Re: [time-nuts] OT - GPS and North
alternately you could use a short-haul modem. I've used the ones from Telebyte running over with good success. you can get up to 115.2 kbps on ~1km of cable on some of them. http://www.telebyteusa.com/shorthaulmodem.htm -eric On Mon, Nov 23, 2009 at 7:37 AM, Justin Pinnix wrote: > Hi Rex, > > Sounds like a neat application. 100 meters might be a bit long for RS-232. > I was taught that 50 feet is the limit for 9600bps. You may need to use > RS-422 (balanced version of 232), low capacitance cable, or a lower baud > rate. Since you're a ham, you could also do it wirelessly over UHF packet. > You might even be able to use existing APRS hardware, provided it leaves you > enough significant digits. > > 73 de AJ4MJ > > On Sun, Nov 22, 2009 at 8:39 PM, Rex Moncur wrote: > >> Given that we cannot do it with one GPS in a fixed position I would like to >> get people's ideas on whether there is a reasonable cost way (say less than >> $2K) to do it with two GPSs to get within a say half a degree. >> >> >> The application is to find azimuth headings for Amateur radio microwave or >> lightwave experiments. One cannot normally do star shots due to either day >> light or clouds. >> >> Let us assume that you can run the two GPS's over a baseline of 100 meters. >> At present I can get to within about plus/minus two degrees by walking an >> inexpensive handheld GPS over a baseline of 100 meters but I want to do >> better than that. For the hopefully more accurate measurement I would place >> one GPS and antenna at the microwave dish or lightwave transmitter and the >> other would be set up 100 meters away roughly in the direction one needed >> to >> beam. When a bearing was found one could either readjust the position of >> the >> remote GPS antenna to improve the accuracy or just allow for any error by >> beaming by this amount to the GPS unit. >> >> Let us assume that both GPS antennas are in a fixed location and the >> results can be averaged over say 30 minutes to improve the accuracy. I >> assume also that many of the errors due to propagation would cancel over >> such a short path. The data from both GPSs would be fed to a laptop over >> say RS232 line which I hope would work for 100 meters (perhaps 50 meters >> each way if necessary). The Laptop would have software to process that >> data >> and provide a bearing between the two antennas. Can anyone comment on: >> >> (a) the likely accuracy of such a system >> (b) whether there is any software out there that can do this. >> (c) the recommended GPS units for this application. >> (d) whether there is something one could purchase as a complete package at >> a >> reasonable cost (ie less than $2k) >> >> 73 Rex VK7MO >> >> >> >> >> >> -Original Message- >> From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On >> Behalf Of iov...@inwind.it >> Sent: Monday, 23 November 2009 8:08 AM >> To: time-nuts >> Subject: Re: [time-nuts] OT - GPS and North >> >> Thanks all. >> >> The conclusion seems to be that an ordinary and stationary GPS receiver >> with >> a single >> omnidiretional antenna knows very well where satellites are relative to the >> true North, >> and where the true North is relative to satellites, but doesn't know (more >> precisely: >> can't indicate, as it lacks another reference) where satellites or the >> North >> actually are. >> Eventually this appears quite obvious. >> >> Antonio I8IOV >> >> >> ___ >> 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. > -- --Eric _ Eric Garner ___ 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] OT - GPS and North
Hi Rex, Sounds like a neat application. 100 meters might be a bit long for RS-232. I was taught that 50 feet is the limit for 9600bps. You may need to use RS-422 (balanced version of 232), low capacitance cable, or a lower baud rate. Since you're a ham, you could also do it wirelessly over UHF packet. You might even be able to use existing APRS hardware, provided it leaves you enough significant digits. 73 de AJ4MJ On Sun, Nov 22, 2009 at 8:39 PM, Rex Moncur wrote: > Given that we cannot do it with one GPS in a fixed position I would like to > get people's ideas on whether there is a reasonable cost way (say less than > $2K) to do it with two GPSs to get within a say half a degree. > > > The application is to find azimuth headings for Amateur radio microwave or > lightwave experiments. One cannot normally do star shots due to either day > light or clouds. > > Let us assume that you can run the two GPS's over a baseline of 100 meters. > At present I can get to within about plus/minus two degrees by walking an > inexpensive handheld GPS over a baseline of 100 meters but I want to do > better than that. For the hopefully more accurate measurement I would place > one GPS and antenna at the microwave dish or lightwave transmitter and the > other would be set up 100 meters away roughly in the direction one needed > to > beam. When a bearing was found one could either readjust the position of > the > remote GPS antenna to improve the accuracy or just allow for any error by > beaming by this amount to the GPS unit. > > Let us assume that both GPS antennas are in a fixed location and the > results can be averaged over say 30 minutes to improve the accuracy. I > assume also that many of the errors due to propagation would cancel over > such a short path. The data from both GPSs would be fed to a laptop over > say RS232 line which I hope would work for 100 meters (perhaps 50 meters > each way if necessary). The Laptop would have software to process that > data > and provide a bearing between the two antennas. Can anyone comment on: > > (a) the likely accuracy of such a system > (b) whether there is any software out there that can do this. > (c) the recommended GPS units for this application. > (d) whether there is something one could purchase as a complete package at > a > reasonable cost (ie less than $2k) > > 73 Rex VK7MO > > > > > > -Original Message- > From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On > Behalf Of iov...@inwind.it > Sent: Monday, 23 November 2009 8:08 AM > To: time-nuts > Subject: Re: [time-nuts] OT - GPS and North > > Thanks all. > > The conclusion seems to be that an ordinary and stationary GPS receiver > with > a single > omnidiretional antenna knows very well where satellites are relative to the > true North, > and where the true North is relative to satellites, but doesn't know (more > precisely: > can't indicate, as it lacks another reference) where satellites or the > North > actually are. > Eventually this appears quite obvious. > > Antonio I8IOV > > > ___ > 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] OT - GPS and North
