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 (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 (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 (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 (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.
