[time-nuts] GPS/SDR project design feedback needed
Hi group, Please email any follow-up to me directly, and not to the list, unless it is relevant to the GPS aspect. My little GPS / SDR add-on board project for the BeagleBone Black (GPS front-end + FPGA + ADC) is ready for first PCB fab. But I'd like to get some feedback on the design before I spend money. I'd particularly like to hear from any of you with EMI/EMC, FCC testing or PCB DFM experience. While the software-defined GPS on the board is fun to play around with, and educational if you've ever been curious about the details of a functioning GPS receiver, this board will probably never be the basis of a GPSDO because of the unknown quality of the L1 VCO inside the front-end chip. You can supply a high-quality external 16.368 MHz clock to the VCO PLL, but I don't think that's good enough without knowing the PLL quality. But I don't understand the fine points of GPSDO design, so maybe someone can comment. Live prototype SDR: http://www.jks.com:8073 (password is 'kiwi') Design review document: www.jks.com/docs/wrx/wrx.design.review.pdf (60 pages, which I don't expect anyone to fully read) PCB Gerbers and sources: : https://github.com/jks-prv/Beagle_SDR_GPS History: www.jks.com/wrx/wrx.html Thanks in advance! John ___ 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.
[time-nuts] GPS SDR
I thought this[1] might be of interest to time nuts. It seems that some folks have been working on one obvious application to the new tool presented to us by the rts-sdr project: GPS reception. In addition to some discussion of software implementation, the post has some references to some open source FPGA receivers that might be of use to time nuts. Cheers, - Ben [1] http://michelebavaro.blogspot.it/2012/04/spring-news-in-gnss-and-sdr-domain.html ___ 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.
Re: [time-nuts] GPS SDR
On Fri, 13 Apr 2012 15:45:22 -0400 Ben Gamari bgam...@physics.umass.edu wrote: I thought this[1] might be of interest to time nuts. It seems that some folks have been working on one obvious application to the new tool presented to us by the rts-sdr project: GPS reception. In addition to some discussion of software implementation, the post has some references to some open source FPGA receivers that might be of use to time nuts. Cheers, - Ben [1] http://michelebavaro.blogspot.it/2012/04/spring-news-in-gnss-and-sdr-domain.html ___ 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. Similarly covered, though not as much technical detail: http://hackaday.com/2012/03/20/software-defined-radio-from-a-usb-tv-capture-card/ ___ 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.
Re: [time-nuts] GPS SDR (was: FE-.5680A trimming resolution)
On 02/03/2012 05:30 AM, Jim Lux wrote: On 2/2/12 12:05 PM, Daniel Schultz 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...) Dan Schultz N8FGV I still think that finding appropriate off the shelf parts to make a subharmonic sampler would be a better strategy.. It's all about whether you want IF filters and a mixer+LO or RF filters. I think the amps are the same either way. The problem with the limiter design is that it is captured by CW noise. It's in the literature. Using a few bits reduces the need, but the AGC control loop needs to be there. With sufficient bits it isn't very critical with AGC anymore. Cheers, Magnus ___ 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.
Re: [time-nuts] GPS SDR (was: FE-.5680A trimming resolution)
On Wed, 1 Feb 2012 09:27:30 -0800 Chris Albertson albertson.ch...@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. http://www.sparkfun.com/products/10981 -- Björn ___ 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.
Re: [time-nuts] GPS SDR
On Thu, 02 Feb 2012 01:22:07 +0100 Magnus Danielson mag...@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 ___ 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.
Re: [time-nuts] GPS SDR
On Thu, 2 Feb 2012 11:41:17 +1100 Tristan Steele tristan.ste...@gmail.com wrote: 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. Heh.. I thought about using teh DE0-nano board from terasic for something similar.. but never got around to buy one.. Anyway, I will be happy to share progress as it occurs if anyone is interested? We are, of course, interested :-) 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 ___ 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.
