[time-nuts] GPS Timing receivers
Hi everybody, I'm a final year student in TLC engineering, from the Polytechnic of Turin. The subject of my thesis is the GPS Timing Receivers in general. My main interests are: 1) Evalutation of GPS receivers performances, therefore I'm interested in test procedures. In this connection I've read the articles about the Test Bed at USNO in order to evaluate the M12+. My questions are: - it is correct to evaluate a gps timing receiver just on the basis of their 1pps? - it is possible to test a 1PPS using a TIC without a reference clock? - can you suggest me material (articles, proceedings and so on) about this kind of tests. 2) Timing Receivers architectures: I'm mainly interested in understanding how the 1pps is generated within the receiver. I've read a lot of IEEE docs, patents, manuals and application notes, but I haven't understood yet some details (maybe they are proprietary information!). Could you indicate to me any material that can be useful to my research? I hope to find some experts in that field, with whom to exchange opinions and experiences. I'm sorry for my poor English. Thank you very much. Kind regards, Albertazzi Michelangelo. ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
Re: [time-nuts] GPS Timing receivers
Hi everybody, I'm a final year student in TLC engineering, from the Polytechnic of Turin. The subject of my thesis is the GPS Timing Receivers in general. Congratulations. My main interests are: 1) Evalutation of GPS receivers performances, therefore I'm interested in test procedures. In this connection I've read the articles about the Test Bed at USNO in order to evaluate the M12+. Yes, that's a good one. My questions are: - it is correct to evaluate a gps timing receiver just on the basis of their 1pps? It depends very much on the application. Sometimes evaluations include things like weight, size, power requirements, acquisition time, price, TRAIM quality, temperature coefficient, etc. But plain 1PPS is a good start since it is the key feature that distinguishes a GPS timing receiver from a normal GPS receiver. Then there are a host of issues with evaluating antennas, which although not part of the GPS receiver, can be important to the quality of the 1PPS you are measuring. - it is possible to test a 1PPS using a TIC without a reference clock? - can you suggest me material (articles, proceedings and so on) about this kind of tests. I think you need a reference. But for most 1PPS analysis a rubidium standard and a 1 ns TIC is sufficient. There are several ways to quantify the 1PPS signal. Almost all manufacturers specify things like signal rise time and jitter (sawtooth). But in some applications the actual accuracy of the 1PPS signal is what is important. That's what Rick was measuring at USNO. You could probably do the same with the help of a calibrated tick at IEN in Turin. In this case the antenna, cable(s), connector(s), etc. all have an effect on the final result. 2) Timing Receivers architectures: I'm mainly interested in understanding how the 1pps is generated within the receiver. I've read a lot of IEEE docs, patents, manuals and application This is further complicated since there are many different receiver architectures and methods to recover the timing. Look for subjects like single vs. dual frequency (L1/L2), code vs. carrier phase, real-time vs. post processed, precise orbits, all in view vs. common view, etc. notes, but I haven't understood yet some details (maybe they are proprietary information!). Could you indicate to me any material that can be useful to my research? If anyone finds some good articles let me know too! I hope to find some experts in that field, with whom to exchange opinions and experiences. I'm sorry for my poor English. Thank you very much. Kind regards, Albertazzi Michelangelo. /tvb http://www.LeapSecond.com/time-nuts.htm ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
Re: [time-nuts] GPS Timing receivers
From: Tom Van Baak [EMAIL PROTECTED] Subject: Re: [time-nuts] GPS Timing receivers Date: Thu, 6 Oct 2005 14:29:58 -0700 Message-ID: [EMAIL PROTECTED] Hi everybody, I'm a final year student in TLC engineering, from the Polytechnic of Turin. The subject of my thesis is the GPS Timing Receivers in general. Congratulations. My main interests are: 1) Evalutation of GPS receivers performances, therefore I'm interested in test procedures. In this connection I've read the articles about the Test Bed at USNO in order to evaluate the M12+. Yes, that's a good one. My questions are: - it is correct to evaluate a gps timing receiver just on the basis of their 1pps? It depends very much on the application. Sometimes evaluations include things like weight, size, power requirements, acquisition time, price, TRAIM quality, temperature coefficient, etc. But plain 1PPS is a good start since it is the key feature that distinguishes a GPS timing receiver from a normal GPS receiver. I agree. There are *many* different issues to consider, but assuming that other operating conditions is fair, good or even optimum, the PPS will be a good place to start. Then there are a host of issues with evaluating antennas, which although not part of the GPS receiver, can be important to the quality of the 1PPS you are measuring. - it is possible to test a 1PPS using a TIC without a reference clock? - can you suggest me material (articles, proceedings and so on) about this kind of tests. I think you need a reference. But for most 1PPS analysis a rubidium standard and a 1 ns TIC is sufficient. You don't need a timing reference per se, but it simplifies the analysis alot. You can compare the signal against itself using either a delayline or by using the TIC timebase as your resolving time delay. For both solutions the result will depend on the stability of the delay or the time base for the region of interest. For longer measurement times, having a good reference signal is really the best solution in reality, unless you find a stable delay you can count on. 2) Timing Receivers architectures: I'm mainly interested in understanding how the 1pps is generated within the receiver. I've read a lot of IEEE docs, patents, manuals and application This is further complicated since there are many different receiver architectures and methods to recover the timing. Look for subjects like single vs. dual frequency (L1/L2), code vs. carrier phase, real-time vs. post processed, precise orbits, all in view vs. common view, etc. Indeed. notes, but I haven't understood yet some details (maybe they are proprietary information!). Could you indicate to me any material that can be