Re: [time-nuts] Important parameters for a GPS/GNSS antenna
In message fc02a5e8-5396-4474-a307-546e10909...@n1k.org, Bob Camp writes: The “put the antenna up and rotate it to see what happens” experiment has indeed been done. The objective was not correcting the antenna’s issues, but validating that their model of the antenna’s phase center was correct. They were trying to see if anechoic chamber data really gave correct answers in free space. So this could be a realistic way for us to calibrate the phase-center of an antenna ? -- 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] Important parameters for a GPS/GNSS antenna
Hi At least according to: ftp://geodesy.noaa.gov/pub/abilich/oldPC/Documents/antcal/calibPapers/Schmitz2002.pdf There are others doing the same thing. Bob On May 9, 2015, at 2:37 AM, Poul-Henning Kamp p...@phk.freebsd.dk wrote: In message fc02a5e8-5396-4474-a307-546e10909...@n1k.org, Bob Camp writes: The “put the antenna up and rotate it to see what happens” experiment has indeed been done. The objective was not correcting the antenna’s issues, but validating that their model of the antenna’s phase center was correct. They were trying to see if anechoic chamber data really gave correct answers in free space. So this could be a realistic way for us to calibrate the phase-center of an antenna ? -- 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] Important parameters for a GPS/GNSS antenna
Probably about the only accurate way, really. A GPS antenna is light weight enough that it could be mounted to a suitable turntable clamped to the shaft of a stepper motor. The assumed physical center of the antenna could be mounted directly on the axis of rotation. Then you would know accurately the angle of rotation. If you plotted the GPS location relative to the angular rotation, you could then know the offset from the assumed physical center, and the real phase center... -Chuck Harris Poul-Henning Kamp wrote: In message fc02a5e8-5396-4474-a307-546e10909...@n1k.org, Bob Camp writes: The “put the antenna up and rotate it to see what happens” experiment has indeed been done. The objective was not correcting the antenna’s issues, but validating that their model of the antenna’s phase center was correct. They were trying to see if anechoic chamber data really gave correct answers in free space. So this could be a realistic way for us to calibrate the phase-center of an antenna ? ___ 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] Important parameters for a GPS/GNSS antenna
On 5/8/15 11:37 PM, Poul-Henning Kamp wrote: In message fc02a5e8-5396-4474-a307-546e10909...@n1k.org, Bob Camp writes: The “put the antenna up and rotate it to see what happens” experiment has indeed been done. The objective was not correcting the antenna’s issues, but validating that their model of the antenna’s phase center was correct. They were trying to see if anechoic chamber data really gave correct answers in free space. So this could be a realistic way for us to calibrate the phase-center of an antenna ? Yes.. actually, the best way in the long run would be to collect many hours of GPS satellite data (carrier phase) with the antenna in one position. Then rotate the antenna to a new position, collect a bunch more data, repeat, etc. Then, you post process using the known position of the satellite, which gives you a direction of arrival relative to the antenna. You probably don't need so have a real precise position for the antenna: the apparent motion of the phase center as a function of az/el is probably fairly slow. Isn't that how they collected phase center data for all those antennas on the UNAVCO site: http://facility.unavco.org/kb/questions/458/UNAVCO+Resources%3A+GNSS+Antennas one of the reports has this interesting statement: Antenna rotation tests work well to identify inconsistencies in mean phase center offsets. By occupying a short baseline (less than 10 meters) and rotating the antenna orientation 180 degrees it is possible to see changes in the baseline length caused by the antenna phase center. For antennas of the same type, the rotation tests will highlight variations of an individual antenna relative to the pool of antennas. ___ 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] Important parameters for a GPS/GNSS antenna
In message 554bc3c3.7090...@earthlink.net, Jim Lux writes: I wonder if anybody ever made a rotating GPS antenna to average out the X-Y phase-center offset ? There is a severe mechanical problem with that. Moving contacts are very hard to keep electrically stable You wouldn't need any of that because there is no need for continous one way rotation, a piece of coax would do just fine. Simply rotate the antenna forth an back between 0 and 360 degree compas. Let the coax drop from the antenna to a horizontal coil so that the stress is converted from torsion to longitudal tension and you'de don. Doing continous rotation may not even be a good idea, rotating 90 degrees every hour is probably a better idea from a processing point of view, as that wouldn't need special software. -- 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] Important parameters for a GPS/GNSS antenna