Re: [time-nuts] GPS SDR
On Wed, 01 Feb 2012 21:53:16 -0800 Jim Lux jim...@earthlink.net wrote: You don't need the ADC: you just need a limiter/comparator. Yes, but this degrades sensitivity quite a lot. You don't need insane sampling rates. Think in terms of subharmonic sampling. This requires that you have an ADC that has the anlog bandwidth of the signal. And ADCs with a analog BW in the GHz range are damn expensive and hard to get. Also a problem is to get the sampling frequency right if you want to sample more than one band. Downmixing solves both of these problems at the cost of higher complexity and a bit more noise. Is there a publically-available antenna design that's easy to fabricate, has a stable phase center, covers 1100--1600 MHz, and has a good pattern over this band with low cross-polarization? Even a large choke-ring design would be okay if it's fully specified. I think there are some crossed dipole designs around. What about quad helix? Crossed dipole are narrow band and not easy to build as dual band designs at least at those frequencies. Quad helix needs quite a precision to get the right frequency and dual band designs (stacked helixes) get even more difficult. 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 ___ 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.
Re: [time-nuts] GPS SDR
On 2/2/12 1:28 AM, Attila Kinali wrote: On Wed, 01 Feb 2012 21:53:16 -0800 Jim Luxjim...@earthlink.net wrote: You don't need the ADC: you just need a limiter/comparator. Yes, but this degrades sensitivity quite a lot. You don't need insane sampling rates. Think in terms of subharmonic sampling. This requires that you have an ADC that has the anlog bandwidth of the signal. And ADCs with a analog BW in the GHz range are damn expensive and hard to get. Also a problem is to get the sampling frequency right if you want to sample more than one band. Downmixing solves both of these problems at the cost of higher complexity and a bit more noise. Yes, if you need lots o'bits, but a single bit sampler with wide bandwidth is easy (which is why they do it). It's basically a D-latch at the end of the amplifier/limiter chain. There is a sampling rate around 38-39 MHz that works out nicely for all three bands (actually, any rate in that range probably works..I haven't looked).. It helps that the 3 GPS frequencies are related to a common base. A few minutes work with an Excel spreadsheet trying frequencies will probably find something that works: You want the carrier to alias to about a quarter of the sample rate (so the entire signal is in the sample bandwidth without aliasing), but not exactly in the center (because having some known frequency offset means your Doppler tracking doesn't have to go through zero) 40MHz gives you a sample bandwidth of 20 MHz, so you could probably sample slower, but I think having more samples/chip makes the tracking easier (if nothing else, oversampling is like having more bits in your ADC) Is there a publically-available antenna design that's easy to fabricate, has a stable phase center, covers 1100--1600 MHz, and has a good pattern over this band with low cross-polarization? Even a large choke-ring design would be okay if it's fully specified. I think there are some crossed dipole designs around. What about quad helix? Crossed dipole are narrow band and not easy to build as dual band designs at least at those frequencies. Quad helix needs quite a precision to get the right frequency and dual band designs (stacked helixes) get even more difficult. I suspect that you're right.. the actual antenna may be simple, the design is hard. The antennas we use for multiband look like a crossed dipole on the surface of a hemisphere, but the actual elements are a very odd shape: generally a wide strip, but there are some lumps and bumps in the outline. I'm going to guess that they were designed with some FEM code, and then iterated by hand. If you knew the shapes, it would be pretty easy to build, though: copper foil tape on an appropriate substrate. As you note, precision is important. I'd go hunting through patents assigned to Dorne Margolin. (part of EDO, these days, I think). Or even maybe looking at their datasheets. There's also what they call the helibowl antenna which is some form of helix in a bowl shaped reflector/ground plane. googling that might turn up something. ___ 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.
