[time-nuts] GPS SDR (was: FE-.5680A trimming resolution)

Attila Kinali attila at kinali.ch
Thu Feb 2 21:36:51 UTC 2012


On Thu, 02 Feb 2012 15:05:49 -0500
"Daniel Schultz" <n8fgv at usa.net> wrote:

> I found this homebrew GPS receiver project recently:
> 
> http://www.holmea.demon.co.uk/GPS/Main.htm
> 
> No custom specialized chips that are unavailable in small quantities, or which
> will go obsolete in a few months. I think the best solution for the open
> source GPS community is to design open source receivers with commodity parts
> that won't be discontinued in the near future, or for which another commodity
> part can be substituted if need be. Maybe somebody can extend this design with
> a 2-bit ADC on the end (not me, too many projects here already...)


This page went over this list a couple of weeks ago. And actually,
i marked it as "use as reference desgin" :-)

Also a very interesting design is the one in [1], which is a mostly
discrete build GPS/GLONASS receiver. The only integrated components
are the PLL, a 10MHz integrated amplifier and a 68k CPU (plus necessary
logic, ram, rom around it).


Desgning a heterodyne receiver like this (actually super heterodyne
as the last "mixing" stage is in software) is "easy". At least today.
electronic components working in the GHz range are available for
a couple of bucks at single quantities like mixers (eg LT5560, ~3USD),
PLLs with integrated VCO's (ADF4350, ~7USD, or LMX2531, ~14USD).
Not to mention ADC's with sampling rates as high as 200Msps for just
16USD (ADC08200). All you have to do is find appropriate devices,
read the data sheet, apply a fair bit of brain and you get a working
design. I know that even a couple of years back, electronic engineers
would have killed for these devices that are available to us.


			Attila Kinali

[1]  http://lea.hamradio.si/~s53mv/navsats/theory.html
-- 
Why does it take years to find the answers to
the questions one should have asked long ago?



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