[time-nuts] GPS SDR

Tristan Steele tristan.steele at gmail.com
Thu Feb 2 00:41:17 UTC 2012

Hi All,

I've been lurking here for a while, learning lots - but I think I may be
able to contribute something to this discussion.

I have been looking at SDR GPS reception for a while, and have a number of
ideas as to how to go about this process.  My first point of call is the
layout of a board using a MAX2769B (1) receiver chip attached directly to a
Spartan 3E- 500 FPGA and then to a USB interface.  I have decided to do
this using an add-on board to the Papillio FPGA boards (2) that have been
linked here before, incorporating the receiver chip, level shifters, power
supplies, as well as a somewhat buffered SMA input for monitoring an
external signal.  The original board design requires an external reference
oscillator for the MAX2769B, I am intending to operate it with a 10MHz
signal to begin with.

In addition to the above, the board also features an FTDI FT2232H (3)
device for USB data streaming, in addition to the 2232D chip on the
Papillio board used for programming.  This should be able to handle
streaming the data from the 2769B chip, at least for some initial testing
and proof of concept.

As for progress, there is a small amount of routing to be finished and I am
intending to submit the board for manufacture in the next few days. It is
mainly a learning experience so far, but the general aim is to have
something similar to the GNSS Sampler boards for a smaller price (and
hopefully not a fraction of the performance!).

Anyway, I will be happy to share progress as it occurs if anyone is

Cheers for Oz,

(1)  - www.maxim-ic.com/datasheet/index.mvp/id/7267
(2) -   http://papilio.gadgetfactory.net/
(3) - www.ftdichip.com/Products/ICs/FT2232H.htm

On 2 February 2012 11:22, Magnus Danielson <magnus at rubidium.dyndns.org>wrote:

> On 01/02/12 19:12, Attila Kinali wrote:
>> On Wed, 1 Feb 2012 09:27:30 -0800
>> Chris Albertson<albertson.chris@**gmail.com <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/8238>
> http://www.sparkfun.com/**products/10981<http://www.sparkfun.com/products/10981>
> That will suffice to get you started in the SDR field.
> Cheers,
> Magnus
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