[time-nuts] GPS SDR

[Magnus Danielson]

On 01/02/12 19:12, Attila Kinali wrote:
> On Wed, 1 Feb 2012 09:27:30 -0800
> Chris Albertson<albertson.chris at gmail.com>  wrote:
>
>> I thought it might be interresting but then found out you need to buy
>> $2,000+ worth of hardware for even start experimenting.    Open Source
>> SDR needs to run on a common affordable platform or it will never gain
>> the critical mass of users that it take to make the project live
>> longer then a few months.
>
> That's because the URSP is a general purpose system. It is designed
> to do many things. That makes it expensive. And being expensive,
> it has a low production volume, which makes it even more expensive.
>
> I think, a specialized GPS SDR can be build for less than 500 USD
> in low (a dozen at max) volumes.
>
> 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.

>> I think the way to go is to find a commercial GPS chip that has a low
>> level interface and then build the uP controller using a common
>> development system.   Both the chip and the uP board need to be,
>> common, well documented and cheap.
>
> There are no common, well documented and cheap GPS frontend chips
> out there. All chips that are still in production are for high volume
> stuff. Without knowing someone inside those companies, you will not
> be able to get them at single pieces. I searched quite a while some
> time ago, and couldn't find anything that is not EOL. Finally i came
> to the conclusion that it is easier to build a custom frontend from
> scratch, from the available HF parts.

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.

Cheers,
Magnus