> >> You could (temporarily) install a structure that blocks reception in one > >> direction and then infer the meridian direction from the occultation of > >> SVs by the obstruction. > >> However the accuracy of the determination wont be high. > >> > >> Bruce > > > > Anyway, that's an idea. > > > > Antonio > > The other way to find North is to monitor the shadow cast > by the "temporary structure". For details, google sundial. > > /tvb Would be more accurate, for sure, but not good at night :-). Antonio ___ 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] OT - GPS and North
Hi Rex: You can do it with a single GPS (DAGR or PLGR96 or higher) with a 100 meter baseline. See: http://www.prc68.com/I/DAGR.shtml#GLS http://www.prc68.com/I/DAGR.shtml#AzD Have Fun, Brooke Clarke http://www.prc68.com Rex Moncur wrote: Given that we cannot do it with one GPS in a fixed position I would like to get people's ideas on whether there is a reasonable cost way (say less than $2K) to do it with two GPSs to get within a say half a degree. The application is to find azimuth headings for Amateur radio microwave or lightwave experiments. One cannot normally do star shots due to either day light or clouds. Let us assume that you can run the two GPS's over a baseline of 100 meters. At present I can get to within about plus/minus two degrees by walking an inexpensive handheld GPS over a baseline of 100 meters but I want to do better than that. For the hopefully more accurate measurement I would place one GPS and antenna at the microwave dish or lightwave transmitter and the other would be set up 100 meters away roughly in the direction one needed to beam. When a bearing was found one could either readjust the position of the remote GPS antenna to improve the accuracy or just allow for any error by beaming by this amount to the GPS unit. Let us assume that both GPS antennas are in a fixed location and the results can be averaged over say 30 minutes to improve the accuracy. I assume also that many of the errors due to propagation would cancel over such a short path. The data from both GPSs would be fed to a laptop over say RS232 line which I hope would work for 100 meters (perhaps 50 meters each way if necessary). The Laptop would have software to process that data and provide a bearing between the two antennas. Can anyone comment on: (a) the likely accuracy of such a system (b) whether there is any software out there that can do this. (c) the recommended GPS units for this application. (d) whether there is something one could purchase as a complete package at a reasonable cost (ie less than $2k) 73 Rex VK7MO -Original Message- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of iov...@inwind.it Sent: Monday, 23 November 2009 8:08 AM To: time-nuts Subject: Re: [time-nuts] OT - GPS and North Thanks all. The conclusion seems to be that an ordinary and stationary GPS receiver with a single omnidiretional antenna knows very well where satellites are relative to the true North, and where the true North is relative to satellites, but doesn't know (more precisely: can't indicate, as it lacks another reference) where satellites or the North actually are. Eventually this appears quite obvious. Antonio I8IOV ___ 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] OT - GPS and North
Given that we cannot do it with one GPS in a fixed position I would like to get people's ideas on whether there is a reasonable cost way (say less than $2K) to do it with two GPSs to get within a say half a degree. The application is to find azimuth headings for Amateur radio microwave or lightwave experiments. One cannot normally do star shots due to either day light or clouds. Let us assume that you can run the two GPS's over a baseline of 100 meters. At present I can get to within about plus/minus two degrees by walking an inexpensive handheld GPS over a baseline of 100 meters but I want to do better than that. For the hopefully more accurate measurement I would place one GPS and antenna at the microwave dish or lightwave transmitter and the other would be set up 100 meters away roughly in the direction one needed to beam. When a bearing was found one could either readjust the position of the remote GPS antenna to improve the accuracy or just allow for any error by beaming by this amount to the GPS unit. Let us assume that both GPS antennas are in a fixed location and the results can be averaged over say 30 minutes to improve the accuracy. I assume also that many of the errors due to propagation would cancel over such a short path. The data from both GPSs would be fed to a laptop over say RS232 line which I hope would work for 100 meters (perhaps 50 meters each way if necessary). The Laptop would have software to process that data and provide a bearing between the two antennas. Can anyone comment on: (a) the likely accuracy of such a system (b) whether there is any software out there that can do this. (c) the recommended GPS units for this application. (d) whether there is something one could purchase as a complete package at a reasonable cost (ie less than $2k) 73 Rex VK7MO -Original Message- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of iov...@inwind.it Sent: Monday, 23 November 2009 8:08 AM To: time-nuts Subject: Re: [time-nuts] OT - GPS and North Thanks all. The conclusion seems to be that an ordinary and stationary GPS receiver with a single omnidiretional antenna knows very well where satellites are relative to the true North, and where the true North is relative to satellites, but doesn't know (more precisely: can't indicate, as it lacks another reference) where satellites or the North actually are. Eventually this appears quite obvious. Antonio I8IOV ___ 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] OT - GPS and North
Brooke No idea about MD1 connections source. I can well believe that the photocell plus telescope is capable of arc second accuracy sensitivity. Zeiss used to offer a sun tracker as well as photomultiplier based tridant star sensor/trackers with sub arc second sensitiviy. Bruce Brooke Clarke wrote: Hi Bruce: Do you know where I might find connection information on the MD-1 star tracker used in the B-52? See: http://www.prc68.com/I/MD1.shtml The system was good to 1 arc minute (including temperature, pressure, etc.) and I've heard that the sensor was far better than that (into the arc second range). Have Fun, Brooke Clarke http://www.prc68.com Bruce Griffiths wrote: ___ 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] OT - GPS and North