Re: [time-nuts] GPS SDR
On Thu, 02 Feb 2012 07:49:53 -0800 Jim Lux jim...@earthlink.net wrote: [Limiting / Downmixing converter] Yes, if you need lots o'bits, but a single bit sampler with wide bandwidth is easy (which is why they do it). It's basically a D-latch at the end of the amplifier/limiter chain. Yes, but you lose IIRC about 3dB of performance compared to a 2bit ADC. There is a sampling rate around 38-39 MHz that works out nicely for all three bands (actually, any rate in that range probably works..I haven't looked).. It helps that the 3 GPS frequencies are related to a common base. Only if you sample them seperately. Which requires seperate, sharp filters for all of them. Also something that isn't that easy to do. Also do not forget that Galileo E1 signals have about a 20MHz Bandwidth. The combined E5 frequencies have about 50MHz. I think i've read somewhere that you can get away with 8MHz for the E1 signal. Don't know how the E5 behaves if you limit its bandwith. 40MHz gives you a sample bandwidth of 20 MHz, so you could probably sample slower, but I think having more samples/chip makes the tracking easier (if nothing else, oversampling is like having more bits in your ADC) Yes. [Antennas] Crossed dipole are narrow band and not easy to build as dual band designs at least at those frequencies. Quad helix needs quite a precision to get the right frequency and dual band designs (stacked helixes) get even more difficult. I suspect that you're right.. the actual antenna may be simple, the design is hard. The antennas we use for multiband look like a crossed dipole on the surface of a hemisphere, but the actual elements are a very odd shape: generally a wide strip, but there are some lumps and bumps in the outline. I thought about combining an antenna simulator with a genetic algo to see whether it produces any usable shapes. But i havent had time for this yet (and it's actually way down in my priority list). I'm going to guess that they were designed with some FEM code, and then iterated by hand. If you knew the shapes, it would be pretty easy to build, though: copper foil tape on an appropriate substrate. As you note, precision is important. That's why i said that probably a patch antenna build out of PCBs is the best solution. You can get the copper sheet at 0.1mm precision which would define frequency and polarity properties quite well. The only thing that would have to be done by hand would be the distance from the ground plate. I guestimate that this value is not as critical and that 0.5mm variation should be ok. I'd go hunting through patents assigned to Dorne Margolin. (part of EDO, these days, I think). Or even maybe looking at their datasheets. There's also what they call the helibowl antenna which is some form of helix in a bowl shaped reflector/ground plane. googling that might turn up something. From my understanding of antenna theory (which is very little), these are mostly variations on the directivity characteristic (ie to get a more favorable distribution), but do not change much the frequency characteristics. Ie if you don't have the frequency characteristics right with a straight design, there wont be much chance to get them right with a shaped design. Attila Kinali -- Why does it take years to find the answers to the questions one should have asked long ago? ___ 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.
Re: [time-nuts] GPS SDR (was: FE-.5680A trimming resolution)
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...) Dan Schultz N8FGV 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.
Re: [time-nuts] GPS SDR
Yes, if you need lots o'bits, but a single bit sampler with wide bandwidth is easy (which is why they do it). It's basically a D-latch at the end of the amplifier/limiter chain. Yes, but you lose IIRC about 3dB of performance compared to a 2bit ADC. Only if you get the gain right. A 1-bit ADC does the right thing with any gain. -- These are my opinions, not necessarily my employer's. I hate spam. ___ 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.
Re: [time-nuts] GPS SDR (was: FE-.5680A trimming resolution)
On Thu, 02 Feb 2012 15:05:49 -0500 Daniel Schultz n8...@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? ___ 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.
Re: [time-nuts] GPS SDR
On Thu, 02 Feb 2012 12:15:41 -0800 Hal Murray hmur...@megapathdsl.net wrote: Yes, if you need lots o'bits, but a single bit sampler with wide bandwidth is easy (which is why they do it). It's basically a D-latch at the end of the amplifier/limiter chain. Yes, but you lose IIRC about 3dB of performance compared to a 2bit ADC. Only if you get the gain right. A 1-bit ADC does the right thing with any gain. If and only if you get over the minimal gain level :-) Yes, you dont have problems with too much gain. But, then, he problem with too much gain is that you lose ADC resolution, ie in the worst case reducing your fancy 32bit ADC to a simple 1bit ADC/comparator. Attila Kinali -- Why does it take years to find the answers to the questions one should have asked long ago? ___ 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.