useful to my research? If anyone finds some good articles let me know too! Well, the first book I should recommend is really Understanding GPS - Principles and Applications with Elliott D. Kaplan as editor. Read it. This is not the authorative text on all aspects (I can give further reading tips which is) but it gives a very good and actually quite advanced level of GPS knowledge in the size there is. Now, in there (to tired to dig up the detailed reference position) is the description of how the PPS is generated and really from what basis in the solution. I think one should not really dig into the more advanced material until one have read this book fairly thorowly, it is well spent time, since things intertangle in an intricate dance which at first takes some time to apprechiate even if one has got the initial overview message. Even if I have more advanced texts, I find that I use this one as a basic reference for a quick refresh on the basics. However, to come back to your problem. What the GPS receiver do is really measure the phase state of the signal as received from a number of satelites at its (or actually, the antennas) position. The carrier phase is tracked in a loop, the C/A or P code is tracked in a code loop and the 50 bps message code helps to create a channel for additional information as well as system time for the GPS signal as it was transmitted from the satellite. We can then cancel out the three unknowns in the physical position and the unknown in the local time offset. Since we correlate the measurements to the local clock, we can now use the time-position given to correct time such that the timing reference internal to the node tracks the GPS system. From this it is trivial to have a corrected PPS generated. This is the big wavey arm kind of description, there is more in the book, but in the end there is not very much magic in it. You have a clock phase which is running and you correct its frequency and phase to align. It is samples in the hardware receiver so we can correlate the system time with the received signal. The GPS solution gives the errors and we correct from that. Cheers, Magnus ___ time-nuts mailing list
Re: [time-nuts] GPS Timing receivers
Tom, John A and I had a short antenna email earlier today, mostly about the fact that both of the GPS antennas we were using died. I asked a question about certain commercial antennas which included the Timing 2000, HP 58532A and the Datum 2640NW/DE, as to wether there were any opinions as to which is the better timing antenna. Neither of us has much of an idea, do you have any thoughts? Had I've heard that many modern telecom GPS timing antennas are heavily filtered since they are usually placed in high RFI locations. This may be good for them but I think it has negative side effects for the kind of precise timing we do, so I'm told. I'm going to ask Dr Clark to handle this one as he understands GPS antennas very well. TAC -- what I'd like to know is if patch is better than helix, if filtered is better than unfiltered, how much amplification is too much, vintage 1990's era antennas vs. 2005 antennas, real splitters vs. Radio Shack splitters, antenna or preamp tempco issues, cable loss and impedance issues, etc. At what ns level does a groundplane start to matter. I guess what we need is some kind of Time Nuts guide to surplus GPS antennas. If it's not possible to give a black and white answer to what kind of antenna is best for a Z3801A-style GPSDO, then at least, what are the factors that make one better than another. And is any of this simple to determine with experimentation? Maybe we can all chip in and test a dozen antenna types to find the answer or to confirm a prediction. /tvb ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
Re: [time-nuts] GPS Timing receivers
Hi Tom: When I was learning about the Trimble 1990 vintage Trimpack family of receivers I bought a number of antennas and learned that the Trimpacks need an antenna with about 40 dB of gain, which is a lot different from a passive antenna or an active antenna with the more common 20 dB of gain. http://www.pacificsites.com/~brooke/Trimpack.shtml#Ant A passive antenna is good for use as a re-radiating antenna for indoor GPS. I'm using a Motorola Timing antenna on a TV mast to get it above the chimney closest to my radio room. But in order to get rid of the multipath I've had to move the elevation mask up to the 50 or 60 degree level. At lower elevation levels the standard deviation on TI measurements gets much higher. I think that if a choke ring type antenna was in the same position I could lower the elevation mask and receive more satellites, thus enabling TRAIM, or getting better 1 PPS signals. But the choke ring antennas are larger than the Timing antenna and are not easily mounted to a TV antenna type mast (they want to see pipe threads). Have Fun, Brooke Tom Van Baak wrote: Tom, John A and I had a short antenna email earlier today, mostly about the fact that both of the GPS antennas we were using died. I asked a question about certain commercial antennas which included the Timing 2000, HP 58532A and the Datum 2640NW/DE, as to wether there were any opinions as to which is the better timing antenna. Neither of us has much of an idea, do you have any thoughts? Had I've heard that many modern telecom GPS timing antennas are heavily filtered since they are usually placed in high RFI locations. This may be good for them but I think it has negative side effects for the kind of precise timing we do, so I'm told. I'm going to ask Dr Clark to handle this one as he understands GPS antennas very well. TAC -- what I'd like to know is if patch is better than helix, if filtered is better than unfiltered, how much amplification is too much, vintage 1990's era antennas vs. 2005 antennas, real splitters vs. Radio Shack splitters, antenna or preamp tempco issues, cable loss and impedance issues, etc. At what ns level does a groundplane start to matter. I guess what we need is some kind of Time Nuts guide to surplus GPS antennas. If it's not possible to give a black and white answer to what kind of antenna is best for a Z3801A-style GPSDO, then at least, what are the factors that make one better than another. And is any of this simple to determine with experimentation? Maybe we can all chip in and test a dozen antenna types to find the answer or to confirm a prediction. /tvb ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts -- w/Java http://www.PRC68.com w/o Java http://www.pacificsites.com/~brooke/PRC68COM.shtml http://www.precisionclock.com ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