You could (temporarily) install a structure that blocks reception in one direction and then infer the meridian direction from the occultation of SVs by the obstruction. However the accuracy of the determination wont be high. Bruce Anyway, that's an idea. Antonio The other way to find North is to monitor the shadow cast by the "temporary structure". For details, google sundial. /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] OT - GPS and North
Hi Bruce: Do you know where I might find connection information on the MD-1 star tracker used in the B-52? See: http://www.prc68.com/I/MD1.shtml The system was good to 1 arc minute (including temperature, pressure, etc.) and I've heard that the sensor was far better than that (into the arc second range). Have Fun, Brooke Clarke http://www.prc68.com Bruce Griffiths wrote: When a star tracker is used as a stellar compass in effect takes simultaneous fixes on several stars and the better ones are capable of an rms error of a few arc seconds, largely limited by atmospheric instability. These are usually used for determining space vehicle attitude, in which case the instability due to seeing is much smaller than when immersed in the atmosphere. They have been used as relatively inexpensive position encoders for pointing a telescope to within a few arc seconds. Pattern recognition techniques are used to identify stars in a relatively wide field (a few degrees) slightly defocused image (improves centroiding accuracy). Star tracker for Clementine mission: http://www.osti.gov/bridge/servlets/purl/86977-ULkJcR/webviewable/86977.pdf A more accurate version: http://www.newworldt.com/download/DTU/microASC%20Summary.pdf telescope pointing application: http://www.ifa.hawaii.edu/faculty/pickles/AJP/spie3351.07.pdf http://www.ifa.hawaii.edu/users/pickles/AJP/AMOS2003_v4.pdf Measuring the position (altitude + azimuth) of one star at a time using a theodolite is not the most efficient method of determining the direction of the meridian. Its far better to measure the position of several stars at once as in the stellar compass, however a longer focal length camera lens than usually used in a star tracker is desrable for increased accuracy. Bruce J. Forster wrote: Not so. I'm very familiar with laying in accurate North lines for gyro testing. To get anything close to accurate (1 arc second or better) takes many hours of stellar observation with a Wild T-3 class instrument. -John === Neville Michie wrote: When you think of time specifications from GPS, the GPS system is a poor way to find north. Even with a base line of 1000 metres you only have a fraction of a degree. The GPS system may be useful to get accurate time to simplify a star observation, from a known (GPS) position on this planet, but finding north is still a problem because of the accuracy of a small number of observations from a star fix. Gyrocompasses take some time to get a measurement ( one hour) but even their estimate of North cannot match the precision that the GPS system can get us with time. cheers, Neville Michie If you are taking star shots a stellar compass can easily provide a boresight pointing accuracy of a few arcsec. Bruce ___ 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] OT - GPS and North
Hi Antonio: That's an interesting question. It turns out that one of the key military applications of GPS, in addition to position and time, is to find North to high accuracy. This is needed to be known to better that one grad (1/6400 of a circle). In that past it was done using a theodolite integrated with a gyroscope (AG8 (Kern DKM1) North Finding System). This system was heavy, cost the government about $250k and was very easy to break. http://www.prc68.com/I/Alidade.shtml#AG8 I think starting with the PLGR96 and now the DAGR there are two or more methods of accurately finding North. http://www.prc68.com/I/PLGR.shtml http://www.prc68.com/I/DAGR.shtml#GLS http://www.prc68.com/I/DAGR.shtml#AzD In one method you place the receiver on stake #1, go to stake #2 (while not obstructing the antenna to allow carrier phase tracking sats) then at stake #2 press enter and the GPS gives you the bearing and distance between the stakes. In another method two GPS receivers are used. One at stake #1 and the other first is synchronized to the one at stake #1 then moved to stake #2, press enter, and go back to stake #1 and reconnect the two units. Again you get bearing and distance between the stakes based on carrier phase processing inside the GPS unit. - Many GPS receivers have a built in World Magnetic Model. It's just a 12th order polynomial fitted to the magnetic vector by Lon, Lat, Ele, date & time. They're good for 5 years, see: http://www.prc68.com/I/Sensors.shtml#EMF For example the military DAGR has a built in magnetic compass that has the deviation corrected based on the location and date so you can select either true or magnetic bearings. Using the magnetic compass drains the battery so there's an option to turn it off when not in use. There's no tilt correction so the GPS receiver needs to be held level when using the mag compass. Have Fun, Brooke Clarke http://www.prc68.com iov...@inwind.it wrote: > Does a stationary (not in motion) GPS receiver know where the North is? > > As far > as I can understand, it doesn't, isn't it? > > Antonio I8IOV > > ___ > 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] OT - GPS and North
Hi Antonio: That's an interesting question. It turns out that one of the key military applications of GPS, in addition to position and time, is to find North to high accuracy. This is needed to be known to better that one grad (1/6400 of a circle). In that past it was done using a theodolite integrated with a gyroscope (AG8 (Kern DKM1) North Finding System). This system was heavy, cost the government about $250k and was very easy to break. http://www.prc68.com/I/Alidade.shtml#AG8 I think starting with the PLGR96 and now the DAGR there are two or more methods of accurately finding North. http://www.prc68.com/I/PLGR.shtml http://www.prc68.com/I/DAGR.shtml#GLS http://www.prc68.com/I/DAGR.shtml#AzD In one method you place the receiver on stake #1, go to stake #2 (while not obstructing the antenna to allow carrier phase tracking sats) then at stake #2 press enter and the GPS gives you the bearing and distance between the stakes. In another method two GPS receivers are used. One at stake #1 and the other first is synchronized to the one at stake #1 then moved to stake #2, press enter, and go back to stake #1 and reconnect the two units. Again you get bearing and distance between the stakes based on carrier phase processing inside the GPS unit. Have Fun, Brooke Clarke http://www.prc68.com iov...@inwind.it wrote: Does a stationary (not in motion) GPS receiver know where the North is? As far as I can understand, it doesn't, isn't it? Antonio I8IOV ___ 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] OT - GPS and North