Re: [time-nuts] GPS SDR (was: FE-.5680A trimming resolution)
On 2/2/12 12:05 PM, Daniel Schultz 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...) Dan Schultz N8FGV I still think that finding appropriate off the shelf parts to make a subharmonic sampler would be a better strategy.. It's all about whether you want IF filters and a mixer+LO or RF filters. I think the amps are the same either way. ___ 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.
Re: [time-nuts] GPS SDR
On 2/2/12 9:39 AM, Attila Kinali wrote: On Thu, 02 Feb 2012 07:49:53 -0800 Jim Luxjim...@earthlink.net wrote: [ There is a sampling rate around 38-39 MHz that works out nicely for all three bands (actually, any rate in that range probably works..I haven't looked).. It helps that the 3 GPS frequencies are related to a common base. Only if you sample them seperately. Which requires seperate, sharp filters for all of them. Also something that isn't that easy to do. The filters don't have to be all that sharp. What you typically do is a chain of amp/filter/amp/filter/amp/filter, etc, for about 6 stages. I'll ask around about the filters, but I suspect they're a pretty standard ceramic thing (it's a bit high frequency to be a SAW), and since GPS frequencies are standard it's likely to be a catalog part. Also do not forget that Galileo E1 signals have about a 20MHz Bandwidth. The combined E5 frequencies have about 50MHz. I think i've read somewhere that you can get away with 8MHz for the E1 signal. Don't know how the E5 behaves if you limit its bandwith. yes, that might be tricky [Antennas] That's why i said that probably a patch antenna build out of PCBs is the best solution. You can get the copper sheet at 0.1mm precision which would define frequency and polarity properties quite well. The only thing that would have to be done by hand would be the distance from the ground plate. I guestimate that this value is not as critical and that 0.5mm variation should be ok. I've seen dual band patches that were pretty simple. One was air dielectric, so the interplate spacing was set mostly by the spacers. I'd go hunting through patents assigned to Dorne Margolin. (part of EDO, these days, I think). Or even maybe looking at their datasheets. There's also what they call the helibowl antenna which is some form of helix in a bowl shaped reflector/ground plane. googling that might turn up something. From my understanding of antenna theory (which is very little), these are mostly variations on the directivity characteristic (ie to get a more favorable distribution), but do not change much the frequency characteristics. Ie if you don't have the frequency characteristics right with a straight design, there wont be much chance to get them right with a shaped design. True in some designs.. however, in general fat elements have wider bandwidth. Adding oddball protrusions and notches can flatten out a response quite nicely. ___ 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.
Re: [time-nuts] GPS SDR (was: FE-.5680A trimming resolution)
On Wed, Feb 1, 2012 at 8:19 AM, Attila Kinali att...@kinali.ch wrote: On Wed, 01 Feb 2012 09:07:23 -0500 John Ackermann N8UR j...@febo.com wrote: 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. 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. From my experience the only way projects like this get started is one 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 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? ___ 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. -- Chris Albertson Redondo Beach, California ___ 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.
Re: [time-nuts] GPS SDR (was: FE-.5680A trimming resolution)
On Wed, 1 Feb 2012 09:27:30 -0800, Chris Albertson albertson.ch...@gmail.com wrote: On Wed, Feb 1, 2012 at 8:19 AM, Attila Kinali att...@kinali.ch wrote: On Wed, 01 Feb 2012 09:07:23 -0500 John Ackermann N8UR j...@febo.com wrote: 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. 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. 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.
Re: [time-nuts] GPS SDR (was: FE-.5680A trimming resolution)
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-boun...@febo.com [mailto:time-nuts-boun...@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.ch...@gmail.com wrote: On Wed, Feb 1, 2012 at 8:19 AM, Attila Kinali att...@kinali.ch wrote: On Wed, 01 Feb 2012 09:07:23 -0500 John Ackermann N8UR j...@febo.com wrote: 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. 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. 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. ___ 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.
Re: [time-nuts] GPS SDR (was: FE-.5680A trimming resolution)
On Wed, 1 Feb 2012 09:27:30 -0800 Chris Albertson albertson.ch...@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). 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. 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. 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? ___ 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.
