
Homemade GPS Receiver - sly010
http://www.aholme.co.uk/GPS/Main.htm
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Quanticles
If anyone is interested in GPS, we're looking for a software engineer ready to
learn about it. (Full Time, Austin)

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shubb
Totally off topic but I'm seeing a lot of hiring going on in Texas. What is
going on down there?

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natebleker
Tax incentives, lower cost of living, and pro business local governments are
driving larger companies to relocate headquarters or major research ops to
Texas en-mass.

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toomuchtodo
Please don't take this the wrong way, but Texas is a pretty terrible place to
live:

[http://pastebin.com/Vt6vNgeS](http://pastebin.com/Vt6vNgeS)

[http://web.archive.org/web/20150401050939/https://www.texast...](http://web.archive.org/web/20150401050939/https://www.texastribune.org/2011/02/14/texas-
is-on-the-brink-legislative-study-group-says/)

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bryondowd
Sounds like a great place to live, if you're privileged and don't care about
the environment or the poor.

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CONTRARlAN
Or, perhaps you move there because you care about the environment or the poor,
and that's how change happens.

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toomuchtodo
Gonna need a whole lot more people to move there before any change occurs.

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bainsfather
"The best fix so far was ±1 metres at a very open location using 12
satellites; but accuracy is typically ±5 metres in poorer locations with fewer
satellites."

That seems very good accuracy. The off-the-shelf GPS I have
([https://www.adafruit.com/products/746](https://www.adafruit.com/products/746))
is always >= ±5m, even with 360 degree view of the sky.

(the specs for my GPS claim < 3 meters, and also say "(all GPS technology has
about 3m accuracy)").

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jhayward
That MediaTek chip is capable of better. Do you have WAAS (SBAS) enabled? 5m
is about what you'd expect without the improved orbit/clock/ionosphere
corrections.

It also pays off to use a good antenna, or at least put a ground plane beneath
a mediocre one to block multipath reflections from the surrounding ground
objects.

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bainsfather
I just used the default settings. Didn't know about WAAS - thanks for pointing
me to it.

From reading some forum posts, it seems you have to explicitly enable WAAS -
I'll give that a try and see how much it helps.

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vinhboy
A while back I was interested in building a DIY GPS after watching Lost. I
day-dreamed about being stranded somewhere remote and building myself a GPS
out of spare parts like MacGyver or something.

After finding this article, I realized that would be an impossible task
without an engineering degree.

Has anyone found a more "For Dummies" version of this?

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krapht
I don't know if "For Dummies" is possible for building a GPS system from first
principles.

If you want to really learn by building, I recommend "Fundamentals of GPS
Receivers: A Hardware Approach" by Dan Doberstein, and building the analog GPS
system described in the first few chapters.

If you simply want to play with GPS, I'm sure there are many breakout modules
from Adafruit et al.

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contingencies
_GPS system from first principles._

To be fair, that would probably be navigation by naturally observable
indicators such as the rising or setting sun, shadows over the day, locally /
seasonally reliable stars for your area, and knowledge of local fauna/wave
patterns.

After getting interested in sailing again (after 20 years) last year through
multihull vessels, I started reading about the evolution of multihulls in the
Pacific and then began looking at traditional navigation techniques. Following
that, I was wondering for fun whether it would be possible to plot one's
position given a rough time, rough position guestimate, and perfectly measured
horizonal inclination, lens property and visible to 'the naked eye' star
positions (ie. visible to the naked CCD at evening time = high ISO, noise and
short shutter speed to failitate clarity in rough seas). My conclusion was
yes, it's possible, with sub-GPS accuracy but accuracy which would be good
enough to get you reliably between certain locations in certain seasons even
on a sailboat.

I was surprised to read that some ICBMs allegedly used astronomy and pre-
loaded landform navigation to avoid issues with jamming, and that fat
databases of precise naked-eye type visible star locations are widely
available, indeed so is software for reducing them to identities from an image
input.

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ceequof
The SR-71 had an automated celestial navigation system that could get a lock
in daylight:
[http://en.wikipedia.org/wiki/Lockheed_SR-71_Blackbird#Astro-...](http://en.wikipedia.org/wiki/Lockheed_SR-71_Blackbird#Astro-
Inertial_Navigation_System)

(The big disadvantage is that it can't see through clouds, of course)

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tyho
Didn't it fly above the clouds?

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ceequof
It was a surveillance aircraft, so it would need line of sight with the ground
as well, which might require flying under cloud cover. Also, having a
gyroscope component, I'm guessing that it would need to calibrate while
stationary, on the runway.

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PhantomGremlin
It didn't fly under cloud cover. It flew Mach 3.3, which it couldn't do in
dense air. Also, flying at 80,000 feet makes it much more difficult to shoot
down.

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jevinskie
The author got a lot further than my attempt! [0] I was attempting to make a
Python-based GPS signal generator for later use in testing a pure VHDL/FPGA
(no embedded CPU) receiver.

[0]: [https://github.com/jevinskie/jevps](https://github.com/jevinskie/jevps)

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jkot
I would be bit careful. GPS is military technology and commercial versions
must have limitations, to be non-usable in rockets (max speed, max
altitude...).

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chisleu
Came for this. This allows someone to build GPS-guided missiles, artillery,
etc.

The laws need to be changed, because consumer-programmable things like FPGAs
and SBCs like BBB/RPi have made weaponizing with even commercially-available,
off-the-shelf products super easy.

For instance, building gps-powered drones with thermite self destruct and an
explosive/incendiary payload is fairly straight forward and extremely
dangerous with little ability to investigate the violator. ICBMs and fast-
flying missiles are much harder.

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deutronium
I'm not sure how you think changing laws would protect anyone, anymore than
they currently do?

Sure lots of things can be used for both good/evil.

Personally I think it's a fascinating project.

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chisleu
I'm saying the laws need to be changed because it doesn't protect anyone.
Better to just make it legal and work to protect us in other ways.

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deutronium
Aha sorry, yes definitely. I wanted to get a thermal sensor a while ago and
would have to fill-in paper work to say it wouldn't be used for malicious
purposes (I didn't end up getting it because it was too expensive anyway), I'm
really not sure the idea of such bureaucracy.

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chisleu
I'm convinced Vogons run the government.