It's going to be hard to use LORAN C, if the system is shut down. -John = > Stanley Reynolds wrote: >> Yes, found this patent : >> >> http://www.freepatentsonline.com/y2008/0186232.html >> >> "A method and radio navigation system compass apparatus for determining >> true north or azimuth or orientation of a vehicle or the like by the use >> of integrated Loran and satellite radio navigation receivers employing >> crossed-loop H-field antennas for the Loran reception, or the use of at >> least three Loran type transmitter, or two Loran type transmitter and a >> synchronized clock for determining both position and azimuth. " >> >> >> synergy, the whole is greater than the sum of the individual parts > > Traditional Directional Finding techniquest combined with positional > information from the Loran-C is a good mix. Question is if the invention > is that big that a good patent would hold. [snip] ___ 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] OT - GPS and North
Stanley Reynolds wrote: Yes, found this patent : http://www.freepatentsonline.com/y2008/0186232.html "A method and radio navigation system compass apparatus for determining true north or azimuth or orientation of a vehicle or the like by the use of integrated Loran and satellite radio navigation receivers employing crossed-loop H-field antennas for the Loran reception, or the use of at least three Loran type transmitter, or two Loran type transmitter and a synchronized clock for determining both position and azimuth. " synergy, the whole is greater than the sum of the individual parts Traditional Directional Finding techniquest combined with positional information from the Loran-C is a good mix. Question is if the invention is that big that a good patent would hold. Both GPS and loran depend on the phase/frequency/time accuracy of their source, but I wonder if other signals not as accurate but maybe short-term stable could be used to improve combined stability such as TV and radio transmitters. With such a large source of possible transmitters comparison of them to GPS and loran to pick a few good ones to add both hold-over from gps and or loran loss. For example a CDMA cell site that is dependent on GPS would slowly deteriorate if GPS was lost, but a large number of CDMA cell sites would continue to work if they could be synced to another source. You can use either the timing or direction or both from many different sources in combination with that of a number of different satellite systems in a combined pseudo-range and orientation input for a position and heading analysis. You can weigth in timing from several VLF sources in combination with the pseudo-ranges of the sats. The problem with VLF sources is the shift in delay due to shift in atmosphere, so their contribution would be limited unless fairly nearby. Besides the hold over capability I would be interested in ways to combine as many independent sources to improve accuracy like the use of more accurate frequency sources to improve GPS accuracy: http://plan.geomatics.ucalgary.ca/papers/ENC06_Paper74_WatsonetAl_v3Web.pdf Or maybe a time-nut antidote would be better ;-) Maybe. :) 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] OT - GPS and North
stanley_reyno...@yahoo.com said: > For example a CDMA cell site that is dependent on GPS would slowly > deteriorate if GPS was lost, but a large number of CDMA cell sites > would continue to work if they could be synced to another source. Unless, of course, that other source was depending on GPS and has the same problem you are having. -- These are my opinions, not necessarily my employer's. I hate spam. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] OT - GPS and North
> iov...@inwind.it wrote: > > Thanks all. > > > > The conclusion seems to be that an ordinary and stationary GPS receiver > > with a single > > omnidiretional antenna knows very well where satellites are relative to the > > true North, > > and where the true North is relative to satellites, but doesn't know (more > > precisely: > > can't indicate, as it lacks another reference) where satellites or the > > North actually are. > > Eventually this appears quite obvious. > > > > Antonio I8IOV > > > > > > > You could (temporarily) install a structure that blocks reception in one > direction and then infer the meridian direction from the occultation of > SVs by the obstruction. > However the accuracy of the determination wont be high. > > Bruce Anyway, that's an idea. Antonio ___ 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] OT - GPS and North
iov...@inwind.it wrote: Thanks all. The conclusion seems to be that an ordinary and stationary GPS receiver with a single omnidiretional antenna knows very well where satellites are relative to the true North, and where the true North is relative to satellites, but doesn't know (more precisely: can't indicate, as it lacks another reference) where satellites or the North actually are. Eventually this appears quite obvious. Antonio I8IOV You could (temporarily) install a structure that blocks reception in one direction and then infer the meridian direction from the occultation of SVs by the obstruction. However the accuracy of the determination wont be high. Bruce ___ 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] OT - GPS and North
Thanks all. The conclusion seems to be that an ordinary and stationary GPS receiver with a single omnidiretional antenna knows very well where satellites are relative to the true North, and where the true North is relative to satellites, but doesn't know (more precisely: can't indicate, as it lacks another reference) where satellites or the North actually are. Eventually this appears quite obvious. Antonio I8IOV ___ 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] OT - GPS and North