Re: [time-nuts] GPS SDR (was: FE-.5680A trimming resolution)
On Wed, 1 Feb 2012 12:43:55 -0500 Bob Camp li...@rtty.us wrote: My guess is that the reality of parts sourcing will quickly get us right back to the group buy of LEA-6T topic. 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? ___ 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.
Re: [time-nuts] GPS SDR (was: FE-.5680A trimming resolution)
On Wed, Feb 1, 2012 at 9:43 AM, Bob Camp li...@rtty.us wrote: Hi My guess is that the reality of parts sourcing will quickly get us right back to the group buy of LEA-6T topic. 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 ___ 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.
Re: [time-nuts] GPS SDR (was: FE-.5680A trimming resolution)
In message 20120201191226.f6273dcef860b157b817a...@kinali.ch, Attila Kinali w rites: 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. 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 p...@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. ___ 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.
Re: [time-nuts] GPS SDR (was: FE-.5680A trimming resolution)
On Wed, Feb 1, 2012 at 10:18 AM, Attila Kinali att...@kinali.ch wrote: 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. 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 ___ 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.
Re: [time-nuts] GPS SDR (was: FE-.5680A trimming resolution)
That is also what I like to understand, and when combined with a FE 5680A the time will be long and should be averaged over 100 if not 1000 samples, what is the advantage? Look at the error budget. Bert Kehren In a message dated 2/1/2012 2:04:04 P.M. Eastern Standard Time, albertson.ch...@gmail.com writes: On Wed, Feb 1, 2012 at 10:18 AM, Attila Kinali att...@kinali.ch wrote: 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. 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 ___ 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. ___ 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.
Re: [time-nuts] GPS SDR (was: FE-.5680A trimming resolution)
Chris, When you're down at the ns level, every ns counts even more. There actually a huge difference between a UT and VP and M12 and ... Then again, it's not always about nanoseconds. There are also issues of power and size, support, supply, price, the future. Perhaps also RF sensitivity, feature set, upgrade path for the likes of GLONASS or Galileo, acquisition time. Even RoHS. Perhaps this doesn't matter for a one-off hobbyist, but if you're making kits or products it can become an important factor. If you are inclined to experiment, just for the sake of exploring as many of us on the list are, then certainly you'd want to get a u-blox at some point. It doesn't have to be right away, but it is a pretty nice, very modern, ultra compact, timing receiver. If low cost is the object it's hard to beat that MG1613S board. /tvb 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 ___ 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.
Re: [time-nuts] GPS SDR (was: FE-.5680A trimming resolution)
I think, a specialized GPS SDR can be build for less than 500 USD in low (a dozen at max) volumes. The USRP works for GPS L1 (though P/Y is a little undersampled at 8 Ms/s complex), but I didn't find a way to acquire both L1 and L2 simultaneously at useful sample rates (maybe current USRP hardware is better). Also 16 or 8 bits is too much precision---2 bits is more appropriate and for some reason wasn't a standard option. It was fun to acquire and track L1 and L2C separately, but what I really want is a no-holds-barred geodetic reference receiver. A dedicated tri-band GPS front end could be built for less than $500, I agree. Software can handle acquisition, tracking, and conversion to RINEX. The hardware just needs to translate RF to bits on the wire (gigabit Ethernet say) and be phase-stable over temperature. One possible inexpensive design: - RF input passively split three ways, with LC filters for the three channels: L5/E5, L2, and L1/E1/Glonass - For each channel, a downconverter (Maxim MAX2121) feeding a ~65 Ms/s ADC (e.g. MAX19505) - A low-cost FPGA (e.g. Spartan-6) that quantizes the channels to 2 bits, does AGC, assembles Ethernet packets - Ethernet PHY, power (PoE?), etc. For a timing receiver, one could inexpensively add one more ADC that samples a 10 MHz input signal and a 1PPS input signal. 1PPS packets would be emitted only when transitions are detected, and the 10 MHz signal could be downconverted to a low-bandwidth signal to be sent over Ethernet with the others. This way one has reference signals coherently sampled with the GPS signals. I think LC filters would provide enough protection against strong out-of-band interferers; semicustom ceramic-resonator filters or, worse, full-custom SAW filters are not hobbyist-friendly and may not be as stable over temp. Also I think the phase noise of the MAX2121 is acceptable. Possibly the FPGA should be doing the pulse blanking for L5 since the FPGA still has the 8-bit signal available. Is there a publically-available antenna design that's easy to fabricate, has a stable phase center, covers 1100--1600 MHz, and has a good pattern over this band with low cross-polarization? Even a large choke-ring design would be okay if it's fully specified. Cheers, Peter ___ 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.