Hi The “put the antenna up and rotate it to see what happens” experiment has indeed been done. The objective was not correcting the antenna’s issues, but validating that their model of the antenna’s phase center was correct. They were trying to see if anechoic chamber data really gave correct answers in free space. Bob On May 7, 2015, at 5:02 PM, Poul-Henning Kamp p...@phk.freebsd.dk wrote: In message 554bc3c3.7090...@earthlink.net, Jim Lux writes: I wonder if anybody ever made a rotating GPS antenna to average out the X-Y phase-center offset ? There is a severe mechanical problem with that. Moving contacts are very hard to keep electrically stable You wouldn't need any of that because there is no need for continous one way rotation, a piece of coax would do just fine. Simply rotate the antenna forth an back between 0 and 360 degree compas. Let the coax drop from the antenna to a horizontal coil so that the stress is converted from torsion to longitudal tension and you'de don. Doing continous rotation may not even be a good idea, rotating 90 degrees every hour is probably a better idea from a processing point of view, as that wouldn't need special software. -- 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. ___ 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] Important parameters for a GPS/GNSS antenna
Also consider phase wind up. http://www.navipedia.net/index.php/Carrier_Phase_Wind-up_Effect Sure there are also some papers on rotating antennas. http://www.researchgate.net/profile/Simon_Banville/publication/257945217_Antenna_Rotation_and_Its_Effects_on_Kinematic_Precise_Point_Positioning/links/0deec5266c9c6ac71800.pdf Due to the polarization of GPS signals, carrier-phase measurements made by GPS receivers are affected by the orientation of the antenna. On the other hand, code measurements are not affected by this effect. -- Björn I'm curious whether it would need 360 degree rotation? Would simply cycling about 120 degrees on the end of a short arm be just as good and could be done without a rotary joint? I understand that now the RX is moving but within a small radius would it be unbearable? Or would 300 degrees around the axis be sufficient? From Tom Holmes, N8ZM On May 7, 2015, at 11:49 AM, John Ackermann N8UR j...@febo.com wrote: Just put the GPS antenna, receiver, battery, and a low power RF transmitter modulated by the PPS (wide bandwidth = fast edge time) on the turntable, then use an appropriate receiver to demodulate the PPS and feed it to the rest of the system. Put the RX antenna directly above (or below) the turntable so the path length remains close to constant. Using FM might also remove Doppler effects from the received pulse. On 5/7/2015 11:18 AM, Tom Van Baak wrote: I wonder if anybody ever made a rotating GPS antenna to average out the X-Y phase-center offset ? Of course, this does not really work with a gps antenna, unless you put the whole receiver onto the rotary table. But then you shift the problem onto the PPS output (note: amplitude noise translates into phase noise). Attila, My thought was to put PHK's proposed experiment entirely on the rotating table: antenna, receiver, local Cs standard, laptop, and battery. You could also get interesting data if you slightly offset the antenna from the center. It would make the ultimate GPS Spirograph. (for those of you under 40, http://en.wikipedia.org/wiki/Spirograph will explain) /tvb ___ 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. ___ 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] Important parameters for a GPS/GNSS antenna
I'm curious whether it would need 360 degree rotation? Would simply cycling about 120 degrees on the end of a short arm be just as good and could be done without a rotary joint? I understand that now the RX is moving but within a small radius would it be unbearable? Or would 300 degrees around the axis be sufficient? From Tom Holmes, N8ZM On May 7, 2015, at 11:49 AM, John Ackermann N8UR j...@febo.com wrote: Just put the GPS antenna, receiver, battery, and a low power RF transmitter modulated by the PPS (wide bandwidth = fast edge time) on the turntable, then use an appropriate receiver to demodulate the PPS and feed it to the rest of the system. Put the RX antenna directly above (or below) the turntable so the path length remains close to constant. Using FM might also remove Doppler effects from the received pulse. On 5/7/2015 11:18 AM, Tom Van Baak wrote: I wonder if anybody ever made a rotating GPS antenna to average out the X-Y phase-center offset ? Of course, this does not really work with a gps antenna, unless you put the whole receiver onto the rotary table. But then you shift the problem onto the PPS output (note: amplitude noise translates into phase noise). Attila, My thought was to put PHK's proposed experiment entirely on the rotating table: antenna, receiver, local Cs standard, laptop, and battery. You could also get interesting data if you slightly offset the antenna from the center. It would make the ultimate GPS Spirograph. (for those of you under 40, http://en.wikipedia.org/wiki/Spirograph will explain) /tvb ___ 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. ___ 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] Important parameters for a GPS/GNSS antenna