Yes, found this patent : http://www.freepatentsonline.com/y2008/0186232.html "A method and radio navigation system compass apparatus for determining true north or azimuth or orientation of a vehicle or the like by the use of integrated Loran and satellite radio navigation receivers employing crossed-loop H-field antennas for the Loran reception, or the use of at least three Loran type transmitter, or two Loran type transmitter and a synchronized clock for determining both position and azimuth. " synergy, the whole is greater than the sum of the individual parts Both GPS and loran depend on the phase/frequency/time accuracy of their source, but I wonder if other signals not as accurate but maybe short-term stable could be used to improve combined stability such as TV and radio transmitters. With such a large source of possible transmitters comparison of them to GPS and loran to pick a few good ones to add both hold-over from gps and or loran loss. For example a CDMA cell site that is dependent on GPS would slowly deteriorate if GPS was lost, but a large number of CDMA cell sites would continue to work if they could be synced to another source. Besides the hold over capability I would be interested in ways to combine as many independent sources to improve accuracy like the use of more accurate frequency sources to improve GPS accuracy: http://plan.geomatics.ucalgary.ca/papers/ENC06_Paper74_WatsonetAl_v3Web.pdf Or maybe a time-nut antidote would be better ;-) Stanley - Original Message From: Magnus Danielson mag...@rubidium.dyndns.org To: Discussion of precise time and frequency measurement Sent: Sun, November 22, 2009 11:18:58 AM Subject: Re: [time-nuts] OT - GPS and North Stanley Reynolds wrote: > Notice several of the eloran/GPS receivers advertise better than one degree > heading accuracy even when stationary. Wonder if this the result of the > sensor using an array of ferrite bar antennas or just a magnetic compass ? > > "The eLoran Heading output using Loran-C provides bearing accuracy better > than 1º, making the e-LORAN a practical alternative to more expensive heading > devices" > http://www.si-tex.com/2009description_e-loran.htm As expected: Antenna Type Active dual-loop eLoran H-field antenna with GPS patch antenna dual-loop H-field Loran antenna is expected. H-field antennas has a zero in the plane of the loop. To compensate another antenna is mounted with 90 degrees difference. Now, this allows the use of the signal from both antennas to measure the heading towards each of the LORAN stations, which together with the position can be converted to heading towards North. If the GPS receiver had two antennas with similar directional characteristics, it would too be able to do similar tricks. 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] OT - GPS and North
Stanley Reynolds wrote: Notice several of the eloran/GPS receivers advertise better than one degree heading accuracy even when stationary. Wonder if this the result of the sensor using an array of ferrite bar antennas or just a magnetic compass ? "The eLoran Heading output using Loran-C provides bearing accuracy better than 1º, making the e-LORAN a practical alternative to more expensive heading devices" http://www.si-tex.com/2009description_e-loran.htm As expected: Antenna Type Active dual-loop eLoran H-field antenna with GPS patch antenna dual-loop H-field Loran antenna is expected. H-field antennas has a zero in the plane of the loop. To compensate another antenna is mounted with 90 degrees difference. Now, this allows the use of the signal from both antennas to measure the heading towards each of the LORAN stations, which together with the position can be converted to heading towards North. If the GPS receiver had two antennas with similar directional characteristics, it would too be able to do similar tricks. 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] OT - GPS and North
Notice several of the eloran/GPS receivers advertise better than one degree heading accuracy even when stationary. Wonder if this the result of the sensor using an array of ferrite bar antennas or just a magnetic compass ? "The eLoran Heading output using Loran-C provides bearing accuracy better than 1º, making the e-LORAN a practical alternative to more expensive heading devices" http://www.si-tex.com/2009description_e-loran.htm http://www.crossrate.com/elgps1110 Stanley ___ 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] OT - GPS and North
Hi Florian, That is basicly the way it is done. The "source" is a magnetic model - a "formula" with lots of coefficients, you input your position and the output is an approximation of your magnetic declination at that position. It can be implemented by precomputing a lockup table (map) with the required bin size, or store coefficients and do the calculation in the receiver. This is actually an exact analogy with the computation of Mean Sea Level height. The GPS receiver can only measure ellipsoid height, but many receivers will output a MSL heigt, by computing or search in a precomputed "geoid separation"-map. -- Björn > Am Saturday 21 November 2009 20:32:11 schrieb J. Forster: >> OK. Sme GPS receivers have magnetic sensors. What do they do with/about >> magnetic deviation. >> > Just a wild guess: The GPS receiver also knows its location, and magnetic > deviation is known to some degree in its variation over earth's surface. > So, > why not introduce a map of magnetic deviation that basically tells you: at > location Lat; Long, your magnetic north points at 357 degrees instead of > 360. > Bingo, you're done. That would be especially useful in the pole region, > where > deviation becomes large, as the accuracy of magnetic sensors probably is > in > the order of a couple degrees. > > Sounds reasonable, doesn't it? > > HTH, > Florian > > ___ > 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] OT - GPS and North
Am Saturday 21 November 2009 20:32:11 schrieb J. Forster: > OK. Sme GPS receivers have magnetic sensors. What do they do with/about > magnetic deviation. > Just a wild guess: The GPS receiver also knows its location, and magnetic deviation is known to some degree in its variation over earth's surface. So, why not introduce a map of magnetic deviation that basically tells you: at location Lat; Long, your magnetic north points at 357 degrees instead of 360. Bingo, you're done. That would be especially useful in the pole region, where deviation becomes large, as the accuracy of magnetic sensors probably is in the order of a couple degrees. Sounds reasonable, doesn't it? HTH, Florian ___ 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] OT - GPS and North
I once went through the exercise of finding North from a station at home. A gps fix would give me +- - 1metre northing and + - 1 metre easting, another fix 1000m away would be the same, a lousy base for an accurate azimuth. Using an ephemeris for constants, a theodolite fix on a circumpolar star taken at 6 hour intervals starts to get a value with the limits being the usual limits of observing stars but less the refraction errors. I recorded the data with respect to a Referred Object, ( a street light 4 km away) Several times I repeated this exercise ( on other nights) and I was disssapointed by the precision. Now my theodolite is a Wild T1, and the method does not lend itself to getting the maximum precision from the instrument, but I was deeply impressed by the difficulty of getting an accurate measure of true North. cheers, Neville Michie On 22/11/2009, at 1:13 PM, J. Forster wrote: Not so. I'm very familiar with laying in accurate North lines for gyro testing. To get anything close to accurate (1 arc second or better) takes many hours of stellar observation with a Wild T-3 class instrument. -John === Neville Michie wrote: When you think of time specifications from GPS, the GPS system is a poor way to find north. Even with a base line of 1000 metres you only have a fraction of a degree. The GPS system may be useful to get accurate time to simplify a star observation, from a known (GPS) position on this planet, but finding north is still a problem because of the accuracy of a small number of observations from a star fix. Gyrocompasses take some time to get a measurement ( one hour) but even their estimate of North cannot match the precision that the GPS system can get us with time. cheers, Neville Michie If you are taking star shots a stellar compass can easily provide a boresight pointing accuracy of a few arcsec. Bruce ___ 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] OT - GPS and North
