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Homemade GPS Receiver

holmea.demon.co.uk

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Re: Homemade GPS Receiver

#51

Post by elemeno »

jessaustin wrote: post #45
wglb wrote: post #24

Earlier quoted context omitted.

Oh, likely, but the duplicate detection is based on URL matching, not on newness of content. See the other submission at https://news.ycombinator.com/item?id=5717674 and note that the referenced URL does not have the # at the end that this one does.

How about this one: https://news.ycombinator.com/item?id=5699429 Whatever. I'm glad people are looking at this because it is incredible. EDIT: I do wonder, however, that the link from 3 days ago only has one point, which is what it had as soon as it was created. Presumably elemeno appended the "#" before he submitted the link, because if he had just submitted the link then the 3-day-ago link would have at least two p…

The three days ago one didn't come up when I first put the URL in, though the 500+ days ago one did. Quite possibly I was simply lucky in that I posted near the start of the UK work day, thus making it likely to get noticed by people in Europe and then the US, also quite possibly there's a bit of extra magic in how HN deals with dupes and how quickly it forgets about submissions that get no love.

Re: Homemade GPS Receiver

#52

Post by sounds »

shabble wrote: post #36
fvox13 wrote: post #11

Sure, he designed it, but I don't think those nice printed PCBs are "homemade". I'd be more impressed if it were through-hole construction. Still, it's pretty cool.

What are you, Etsy? :P He didn't fab his own silicon, package his own dies, or even machine his own connectors! The hard (and interesting) parts are the design and testing/debugging phases. Building your own PCB to handle various RF signals at this sort of level is non-trivial in both time and money, and doesn't really gain you much. There's no reason why it should be through-hole either, and indeed, good luck findin…

I do agree, but to be fully pedantic,

  L1 and L2 are hand-wound microwave chokes with
  very high self-resonant frequency, mounted
  perpendicular to one another and clear of the
  ground plane. Wind 14 turns, air-cored, 1mm
  inside diameter from 7cm lengths of 32swg
  enamelled copper wire. Checked with the tracking
  generator on a Marconi 2383 SA, these were good
  to 4 GHz.

Re: Homemade GPS Receiver

#53

Post by jessaustin »

elemeno wrote: post #51
jessaustin wrote: post #45

Earlier quoted context omitted.

How about this one: https://news.ycombinator.com/item?id=5699429 Whatever. I'm glad people are looking at this because it is incredible. EDIT: I do wonder, however, that the link from 3 days ago only has one point, which is what it had as soon as it was created. Presumably elemeno appended the "#" before he submitted the link, because if he had just submitted the link then the 3-day-ago link would have at least two p…

The three days ago one didn't come up when I first put the URL in, though the 500+ days ago one did. Quite possibly I was simply lucky in that I posted near the start of the UK work day, thus making it likely to get noticed by people in Europe and then the US, also quite possibly there's a bit of extra magic in how HN deals with dupes and how quickly it forgets about submissions that get no love.

Very weird! The really old one didn't come up for me. It came up for you, but the 3-day-old one didn't. I would speculate that we're seeing the CAP Theorem in action, except I know I've read that HN is hosted on a single box.

Re: Homemade GPS Receiver

#54

Post by gcb0 »

mikeash wrote: post #30
Toucan wrote: post #26

Earlier quoted context omitted.

Less than 100 years ago, GPS wasn't a nav tool until the mid 90s. Astro nav was the standard right up until then and is still taught to masters today. We have calculators for atmospheric diffraction but the long hand method is still used.

Fun fact, the Boeing 747 features a sextant port for convenient celestial navigation in flight.

http://virginflightdeck.blogspot.com/2010_09_01_archive.html

search for "periscopic sextant"

Re: Homemade GPS Receiver

#55

Post by dfox »

joezydeco wrote: post #12
fvox13 wrote: post #11

Sure, he designed it, but I don't think those nice printed PCBs are "homemade". I'd be more impressed if it were through-hole construction. Still, it's pretty cool.

Doubtful you can get an FPGA of that class in a thru-hole package. The dude was smart to shop out the PCB instead of spending weeks trying screen and drill his own.