Personally I would be happy with PPS time resolution at 10 nanoseconds but others would want better than a nanosecond. Gotcha with modulating the PPS onto a RF carrier, is that for time resolution of 1 nanosecond, you would end up using a Gigahertz of bandwidth. Tim N3QE On Thu, May 7, 2015 at 11:49 AM, John Ackermann N8UR j...@febo.com wrote: Just put the GPS antenna, receiver, battery, and a low power RF transmitter modulated by the PPS (wide bandwidth = fast edge time) on the turntable, then use an appropriate receiver to demodulate the PPS and feed it to the rest of the system. Put the RX antenna directly above (or below) the turntable so the path length remains close to constant. Using FM might also remove Doppler effects from the received pulse. On 5/7/2015 11:18 AM, Tom Van Baak wrote: I wonder if anybody ever made a rotating GPS antenna to average out the X-Y phase-center offset ? Of course, this does not really work with a gps antenna, unless you put the whole receiver onto the rotary table. But then you shift the problem onto the PPS output (note: amplitude noise translates into phase noise). Attila, My thought was to put PHK's proposed experiment entirely on the rotating table: antenna, receiver, local Cs standard, laptop, and battery. You could also get interesting data if you slightly offset the antenna from the center. It would make the ultimate GPS Spirograph. (for those of you under 40, http://en.wikipedia.org/wiki/Spirograph will explain) /tvb ___ 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. ___ 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] Important parameters for a GPS/GNSS antenna
On Thu, 7 May 2015 08:18:05 -0700 Tom Van Baak t...@leapsecond.com wrote: Attila, My thought was to put PHK's proposed experiment entirely on the rotating table: antenna, receiver, local Cs standard, laptop, and battery. Then you have to be carefull, that the rotation does not modulate the reference. I am pretty sure rotation would at least shift the Cs frequency (atoms fly in an arc) and thus any change in rotation speed would be visible in the measurement. An vapor cell Rb might be better for that case. The periodic shift of the magnetic field would also need to be considered. Maybe the best way would to put the GPS receiver onto the rotating table as well, modulate some laser which points down the middle of the central shaft, and extract that using a small aperture and a photodiode. (The aperture to make sure that only light commming down the exactly in the center is used). This way the reference would be at a stable place, yet the transfer of the signal would be quite stable. You could also get interesting data if you slightly offset the antenna from the center. It would make the ultimate GPS Spirograph. (for those of you under 40, http://en.wikipedia.org/wiki/Spirograph will explain) Hehe. That would be really cool! Attila Kinali -- It is upon moral qualities that a society is ultimately founded. All the prosperity and technological sophistication in the world is of no use without that foundation. -- Miss Matheson, The Diamond Age, Neil Stephenson ___ 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] Important parameters for a GPS/GNSS antenna
On Thu, 7 May 2015 14:43:44 -0400 Tim Shoppa tsho...@gmail.com wrote: Gotcha with modulating the PPS onto a RF carrier, is that for time resolution of 1 nanosecond, you would end up using a Gigahertz of bandwidth. Not really. You are not doing detection in frequency space or of an infintely sharp pulse. As such it is ok if you are bandlimited. Then you just have to ensure that the risinge edge (or whichever you detect) has always the same shape and you detect always at the same level. It is basically the same principle with which we get sup-ns resolution with PPS pulses. The wire isn't good for a bandwidth of 1GHz, usually much less than that (especially the connectors), but as the pulse does not have a very steep edge, it does not need to. Insted the pulse amplitude and the detection level are kept as constant as possible. Of course, any variation in amplitude, detection level or noise degrades the measurement considerably. Attila Kinali -- _av500_ phd is easy _av500_ getting dsl is hard ___ 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] Important parameters for a GPS/GNSS antenna