When a star tracker is used as a stellar compass in effect takes simultaneous fixes on several stars and the better ones are capable of an rms error of a few arc seconds, largely limited by atmospheric instability. These are usually used for determining space vehicle attitude, in which case the instability due to seeing is much smaller than when immersed in the atmosphere. They have been used as relatively inexpensive position encoders for pointing a telescope to within a few arc seconds. Pattern recognition techniques are used to identify stars in a relatively wide field (a few degrees) slightly defocused image (improves centroiding accuracy). Star tracker for Clementine mission: http://www.osti.gov/bridge/servlets/purl/86977-ULkJcR/webviewable/86977.pdf A more accurate version: http://www.newworldt.com/download/DTU/microASC%20Summary.pdf telescope pointing application: http://www.ifa.hawaii.edu/faculty/pickles/AJP/spie3351.07.pdf http://www.ifa.hawaii.edu/users/pickles/AJP/AMOS2003_v4.pdf Measuring the position (altitude + azimuth) of one star at a time using a theodolite is not the most efficient method of determining the direction of the meridian. Its far better to measure the position of several stars at once as in the stellar compass, however a longer focal length camera lens than usually used in a star tracker is desrable for increased accuracy. Bruce J. Forster wrote: Not so. I'm very familiar with laying in accurate North lines for gyro testing. To get anything close to accurate (1 arc second or better) takes many hours of stellar observation with a Wild T-3 class instrument. -John === Neville Michie wrote: When you think of time specifications from GPS, the GPS system is a poor way to find north. Even with a base line of 1000 metres you only have a fraction of a degree. The GPS system may be useful to get accurate time to simplify a star observation, from a known (GPS) position on this planet, but finding north is still a problem because of the accuracy of a small number of observations from a star fix. Gyrocompasses take some time to get a measurement ( one hour) but even their estimate of North cannot match the precision that the GPS system can get us with time. cheers, Neville Michie If you are taking star shots a stellar compass can easily provide a boresight pointing accuracy of a few arcsec. Bruce ___ 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] OT - GPS and North
Not so. I'm very familiar with laying in accurate North lines for gyro testing. To get anything close to accurate (1 arc second or better) takes many hours of stellar observation with a Wild T-3 class instrument. -John === > Neville Michie wrote: >> >> When you think of time specifications from GPS, the GPS system is a >> poor way to find north. >> Even with a base line of 1000 metres you only have a fraction of a >> degree. >> The GPS system may be useful to get accurate time to simplify a star >> observation, from a known (GPS) >> position on this planet, but finding north is still a problem because >> of the accuracy of a small >> number of observations from a star fix. >> Gyrocompasses take some time to get a measurement >> ( one hour) but even their estimate of North cannot match the >> precision that the GPS system can get us with time. >> cheers, Neville Michie > If you are taking star shots a stellar compass can easily provide a > boresight pointing accuracy of a few arcsec. > > Bruce > > > ___ > 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] OT - GPS and North
Bob Camp wrote: Hi If you only have one antenna and one receiver, the answer is fairly simple. Swing it around you head on the end of a long string. Plot the position reading vs time. Correlate the readings to the phase of the rotation. It does indeed work (it's a doppler scanner ...). You could easily argue that it's not exactly a stationary situation any more. Making it work correctly would involve a lot of work figuring out just how much lag the receiver has. You might have to swing it at a 10 rpm rate ... Putting it on a constantly rotating platform would work too. I actually made a comment about moving the antenna as an alternative to the use of multiple antennas. You can use the velocity vector in correlation with the local rotation indication to transform the local reference frame to that of the direction to north. Just swinging it around is pretty useless unless you bring that in correlation to that local reference frame. Also, you would like a fairly stable swingrate so that correlation becomes easier. Also, having a higher rate receiver, such as 10 or 20 Hz would also be nice. The PPS is a suitable reference pulse to correlate angle-measurements with that of the position given. 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] OT - GPS and North
