Homemade GPS Receiver

http://www.holmea.demon.co.uk/GPS/Main.htm

by samlittlewood • 15 years ago

329 13 15 years ago

holmea.demon.co.uk

Really cool project, seeing hackers who really understand the technology makes for great reading! Thanks for sharing this!

VladRussian• 15 years ago

great combination of electrical engineering, core physics (classical and if you want it - GPS does touch SR and GR), programming (at app and VSDL levels). Such projects should be a regular part of lab curriculum for any engineering student (including programmers).

samlittlewood• 15 years ago

Also, this article references an older project that has (for me) the clearest description of the theory of GPS:

http://lea.hamradio.si/~s53mv/navsats/theory.html

caf2• 15 years ago

Cold start to lock in 2.5 seconds is pretty damn good.

moe• 15 years ago

It's an order of magnitude better than my Samsung Galaxy S can do (when it gets a lock at all...).

caf2• 15 years ago

Yes - it's because of the clever design that means that it doesn't use the Almanac data, so it doesn't need to wait for it to download.

jgrahamc• 15 years ago

I guess this is what it takes to get round the CoCom limit: http://blog.jgc.org/2010/11/gaga-1-cocom-limit-for-gps.html

calloc• 15 years ago

Having done two balloon launches, it is not that hard to find resources that specify what GPS modules will work and what ones won't work.

We used a

Garmin GPS 18

and it worked flawlessly (other than our night launch, where we recorded really low freezing temperatures and we think that our GPS froze because it stopped giving us data).

Our first launch got to 92k+ ft and the GPS kept reporting without issues.

jeremyarussell• 15 years ago

Thought this was great, will be trying to make one myself I think. Keep up the awesome work, I'm keeping your site bookmarked now. (I saw a whole bunch of other cool stuff.)

spitfire• 15 years ago

I wish I could upvote this several times over. This is hacker news a thousand times over, and makes up for all the dotcom, and ruby rubbish you have to wade through on this site.

Well done sir.

Create• 15 years ago

What I cannot create, I do not understand -- as quoted in The Universe in a Nutshell, Richard Feynman

The scientist describes what is; the engineer creates what never was. -- Kármán Tódor

joshu• 15 years ago

An absolute rockstar.

zb• 15 years ago

The L1 carrier is spread over a 2 MHz bandwidth and its strength at the Earth's surface is -130 dBm. Thermal noise power in the same bandwidth is -111 dBm, so a GPS signal at the receiving antenna is ~ 20 dB below the noise floor.

This is slightly misleading; the bandwidth of the entire signal is 2MHz (it's a 1MHz chip). The bandwidth of the carrier is much narrower - it is above the noise floor typically by somewhere between about 15 and 50dBHz (you can see this quite easily on a spectrum analyser). The spread-spectrum part of the signal is indeed well below the noise floor.

That minor quibble aside, this is a pretty awesome effort for one guy to do end-to-end.

Homemade GPS Receiver

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