tsho...@gmail.com said: Gotcha with modulating the PPS onto a RF carrier, is that for time resolution of 1 nanosecond, you would end up using a Gigahertz of bandwidth. You might be able to use near-field antennas. Picture 2 PCBs spaced a few mm apart with circular antennas. It would be interesting to measure all the timing quirks of not having things lined up accurately. -- These are my opinions. 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] Important parameters for a GPS/GNSS antenna
How about a laser diode and pin photo detector? You should be able to get nanosecond resolution with light. - Original Message - From: Tim Shoppa tsho...@gmail.com To: Discussion of precise time and frequency measurement time-nuts@febo.com Sent: Thursday, May 07, 2015 2:43 PM Subject: Re: [time-nuts] Important parameters for a GPS/GNSS antenna Personally I would be happy with PPS time resolution at 10 nanoseconds but others would want better than a nanosecond. Gotcha with modulating the PPS onto a RF carrier, is that for time resolution of 1 nanosecond, you would end up using a Gigahertz of bandwidth. Tim N3QE On Thu, May 7, 2015 at 11:49 AM, John Ackermann N8UR j...@febo.com wrote: Just put the GPS antenna, receiver, battery, and a low power RF transmitter modulated by the PPS (wide bandwidth = fast edge time) on the turntable, then use an appropriate receiver to demodulate the PPS and feed it to the rest of the system. Put the RX antenna directly above (or below) the turntable so the path length remains close to constant. Using FM might also remove Doppler effects from the received pulse. On 5/7/2015 11:18 AM, Tom Van Baak wrote: I wonder if anybody ever made a rotating GPS antenna to average out the X-Y phase-center offset ? Of course, this does not really work with a gps antenna, unless you put the whole receiver onto the rotary table. But then you shift the problem onto the PPS output (note: amplitude noise translates into phase noise). Attila, My thought was to put PHK's proposed experiment entirely on the rotating table: antenna, receiver, local Cs standard, laptop, and battery. You could also get interesting data if you slightly offset the antenna from the center. It would make the ultimate GPS Spirograph. (for those of you under 40, http://en.wikipedia.org/wiki/Spirograph will explain) /tvb ___ 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. ___ 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] Important parameters for a GPS/GNSS antenna
On 5/7/15 7:23 AM, Attila Kinali wrote: On Sun, 03 May 2015 07:29:30 + Poul-Henning Kamp p...@phk.freebsd.dk wrote: When you post-process raw GPS data you get to include antenna phase center / gain / az/el corrections for free. Speaking of which... I wonder if anybody ever made a rotating GPS antenna to average out the X-Y phase-center offset ? There is a severe mechanical problem with that. Moving contacts are very hard to keep electrically stable. It works for simple power and digital signal wires, as there the only considerations are resistance over the joint and sparks. If you need to transmit analog signals you generally convert them into a form that does not depend on the amplitude of the signal (either going digital or doing a voltage to frequency conversion). Of course, this does not really work with a gps antenna, unless you put the whole receiver onto the rotary table. But then you shift the problem onto the PPS output (note: amplitude noise translates into phase noise). The best system i know about, for such rotating contacts with analog (possibly high frequency) signals is a small pot with mercury. But i guess you can see the problems that causes. The second best, but which only works with high frequency signals, is to use a hollow waveguide. There you need only to ensure that the waveguide walls are properly connected and you have a large area to use for that. If you can ensure that there is only one mode, you can make it such, that there is no current flowing over the gap. They make rotary coax joints as well as waveguide. The coax is an air dielectric type. There is, inevitably, some wow and flutter in S21 (and S11) ___ 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] Important parameters for a GPS/GNSS antenna
On Sat, 2 May 2015 13:25:16 -0400 Bob Camp kb...@n1k.org wrote: Phase / delay stability over temperature would be an interesting thing to look at. Probably not a big deal on a simple antenna. It might be an issue as the antenna interacts with the preamp and filter. I've seen a couple of papers concerning this. I haven't sorted them in yet (much less read), so i cannot give you the names and doi yet. But if you are interested i can do so over the weekend. Attila Kinali -- It is upon moral qualities that a society is ultimately founded. All the prosperity and technological sophistication in the world is of no use without that foundation. -- Miss Matheson, The Diamond Age, Neil Stephenson ___ 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] Important parameters for a GPS/GNSS antenna