Hi If you only have one antenna and one receiver, the answer is fairly simple. Swing it around you head on the end of a long string. Plot the position reading vs time. Correlate the readings to the phase of the rotation. It does indeed work (it's a doppler scanner ...). You could easily argue that it's not exactly a stationary situation any more. Making it work correctly would involve a lot of work figuring out just how much lag the receiver has. You might have to swing it at a 10 rpm rate ... Bob On Nov 21, 2009, at 6:59 PM, Magnus Danielson wrote: > b...@lysator.liu.se wrote: >>> Mark Spencer wrote: Would Time Difference of Arrival techniques combined with an array of four closely spaced antennas work with Gps signals as a means of determing the orentation of the antenna array vs the gps satellites ? (I'm thinking traditional TDOA techniques may not work with gps signals.) >>> There are commercial products available: >>> http://www.hemispheregps.com/Default.aspx?tabid=379 >>> http://www.hemispheregps.com/Default.aspx?tabid=412 >>> >>> >>> These devices claim less than 1 degree RMS heading accuracy. >>> >>> Here the antennas are integrated and a fixed 0.5 meter apart. They do >>> (or did) make a board that could be used with separate antennas, but I >>> can not find it right now. >>> >>> I have no idea of how the math works for computing heading. >>> >>> Gary >>> >> Any (almost) pair of GPS-receivers with phase measurement outputs can be >> used to make an attitude GPS receiver - sometimes called a GPS compass. >> You need decent antennas for good results. >> This is a special case of a phase ambiguity problem with moving base >> receiver and extremely short baseline. If the antennas are mounted at a >> fixed relative position, knowing the baseline gives a simpler problem. > > By having the additional antennas hooked to the same GPS core with multiple > frontends, the central antenna can act like a traditional receiver. The > carrier and code tracking-loops for additional antennas can then be aided by > the central antenna, which will help to reduce ambiguities. After inital > ambiguities have been resolved, maintaining tracking should not be too hard. > > Using multiple receivers does not give the same effect as tight integration. > >> I have read papers about using only one receiver and one antenna. The >> trick is then to use the antenna diagram and SNR from the currently >> tracked satellites to estimate an orientation. I have seen no commercial >> product trying this. Accuracy was not spectacular - a few degrees - if I >> remember correctly. Would need a very stable environment to work. A >> groundapplication (say car moving in urban environment) will influence the >> received SNRs to randomly to make a one antenna approach possible. > > Such an approach is indeed possible but fragile. You could also include shift > in phase center, in which case a "bad" antenna would be good. Knowing the > orientation of the antenna could allow for post-processing to compensate for > phase-shift. You would loose precission from position tracking but gain an > estimate in heading. > > 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] OT - GPS and North
Neville Michie wrote: When you think of time specifications from GPS, the GPS system is a poor way to find north. Even with a base line of 1000 metres you only have a fraction of a degree. The GPS system may be useful to get accurate time to simplify a star observation, from a known (GPS) position on this planet, but finding north is still a problem because of the accuracy of a small number of observations from a star fix. Gyrocompasses take some time to get a measurement ( one hour) but even their estimate of North cannot match the precision that the GPS system can get us with time. cheers, Neville Michie If you are taking star shots a stellar compass can easily provide a boresight pointing accuracy of a few arcsec. Bruce ___ 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] OT - GPS and North
Hi Neville > When you think of time specifications from GPS, the GPS system is a > poor way to find north. I do not understand. Please elaborate. A baseline of 10 meter will often give better than 1mrad accuracy. > Even with a base line of 1000 metres you only have a fraction of a > degree. This is just not true. > The GPS system may be useful to get accurate time to simplify a star > observation, from a known (GPS) > position on this planet, but finding north is still a problem because > of the accuracy of a small > number of observations from a star fix. > Gyrocompasses take some time to get a measurement > ( one hour) but even their estimate of North cannot match the > precision that the GPS system can get us with time. While legacy mechanical gyrocompasses on a ship, might take time to converge - it does not take a modern strapdown INS more than about 4 minutes to find north while stationary. But having 4 minutes at hand with some decent GPS-receivers its easy to get a north-measurement that will be much better than the best available intertial systems. > cheers, Neville Michie -- 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] OT - GPS and North
b...@lysator.liu.se wrote: Mark Spencer wrote: Would Time Difference of Arrival techniques combined with an array of four closely spaced antennas work with Gps signals as a means of determing the orentation of the antenna array vs the gps satellites ? (I'm thinking traditional TDOA techniques may not work with gps signals.) There are commercial products available: http://www.hemispheregps.com/Default.aspx?tabid=379 http://www.hemispheregps.com/Default.aspx?tabid=412 These devices claim less than 1 degree RMS heading accuracy. Here the antennas are integrated and a fixed 0.5 meter apart. They do (or did) make a board that could be used with separate antennas, but I can not find it right now. I have no idea of how the math works for computing heading. Gary Any (almost) pair of GPS-receivers with phase measurement outputs can be used to make an attitude GPS receiver - sometimes called a GPS compass. You need decent antennas for good results. This is a special case of a phase ambiguity problem with moving base receiver and extremely short baseline. If the antennas are mounted at a fixed relative position, knowing the baseline gives a simpler problem. By having the additional antennas hooked to the same GPS core with multiple frontends, the central antenna can act like a traditional receiver. The carrier and code tracking-loops for additional antennas can then be aided by the central antenna, which will help to reduce ambiguities. After inital ambiguities have been resolved, maintaining tracking should not be too hard. Using multiple receivers does not give the same effect as tight integration. I have read papers about using only one receiver and one antenna. The trick is then to use the antenna diagram and SNR from the currently tracked satellites to estimate an orientation. I have seen no commercial product trying this. Accuracy was not spectacular - a few degrees - if I remember correctly. Would need a very stable environment to work. A groundapplication (say car moving in urban environment) will influence the received SNRs to randomly to make a one antenna approach possible. Such an approach is indeed possible but fragile. You could also include shift in phase center, in which case a "bad" antenna would be good. Knowing the orientation of the antenna could allow for post-processing to compensate for phase-shift. You would loose precission from position tracking but gain an estimate in heading. 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] OT - GPS and North
