[time-nuts] GPS SDR

[Attila Kinali]

On Thu, 02 Feb 2012 01:22:07 +0100
Magnus Danielson <magnus at rubidium.dyndns.org> wrote:

> On 01/02/12 19:12, Attila Kinali wrote:

> > I guestimate, that the RF/ADC part would cost somewhere between
> > 100 to 200 USD in parts. The big uncertainty here is the FPGA.
> > I have no clue how much logic space for a GPS SDR would be needed
> > at minimum and how much would be desirable. Hence i have no guess
> > what the FPGA would cost (could be anything from a cheap 20USD
> > FPGA to a 300 USD one).
> 
> That's why you start of with using an Ettus box as a boiler plate. Once 
> you have working code, you can re-target it for a smaller device and 
> situation. You can do dry synthesis towards the new platform without 
> having it as a physical device. The basic design can still be running on 
> that Ettus platform. Come to think of it, I did get a few university 
> point on a 2-week coarse teaching exactly this point, spin on big-ass 
> FPGA machines and then go to target. :) That's... 18 years ago. Time flies.

Well.. i rather thought about doing a scilab model of the gps signals.
Write the VHDL code, use ghdl to see whether it works correctly and
then use one of those web eddition synthesizers to see how much space
it uses. This way i already have working code when i get the hardware,
don't have to buy any Ettus box and can still choose the right FPGA ;-)

 
> Front-end chips is still there. That's how they build these:
> 
> http://ccar.colorado.edu/gnss/
> http://www.sparkfun.com/products/8238
> http://www.sparkfun.com/products/10981
> 
> That will suffice to get you started in the SDR field.

Hmm.. the successor of the chip used there (the SE4150L) seems
to be available in small quantities... That wasn't the case
when i last looked. But it's limited to L1 C/A only and cannot even
be modified for the P(Y) or Galileos E1 signal.

The MAX2769 (mentioned by Tristan Steele) looks better in that
regard. It can be configured to 8MHz BW, which is enough for E1
reception. Probably a degraded L1 P(Y) tracking could be implemented
as well...

			Attila Kinali

-- 
The trouble with you, Shev, is you don't say anything until you've saved
up a whole truckload of damned heavy brick arguments and then you dump
them all out and never look at the bleeding body mangled beneath the heap
		-- Tirin, The Dispossessed, U. Le Guin