On Sun, 03 May 2015 07:29:30 + Poul-Henning Kamp p...@phk.freebsd.dk wrote: When you post-process raw GPS data you get to include antenna phase center / gain / az/el corrections for free. Speaking of which... I wonder if anybody ever made a rotating GPS antenna to average out the X-Y phase-center offset ? There is a severe mechanical problem with that. Moving contacts are very hard to keep electrically stable. It works for simple power and digital signal wires, as there the only considerations are resistance over the joint and sparks. If you need to transmit analog signals you generally convert them into a form that does not depend on the amplitude of the signal (either going digital or doing a voltage to frequency conversion). Of course, this does not really work with a gps antenna, unless you put the whole receiver onto the rotary table. But then you shift the problem onto the PPS output (note: amplitude noise translates into phase noise). The best system i know about, for such rotating contacts with analog (possibly high frequency) signals is a small pot with mercury. But i guess you can see the problems that causes. The second best, but which only works with high frequency signals, is to use a hollow waveguide. There you need only to ensure that the waveguide walls are properly connected and you have a large area to use for that. If you can ensure that there is only one mode, you can make it such, that there is no current flowing over the gap. Attila Kinali -- It is upon moral qualities that a society is ultimately founded. All the prosperity and technological sophistication in the world is of no use without that foundation. -- Miss Matheson, The Diamond Age, Neil Stephenson ___ 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] Important parameters for a GPS/GNSS antenna
On Sat, 02 May 2015 18:36:30 +0200 Magnus Danielson mag...@rubidium.dyndns.org wrote: On 04/29/2015 10:43 PM, Attila Kinali wrote: Moin, I recently discovered openEMS[1], which is, very simply put, a fancy antenna simulator. I played a little with it and thought about trying to optimize an GPS patch antenna design for timing use. Will take it for a test-drive to see how it align up to NEC2 and variants. I'm pretty sure that OpenEMS will be more accurate in most cases. OpenEMS uses a more general approach to solving Maxwells equations that works for patterned conductors as well. While NEC2 is known to work well only for wires and cylinders (even tappered antennas cause large inaccuracies). My google skills failed to locate any relevant documents on this topic. Could someone be so kind and give me some pointers, what to search for, documents or the like? The thing that we care about is: 1) LHCP surpression 2) Directivity/ surpression of signals below say 5 degrees above horizon 3) Phase stability with regard to azimuth/elevation 4) Relatively flat gain above 5 degrees Yes. In the meantime I found [1]. I only skimmed over an electronic version so far, but the gist of it seems that multipath supression comes first, before anything else. Ie RHCP/LHCP ratio and supression of everything below 5°-10°. After that, it's phase center stability. Other factors do not seem to matter as much (not sure, it could be that I just didnt read enough of the book) Do read up on the Novatel pinwheels, as they illustrate the various concerns and how they do that in a new fashion. I read most of the papers and the patents I found. While enlightening on some aspects, they do not tell much about the tradeoffs. Also I had some facepalm-moments on what is patentable But then, the first pinwheel patent is to expire in 4 years, so that problem solves itself. Attila Kinali [1] GPS/GNSS Antennas, by Rama Rao, Kunysz, Fante, McDonald, 2012, ISBN: 978-1596931503 -- It is upon moral qualities that a society is ultimately founded. All the prosperity and technological sophistication in the world is of no use without that foundation. -- Miss Matheson, The Diamond Age, Neil Stephenson ___ 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] Important parameters for a GPS/GNSS antenna
I wonder if anybody ever made a rotating GPS antenna to average out the X-Y phase-center offset ? Of course, this does not really work with a gps antenna, unless you put the whole receiver onto the rotary table. But then you shift the problem onto the PPS output (note: amplitude noise translates into phase noise). Attila, My thought was to put PHK's proposed experiment entirely on the rotating table: antenna, receiver, local Cs standard, laptop, and battery. You could also get interesting data if you slightly offset the antenna from the center. It would make the ultimate GPS Spirograph. (for those of you under 40, http://en.wikipedia.org/wiki/Spirograph will explain) /tvb ___ 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] Important parameters for a GPS/GNSS antenna
