tree. I got started with the http://www.elecraft.com/KX2/kx2.htm although there are certainly more affordable entry paths. Some spare Ethernet cable, the ugly balum http://www.hamuniverse.com/balun.html and a few trees make a surprisngly effective means of communicating on 40 meters without that much power. Third, although ubiquitos cell service has lessend the usefulness, the distributed nature of being able to transmit your position and exchange txt messages with people around the world via APRS https://aprs.fi/ is still amazing to me.

I wonder what signals they actually route out the FMC card. The website doesn't give a lot of information, but it seems like probably just ChipLink which they claim is their serialized TileLink bus protocol. So, you probably wouldn't be able to just plug a low-cost FMC module into the board. But with something like https://www.xilinx.com/products/boards-and-kits/ek-s6-sp605-... for another $500, you could theoretically use the DVI connector to provide a framebuffer, the PCI connector to interface to an NVME drive, and the FPGA to implement the logic of a TileLink endpoint as well as a minimal framebuffer and PCIe root complex.