Re: [time-nuts] GPS SDR (was: FE-.5680A trimming resolution)
On Wed, 1 Feb 2012 11:03:19 -0800 Chris Albertson albertson.ch...@gmail.com wrote: On Wed, Feb 1, 2012 at 10:18 AM, Attila Kinali att...@kinali.ch wrote: 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. 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. The Timing Appnote [1] says, that the 1PPS error's sigma is 6.7ns, before sawtooth correction and 3.0ns after. If the u-blox was somehow much better than a Trimble thunderbolt or I dont have the numbers, but I doubt that a LEA-6T can beat a thunderbolt. 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 They are not dual band receivers. Yes, that would be really an improvement.. But i'm not convincing you to buy a LEA-6T. Nor do i think that it's a must have for anyone. Heck, you can get a complete thunderbolt with supply and antenna for 200USD on ebay. No LEA-6T based system will ever get that cheap. But there is not much way to tinker with a thunderbolt. You cannot play with its design. If you build a system from scratch, you can. Attila Kinali [1] https://www.u-blox.com/images/downloads/Product_Docs/Timing_AppNote_%28GPS.G6-X-11007%29.pdf -- Why does it take years to find the answers to the questions one should have asked long ago? ___ 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.
Re: [time-nuts] GPS SDR (was: FE-.5680A trimming resolution)
Simple: the ublox will just work when you apply power and have a good antenna. The Motorola units have all sorts of idiosyncrasies, such as sometimes taking a very long time to achieve a lock, having the Almanac get corrupted and not lock when the battery backup is getting low, having significantly lower signal sensitivity (every dB can make a massive quality difference when running in challenged environments such as indoor receiption), and the uBlox are less expensive and support NMEA without having to send binary commands to the unit, and ordering a non-timing version of the GPS. The M12M timing versions do not support NMEA at all. The uBlox also solders down onto a PCB (simpler mounting) and is smaller. Lastly uBlox supports WAAS, which Motorola does not, and they achieve an initial lock much faster than M12M due to their massive parallel correlators. Shall we not forget that some uBlox units will support Gallileo with a firmware upgrade, and will also be able to be ordered with Glonass capability, and have a USB port built-in, and achieve pretty good timing performance in mobile applications that the M12M doesn't handle too well. That said the Motorola M12M or M12+ still have the best timing performance by far of the entire lot when operating, and operated correctly and in stationary mode. So in short: if you need the best timing performance and can fiddle with the GPS to make it work and do not need any bells and whistles, then get an M12M. If you need the easiest to use and fool-proof GPS: get uBlox. bye, Said In a message dated 2/1/2012 11:48:00 Pacific Standard Time, t...@leapsecond.com writes: Perhaps this doesn't matter for a one-off hobbyist, but if you're making kits or products it can become an important factor. If you are inclined to experiment, just for the sake of exploring as many of us on the list are, then certainly you'd want to get a u-blox at some point. It doesn't have to be right away, but it is a pretty nice, very modern, ultra compact, timing receiver. If low cost is the object it's hard to beat that MG1613S board. /tvb 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 ___ 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.