Just put the GPS antenna, receiver, battery, and a low power RF transmitter modulated by the PPS (wide bandwidth = fast edge time) on the turntable, then use an appropriate receiver to demodulate the PPS and feed it to the rest of the system. Put the RX antenna directly above (or below) the turntable so the path length remains close to constant. Using FM might also remove Doppler effects from the received pulse. On 5/7/2015 11:18 AM, Tom Van Baak wrote: I wonder if anybody ever made a rotating GPS antenna to average out the X-Y phase-center offset ? Of course, this does not really work with a gps antenna, unless you put the whole receiver onto the rotary table. But then you shift the problem onto the PPS output (note: amplitude noise translates into phase noise). Attila, My thought was to put PHK's proposed experiment entirely on the rotating table: antenna, receiver, local Cs standard, laptop, and battery. You could also get interesting data if you slightly offset the antenna from the center. It would make the ultimate GPS Spirograph. (for those of you under 40, http://en.wikipedia.org/wiki/Spirograph will explain) /tvb ___ 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] Important parameters for a GPS/GNSS antenna
In message B373DA32B0D748A9B45D90A7D38B2C32@pc52, Tom Van Baak writes: When you post-process raw GPS data you get to include antenna phase center / gain / az/el corrections for free. Speaking of which... I wonder if anybody ever made a rotating GPS antenna to average out the X-Y phase-center offset ? -- 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] Important parameters for a GPS/GNSS antenna
I wonder if anybody ever made a rotating GPS antenna to average out the X-Y phase-center offset ? PHK, I ran across this wonderful shaker table experiment and concluded that post-processing would always be better than playing moving antenna games. See pages 9-13 of: http://www.nceo.ac.uk/assets/presentations/2012_conference_NOTTINGHAM/NCEOCONF2012_0919_Atkins.pdf If nothing else, it makes a wonderful test of your GPS receiver's time/position resolution. Something to do with an old 33 RPM turntable... /tvb ___ 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] Important parameters for a GPS/GNSS antenna
Hi Obviously this becomes a “that depends” sort of question. For timing, you probably can do a fine job with an antenna that nukes everything below 20 degrees to the horizon. That *assumes* that you have a good enough view that it does not pull to many sat’s out of your population *and* that you already know your location. Phase / delay stability over temperature would be an interesting thing to look at. Probably not a big deal on a simple antenna. It might be an issue as the antenna interacts with the preamp and filter. Bob On May 2, 2015, at 12:36 PM, Magnus Danielson mag...@rubidium.dyndns.org wrote: Attila, On 04/29/2015 10:43 PM, Attila Kinali wrote: Moin, I recently discovered openEMS[1], which is, very simply put, a fancy antenna simulator. I played a little with it and thought about trying to optimize an GPS patch antenna design for timing use. Will take it for a test-drive to see how it align up to NEC2 and variants. But I had to discover that I actually do not know what to optimze for. There are many paramters I can think of (RHCP/LHCP, symmetry of gain, feedpoint impedance vs frequency, stability of phase centre,) which all seem to be to some extend important, but which ones do actually matter for the timing reference performance? My google skills failed to locate any relevant documents on this topic. Could someone be so kind and give me some pointers, what to search for, documents or the like? The thing that we care about is: 1) LHCP surpression 2) Directivity/ surpression of signals below say 5 degrees above horizon 3) Phase stability with regard to azimuth/elevation 4) Relatively flat gain above 5 degrees Do read up on the Novatel pinwheels, as they illustrate the various concerns and how they do that in a new fashion. 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. ___ 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] Important parameters for a GPS/GNSS antenna
A tri-band antenna design is... uh.. difficult. At the moment I am just playing with some software. Yes, I might end up with something that resembles an antenna design. But with my level of knowledge getting a good single band antenna would be already quite some feat. Designing a multi-band antenna is way out of my league. Attila Kinali Hi Attila, One other consideration is that for high-end positioning and timing use, an accurate characterization of a given antenna is more important than trying to achieve a perfect antenna. When you post-process raw GPS data you get to include antenna phase center / gain / az/el corrections for free. This means the goal is not so much a perfect antenna design, but an antenna whose imperfections are well-known. Here are a dozen random GPS antenna calibration links to keep you busy for today: National Geodetic Survey Absolute Antenna Calibrations http://www.gps.gov/cgsic/meetings/2010/bilich.pdf Leica GNSS Reference Antennas - White Paper