You probably can get FPGA in CPGA package that has similar performance to that Spartan3, but these things are meant for high reliability and wide temperature range military/aerospace applications (you get either THT or really funky SMT packages there) and certainly beyond the budget of most hardware companies, not to say any hobbyist.

Re: Homemade GPS Receiver

#56

Post by sbierwagen »

mikeash wrote: post #47
Florin_Andrei wrote: post #39

Earlier quoted context omitted.

Wow. Was it ever used?

Can't find much information about it, but what I did find says that it got significant use in the early years of the 747. It makes sense, as the 747 long predates civilian GPS, and other electronic navigation techniques were not completely reliable for long flights. I don't know that there were many radio beacons available for long over-water flights, and pilots probably liked cross-checking their INS. While searchin…

  that could get still a position fix on the ground in 
  the middle of the day
What! Surely the sky would outshine the stars... did it use light outside of the visual spectrum?

Re: Homemade GPS Receiver

#57

Post by fancyketchup »

mikeash wrote: post #47
Florin_Andrei wrote: post #39

Earlier quoted context omitted.

Wow. Was it ever used?

Can't find much information about it, but what I did find says that it got significant use in the early years of the 747. It makes sense, as the 747 long predates civilian GPS, and other electronic navigation techniques were not completely reliable for long flights. I don't know that there were many radio beacons available for long over-water flights, and pilots probably liked cross-checking their INS. While searchin…

There are some really interesting patents related to this (search for variations on celestial navigation at USPTO or Google Patents). Apparently it is possible to track stars in full daylight using a single photosensitive device behind an IR-pass filter (stars radiate IR, but the atmosphere doesn't scatter significant IR from the sun) and a clever arrangement of shutters. Several of the most interesting patents are refinements to allow the system to work well during dawn and dusk, when the background brightness of the sky varies greatly with elevation above the horizon.

Re: Homemade GPS Receiver

#58

Post by mikeash »

sbierwagen wrote: post #56
mikeash wrote: post #47

Earlier quoted context omitted.

Can't find much information about it, but what I did find says that it got significant use in the early years of the 747. It makes sense, as the 747 long predates civilian GPS, and other electronic navigation techniques were not completely reliable for long flights. I don't know that there were many radio beacons available for long over-water flights, and pilots probably liked cross-checking their INS. While searchin…

that could get still a position fix on the ground in the middle of the day What! Surely the sky would outshine the stars... did it use light outside of the visual spectrum?

Check out fancyketchup's sibling comment to yours, which shows far more knowledge than I have. Short version: infrared.

Re: Homemade GPS Receiver

#59

Post by Florin_Andrei »

sbierwagen wrote: post #56
mikeash wrote: post #47

Earlier quoted context omitted.

Can't find much information about it, but what I did find says that it got significant use in the early years of the 747. It makes sense, as the 747 long predates civilian GPS, and other electronic navigation techniques were not completely reliable for long flights. I don't know that there were many radio beacons available for long over-water flights, and pilots probably liked cross-checking their INS. While searchin…

that could get still a position fix on the ground in the middle of the day What! Surely the sky would outshine the stars... did it use light outside of the visual spectrum?

Jupiter, Venus, Sirius and, at the very limit, even Canopus are visible with the naked eye during the day. It's just hard to "get a lock" on them because contrast is so low. But if they are close to a large, fixed, easily visible reference (the Moon, a tall building, a tree) then suddenly they pop into view. The first two are easy, the third is doable in good conditions, the last is difficult and requires excellent conditions and a keen eye.

You need more than a few stars for navigation, of course, but I would assume with a good sensor, proper filtering, and nice optics, a computer could see enough stars during daytime to perform navigation.

Re: Homemade GPS Receiver

#60

Post by kyle_martin1 »

I'm a software developer gone electrical/computer engineer and this is still a very high-level overview. You need to understand many advance physics topics like RF, antennas design, extremely complicated DSP algorithms, hardware architecture and design for the FPGA, etc. The breadth and deep understanding of very hard topics is VERY different than most web developers/people on here that write toy utilities programs then post a link to Github..
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