Re: [time-nuts] GPS SDR (was: FE-.5680A trimming resolution)
On Wed, 1 Feb 2012 11:49:51 -0800 Peter Monta pmo...@gmail.com wrote: One possible inexpensive design: - RF input passively split three ways, with LC filters for the three channels: L5/E5, L2, and L1/E1/Glonass - For each channel, a downconverter (Maxim MAX2121) feeding a ~65 Ms/s ADC (e.g. MAX19505) - A low-cost FPGA (e.g. Spartan-6) that quantizes the channels to 2 bits, does AGC, assembles Ethernet packets - Ethernet PHY, power (PoE?), etc. Heh..That's pretty much the design i thought of, though using a higher sampling frequency (100 to 200Msps) which would allow to coherently decode the E5a and E5b signals together. There is an ADC from National that can do 200Msps for 20 bucks, with FPGA friendly parallel output (ADC08200). Is there a publically-available antenna design that's easy to fabricate, has a stable phase center, covers 1100--1600 MHz, and has a good pattern over this band with low cross-polarization? Even a large choke-ring design would be okay if it's fully specified. That's a good question. I don't know. I think a dual band patch antenna design would work (two stacked patches). This would be easy to fabricate with very good horizontal tolerances (just use PCBs). But i have neither designed such an antenna, simulated or even build and tested... But the other designs i've seen are much more difficult to build with home tools or need tuning which is not easily done if you don't have access to good equipment. Attila Kinali -- Why does it take years to find the answers to the questions one should have asked long ago? ___ 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.
Re: [time-nuts] GPS SDR (was: FE-.5680A trimming resolution)
Can I ask where does the Trimble Resolution-T fit between this other receivers ? I've used it and I do like it. I thought it was relatively modern and capable compared to the Oncore. Isn't it comparable to the uBlox for example? Regards, Roberto EB4EQA From: albertson.ch...@gmail.com Date: Wed, 1 Feb 2012 10:38:25 -0800 To: time-nuts@febo.com Subject: Re: [time-nuts] GPS SDR (was: FE-.5680A trimming resolution) On Wed, Feb 1, 2012 at 9:43 AM, Bob Camp li...@rtty.us wrote: Hi My guess is that the reality of parts sourcing will quickly get us right back to the group buy of LEA-6T topic. 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 ___ 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. ___ 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.
Re: [time-nuts] GPS SDR (was: FE-.5680A trimming resolution)
Being divorced and no children writing a large check is neither a problem nor a challenge. To me the challenge is to find solutions that are affordable and work for every body. Sadly there is very little interest or emphasis in this group on this. An example the $ 10 Loran C simulator that Paul and I build and tested, turning obsolete Loran C Receivers in to high resolution frequency displays. Many other projects off list. The way I understand it the discussion on GPS receivers, in this thread started looking for a solution for the FE 5680A. To look at the proper configuration, first there has to be a good understanding of the Rb. Aging will determine the update rate of the Rb. Second the choice has to be made if digital or analog frequency control will be implemented. Digital dither or no dither. With out dither we are talking 3 E-13 setability. Enough? Some one has to test how the Rb reacts to dither. Right now I se a 4 to 5 Hz control loop in my tests. Analog 1 E -14 is no problem. With aging and step requirement a loop can be defined. Being Rb, it can be a long loop which will reduce requirements of the GPS receiver and most likely issues like ionospheric delays will play a roll. That is the time to ask the question what does the GPS receiver have to be. All the other chatter should be part of a different thread because it may confuse some of the readers. How many FPGA's are running and can be copied by members? Many have bought FE 5680 A and have no idea how their individual unit performs. I have seen 8 E-10 off frequency. Bert Kehren In a message dated 2/1/2012 2:47:51 P.M. Eastern Standard Time, t...@leapsecond.com writes: Chris, When you're down at the ns level, every ns counts even more. There actually a huge difference between a UT and VP and M12 and ... Then again, it's not always about nanoseconds. There are also issues of power and size, support, supply, price, the future. Perhaps also RF sensitivity, feature set, upgrade path for the likes of GLONASS or Galileo, acquisition time. Even RoHS. Perhaps this doesn't matter for a one-off hobbyist, but if you're making kits or products it can become an important factor. If you are inclined to experiment, just for the sake of exploring as many of us on the list are, then certainly you'd want to get a u-blox at some point. It doesn't have to be right away, but it is a pretty nice, very modern, ultra compact, timing receiver. If low cost is the object it's hard to beat that MG1613S board. /tvb 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 ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/ma ilman/listinfo/time-nuts and follow the instructions there. ___ 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.