http://www.leica-geosystems.com/downloads123/zz/nrs/general/white-tech-paper/Leica_Reference_Antennas_Whitepaper_TPA_en.pdf A Novel GPS Survey Antenna http://www.meridware.com.tw/Documents/Papers/gps600antenna.pdf Tests of phase center variations of various GPS antennas, and some results ftp://geodesy.noaa.gov/pub/abilich/oldPC/Documents/antcal/calibPapers/Schmitz2002.pdf GPS ANTENNA CALIBRATION AT THE NATIONAL GEODETIC SURVEY https://www.fig.net/pub/fig2008/ppt/ts05g/ts05g_02_weston_mader_ppt_2857.pdf A New Approach for Field Calibration of Absolute Antenna Phase Center Variations http://www.geopp.com/pdf/ion96.pdf ANTENNA PHASE CENTER VARIATIONS CORRECTIONS IN PROCESSING OF GPS OBSERVATIONS WITH USE OF COMMERCIAL SOFTWARE http://www.uwm.edu.pl/wnt/technicalsc/tech_13/B12.PDF Phase center variations problem in GPS/GLONASS observations processing http://leidykla.vgtu.lt/conferences/ENVIRO_2014/Articles/5/202_Dawidowicz.pdf Calibration of antenna-radome and monument-multipath effect of GEONET—Part 1: Measurement of phase characteristics http://svr4.terrapub.co.jp/journals/EPS/pdf/2001/5301/53010013.pdf Absolute phase center corrections of satellite and receiver antennas http://www.dgfi.tum.de/media/jahresbericht/publications/4558dbb6f6f8bb2e16d03b85bde76e2c.pdf Phase Center Calibration and Multipath Test Results of a Digital Beam-Steered Antenna Array http://navsys.com/Papers/0309002.pdf /tvb ___ 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] Important parameters for a GPS/GNSS antenna
Attila, On 04/29/2015 10:43 PM, Attila Kinali wrote: Moin, I recently discovered openEMS[1], which is, very simply put, a fancy antenna simulator. I played a little with it and thought about trying to optimize an GPS patch antenna design for timing use. Will take it for a test-drive to see how it align up to NEC2 and variants. But I had to discover that I actually do not know what to optimze for. There are many paramters I can think of (RHCP/LHCP, symmetry of gain, feedpoint impedance vs frequency, stability of phase centre,) which all seem to be to some extend important, but which ones do actually matter for the timing reference performance? My google skills failed to locate any relevant documents on this topic. Could someone be so kind and give me some pointers, what to search for, documents or the like? The thing that we care about is: 1) LHCP surpression 2) Directivity/ surpression of signals below say 5 degrees above horizon 3) Phase stability with regard to azimuth/elevation 4) Relatively flat gain above 5 degrees Do read up on the Novatel pinwheels, as they illustrate the various concerns and how they do that in a new fashion. 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] Important parameters for a GPS/GNSS antenna
On Thu, 30 Apr 2015 17:19:22 + Gregory Maxwell gmaxw...@gmail.com wrote: I have no experience in the subject, but one parameter I didn't see you mention is front/back ratio-- it should have the lowest gain possible for angles below whatever you would horizon mask in order to suppress multipath coming in from lower elevations. Yes, radiation pattern is probably the first thing to optimize. But low angle/back lobe damping is rather easy to acheive by some EBG around the antenna (like choke rings). Integrating into a compact antenna is much more difficult. Operation at all the relevant GNSS bands would be good to optimize for too, and might be a major motivation for a new public design as multibanded antennas for timing applications are quite costly and tough to find surplus. A tri-band antenna design is... uh.. difficult. At the moment I am just playing with some software. Yes, I might end up with something that resembles an antenna design. But with my level of knowledge getting a good single band antenna would be already quite some feat. Designing a multi-band antenna is way out of my league. Attila Kinali -- It is upon moral qualities that a society is ultimately founded. All the prosperity and technological sophistication in the world is of no use without that foundation. -- Miss Matheson, The Diamond Age, Neil Stephenson ___ 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] Important parameters for a GPS/GNSS antenna
Moin, I recently discovered openEMS[1], which is, very simply put, a fancy antenna simulator. I played a little with it and thought about trying to optimize an GPS patch antenna design for timing use. But I had to discover that I actually do not know what to optimze for. There are many paramters I can think of (RHCP/LHCP, symmetry of gain, feedpoint impedance vs frequency, stability of phase centre,) which all seem to be to some extend important, but which ones do actually matter for the timing reference performance? My google skills failed to locate any relevant documents on this topic. Could someone be so kind and give me some pointers, what to search for, documents or the like? Attila Kinali [1] http://openems.de -- _av500_ phd is easy _av500_ getting dsl is hard ___ 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.
