There've been numerous threads on the Gnuradio mailing list about code
to receive GPS using the Ettus Research USRP hardware.  I don't know
whether anyone has actually made it work, but it appears that it's been
the subject of quite a few academic projects.

John

On 2/1/2012 4:28 AM, Attila Kinali wrote:

On Wed, 01 Feb 2012 09:07:23 -0500
John Ackermann N8UR jra@febo.com wrote:

Yes, i know. That's one of the reasons i said it was not too difficult.
But i have yet to see a project that builds a GPS receiver based on
the USRP with complete source. There was the gps-sdr project a few
years back that was quite advanced, but somewhen in time it just disapeared
from the net and was never seen again. All others i've seen sofar
are either functionally incomplete or do not provide the complete source.

Piecing all the code snipets together that are floating around is
probably more work then writing something from scratch. At least
there is enough documentation around. There are nomerous books on
how GPS works and also quite a few specificaly on how to build
GPS receivers. If you have access to IEEE papers, then you have
a huge pool on problems building GPS receivers and how to solve them.

		Attila Kinali

--
Why does it take years to find the answers to
the questions one should have asked long ago?

On Wed, Feb 1, 2012 at 8:19 AM, Attila Kinali attila@kinali.ch wrote:

That is the problem with an academic projects typically something like
this would be part of a Master's theses or a senior project.  and then
the student graduates and was no more interrest in supporting it.

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.

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.  Then with this you build an open
source thunderbolt type device.    An SDR that samples the microwave
RF is going to be un-affordable, even mixing and down converting
microwaves is not so simple as doing the same on HF ham bands.  But
there might be low level GPS chip available for cheap.

guy works until he has a demo of a proof of concept and can say "Hey
look this sort of works and can do simple things" and then others join

--

Chris Albertson
Redondo Beach, California

On Wed, 1 Feb 2012 09:27:30 -0800, Chris Albertson
albertson.chris@gmail.com wrote:

One of the projects did just this but then the integrated circuit or
module that handled the RF and low level functions was discontinued.
For a while they scavenged the hardware from other products that used
it but then those dried up as well.

I believe the best option now would be to find a ubiquitous and well
documented receiver that provides low level access but I suspect they
no longer exist.

Hi

My guess is that the reality of parts sourcing will quickly get us right
back to the "group buy of LEA-6T" topic.

Bob

-----Original Message-----
From: time-nuts-bounces@febo.com [mailto:time-nuts-bounces@febo.com] On
Behalf Of David
Sent: Wednesday, February 01, 2012 12:38 PM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] GPS SDR (was: FE-.5680A trimming resolution)

On Wed, 1 Feb 2012 09:27:30 -0800, Chris Albertson
albertson.chris@gmail.com wrote:

One of the projects did just this but then the integrated circuit or
module that handled the RF and low level functions was discontinued.
For a while they scavenged the hardware from other products that used
it but then those dried up as well.

I believe the best option now would be to find a ubiquitous and well
documented receiver that provides low level access but I suspect they
no longer exist.

time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to
https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.

On Wed, 1 Feb 2012 09:27:30 -0800
Chris Albertson albertson.chris@gmail.com wrote:

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).

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.

It might not be as simple as doing in the HF ham bands (which anyone
who does GHz electronics considers as DC anyways ;-), but it's possible.
Today we have so much electronic that works in the 2.4GHz band that
we have many devices at our disposal. Yes, working with them requires
more than just a bread board and a few wires. You have to design a PCB
(correctly!) and have to have the equipment to solder and test it.

And this is where the real difficulty lies:
The components on the RF side will be all SMD, often in nasty cases
like QFN. Considering that most people do not dare to solder a SOIC
with it's wide 1.27mm pitch, much less TSOP (0.63mm) or QFP (0.5mm),
how would you design a device that can be build by a normal hobbist?

If you say that home soldering is not an option, you have to start
producing them in batches of >100. Anything else will be just too
expensive (think NRE).

		Attila Kinali

--
Why does it take years to find the answers to
the questions one should have asked long ago?

On Wed, 1 Feb 2012 12:43:55 -0500
"Bob Camp" lists@rtty.us wrote:

As i just wrote in reply to Chris Albertson, sourcing is not really
an issue, as long as you don't strive for highly specialized GPS devices.
But you will not get your hands on those anyways ;-)

But nevertheless... any home brew GPS receiver will be more expensive
than comercial timing module. Even if you pay the ultra high single
piece penalty.

That said. I've contacted u-blox, but got a number that is way out of
what i've expected (approx 120CHF). I'm currently trying to get a lower
price.

		Attila Kinali

--
Why does it take years to find the answers to
the questions one should have asked long ago?

On Wed, Feb 1, 2012 at 9:43 AM, Bob Camp lists@rtty.us wrote:

For timing I don't see why an LEA-6T is better then a Oncore or
t-bolt.  You can buy an Oncore UT for about $18 on ebay and new (with
factory warranty) MT types for about $60.  I just got a t-bolt from a
seller in California for $110.

For car navagation the LEA-6 looks much better because t has inputs
for odometer pulses and a turn rate gyro and the LEA-6 can use this
data for position and rate determination in tunnels and urban canyons.

Chris Albertson
Redondo Beach, California

In message 20120201191226.f6273dcef860b157b817ad48@kinali.ch, Attila Kinali w
rites:

but it's possible.

It's not uncommon for mobile phone frontends to span 600MHz-4GHz these
days, so I would expect you could find something that can be used...

--
Poul-Henning Kamp      | UNIX since Zilog Zeus 3.20
phk@FreeBSD.ORG        | TCP/IP since RFC 956
FreeBSD committer      | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.

On Wed, Feb 1, 2012 at 10:18 AM, Attila Kinali attila@kinali.ch wrote:

What is it these u-blox device can do that a cheaper Motorola Oncore
can't?  Depending on the version the Oncore has for 50 to 5 nS
one-sigma error on the timing pulses and can do either 1PPS or 100PPS.
Single unit prices are from $18 to $60 very good documentation is
available.

If the u-blox was somehow much better than a Trimble thunderbolt or
Motorola Oncore MT12T I'd buy one even at the above price.  But
really these older GPSs are already at the single digtit of
nanoseconds level and I don't see room for improvement except....

If the L2 band is also used.  This is the way to get order of
magnitude improments

Chris Albertson
Redondo Beach, California