Re: [time-nuts] GPS SDR
On 01/02/12 19:12, Attila Kinali wrote: On Wed, 1 Feb 2012 09:27:30 -0800 Chris Albertsonalbertson.ch...@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 ___ 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.
Re: [time-nuts] GPS SDR
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 interested? Cheers for Oz, Tristan (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 mag...@rubidium.dyndns.orgwrote: On 01/02/12 19:12, Attila Kinali wrote: On Wed, 1 Feb 2012 09:27:30 -0800 Chris Albertsonalbertson.chris@**gmail.com albertson.ch...@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/8238http://www.sparkfun.com/products/8238 http://www.sparkfun.com/**products/10981http://www.sparkfun.com/products/10981 That will suffice to get you started in the SDR field. Cheers, Magnus __**_ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/** mailman/listinfo/time-nutshttps://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ 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.
Re: [time-nuts] GPS SDR
On 2/1/12 9:27 AM, Chris Albertson wrote: On Wed, Feb 1, 2012 at 8:19 AM, Attila Kinaliatt...@kinali.ch wrote: On Wed, 01 Feb 2012 09:07:23 -0500 John Ackermann N8URj...@febo.com wrote: 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. 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. Actually, most of the JPL GPS receivers do direct sampling from RF with a single bit converter. You need about 100dB of gain from the antenna, with some filtering (to get L1 by itself), and then you run it into a limiter, and just sample the output at around 40 MHz, run it into an FPGA, and do your stuff. No superhet, no mixers, no nothing. It's only 1.5 GHz.. these days, that's not particularly exotic. http://trs-new.jpl.nasa.gov/dspace/bitstream/2014/41781/1/11-0046.pdf gives some hints on the hardware side. From my experience the only way projects like this get started is one 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 Yep ___ 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.
Re: [time-nuts] GPS SDR
On 2/1/12 10:12 AM, Attila Kinali wrote: On Wed, 1 Feb 2012 09:27:30 -0800 Chris Albertsonalbertson.ch...@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). how many channels do you want to track at once? I can tell you that you can track at least 12 channels simultaneously with single bit ADC sampling at around 40 MHz in a pair of Virtex II 3000 parts. You might be able to do better (I don't know how full the two FPGAs are). (that's the published spec for the radio we're flying on the SCAN Testbed on ISS) It's actually a L1,L2,L5 receiver, but, of course, the tracking loop is the same for all frequencies, whether you track 12 S/Vs in L1 or 4 in all three channels.. it's all the same. You'll have to do the nav solution in some sort of other processor.. that's just running the tracking loops and generating raw observables. ___ 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.
Re: [time-nuts] GPS SDR
On 2/1/12 12:22 PM, Attila Kinali wrote: On Wed, 1 Feb 2012 11:49:51 -0800 Peter Montapmo...@gmail.com wrote: One possible inexpensive design: - RF input passively split three ways, with LC filters for the three channels: L5/E5, L2, and L1/E1/Glonass - For each channel, a downconverter (Maxim MAX2121) feeding a ~65 Ms/s ADC (e.g. MAX19505) - A low-cost FPGA (e.g. Spartan-6) that quantizes the channels to 2 bits, does AGC, assembles Ethernet packets - Ethernet PHY, power (PoE?), etc. You don't need the ADC: you just need a limiter/comparator. But you do need a bunch of RF gain. I think you can get suitable ceramic filters off the shelf for the GPS frequencies that are inexpensive. You don't need insane sampling rates. Think in terms of subharmonic sampling. Heh..That's pretty much the design i thought of, though using a higher sampling frequency (100 to 200Msps) which would allow to coherently decode the E5a and E5b signals together. There is an ADC from National that can do 200Msps for 20 bucks, with FPGA friendly parallel output (ADC08200). Is there a publically-available antenna design that's easy to fabricate, has a stable phase center, covers 1100--1600 MHz, and has a good pattern over this band with low cross-polarization? Even a large choke-ring design would be okay if it's fully specified. I think there are some crossed dipole designs around. What about quad helix? ___ 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.