Interesting thanks ! - Original Message From: Gary Chatters To: Discussion of precise time and frequency measurement Sent: Sat, November 21, 2009 2:57:15 PM Subject: Re: [time-nuts] OT - GPS and North Mark Spencer wrote: > Would Time Difference of Arrival techniques combined with an array of four > closely spaced antennas work with Gps signals as a means of determing the > orentation of the antenna array vs the gps satellites ? (I'm thinking > traditional TDOA techniques may not work with gps signals.) > There are commercial products available: http://www.hemispheregps.com/Default.aspx?tabid=379 http://www.hemispheregps.com/Default.aspx?tabid=412 These devices claim less than 1 degree RMS heading accuracy. Here the antennas are integrated and a fixed 0.5 meter apart. They do (or did) make a board that could be used with separate antennas, but I can not find it right now. I have no idea of how the math works for computing heading. Gary ___ 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. __ Yahoo! Canada Toolbar: Search from anywhere on the web, and bookmark your favourite sites. Download it now http://ca.toolbar.yahoo.com. ___ 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] OT - GPS and North
When you think of time specifications from GPS, the GPS system is a poor way to find north. Even with a base line of 1000 metres you only have a fraction of a degree. The GPS system may be useful to get accurate time to simplify a star observation, from a known (GPS) position on this planet, but finding north is still a problem because of the accuracy of a small number of observations from a star fix. Gyrocompasses take some time to get a measurement ( one hour) but even their estimate of North cannot match the precision that the GPS system can get us with time. cheers, Neville Michie ___ 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] OT - GPS and North
b...@lysator.liu.se wrote: J. Forster wrote: OK. Sme GPS receivers have magnetic sensors. What do they do with/about magnetic deviation. There is a field in one of the NMEA messages for magnetic deviation which some GPS receivers fill in. I do not know where they get the values. There is a mathematical model available from an appropriate agency (I forget which one right now) that can be used to compute magnetic deviation anywhere on earth. The model is supposed to be good for about five years before the coefficients need to be updated. Gary One model is called the World Magnetic Model http://en.wikipedia.org/wiki/World_Magnetic_Model That is the one I was thinking of. Follow the Wikipedia link to the NGDC webpage: http://www.ngdc.noaa.gov/geomag/WMM/ New model due 15 December. Gary ___ 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] OT - GPS and North
Iain Young wrote: Gary Chatters wrote: I have no idea of how the math works for computing heading. Checkout FORWARD and INVERSE (and their 3d equivalents) at http://www.ngs.noaa.gov/TOOLS/Inv_Fwd/Inv_Fwd.html While these are hosted on a NOAA site, I'm sure I've seen it on a NASA site as well. IIRC, there is also a C port somewhere. I am not sure that this would be useful in this application. Getting < 1 degree heading error from two positions would require about 8mm absolute accuracy. I suspect that such accuracy requires something like the phase measurements as mentioned by Björn. Gary ___ 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] OT - GPS and North
> J. Forster wrote: >> OK. Sme GPS receivers have magnetic sensors. What do they do with/about >> magnetic deviation. >> > > There is a field in one of the NMEA messages for magnetic deviation > which some GPS receivers fill in. > > I do not know where they get the values. There is a mathematical model > available from an appropriate agency (I forget which one right now) that > can be used to compute magnetic deviation anywhere on earth. The model > is supposed to be good for about five years before the coefficients need > to be updated. > > > Gary > One model is called the World Magnetic Model http://en.wikipedia.org/wiki/World_Magnetic_Model These models are the magnetic equivialent of the gravity models used to determine the geoid. -- 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] OT - GPS and North
> Mark Spencer wrote: >> Would Time Difference of Arrival techniques combined with an array of >> four closely spaced antennas work with Gps signals as a means of >> determing the orentation of the antenna array vs the gps satellites ? >> (I'm thinking traditional TDOA techniques may not work with gps >> signals.) >> > > There are commercial products available: > http://www.hemispheregps.com/Default.aspx?tabid=379 > http://www.hemispheregps.com/Default.aspx?tabid=412 > > > These devices claim less than 1 degree RMS heading accuracy. > > Here the antennas are integrated and a fixed 0.5 meter apart. They do > (or did) make a board that could be used with separate antennas, but I > can not find it right now. > > I have no idea of how the math works for computing heading. > > Gary > Any (almost) pair of GPS-receivers with phase measurement outputs can be used to make an attitude GPS receiver - sometimes called a GPS compass. You need decent antennas for good results. This is a special case of a phase ambiguity problem with moving base receiver and extremely short baseline. If the antennas are mounted at a fixed relative position, knowing the baseline gives a simpler problem. I have read papers about using only one receiver and one antenna. The trick is then to use the antenna diagram and SNR from the currently tracked satellites to estimate an orientation. I have seen no commercial product trying this. Accuracy was not spectacular - a few degrees - if I remember correctly. Would need a very stable environment to work. A groundapplication (say car moving in urban environment) will influence the received SNRs to randomly to make a one antenna approach possible. Most GPS manufacturers have attitude GPS receivers. If not dedicated its a special case for their RTK capable versions. -- 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] OT - GPS and North
Gary Chatters wrote: I have no idea of how the math works for computing heading. Checkout FORWARD and INVERSE (and their 3d equivalents) at http://www.ngs.noaa.gov/TOOLS/Inv_Fwd/Inv_Fwd.html While these are hosted on a NOAA site, I'm sure I've seen it on a NASA site as well. IIRC, there is also a C port somewhere. Iain ___ 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] OT - GPS and North
J. Forster wrote: OK. Sme GPS receivers have magnetic sensors. What do they do with/about magnetic deviation. There is a field in one of the NMEA messages for magnetic deviation which some GPS receivers fill in. I do not know where they get the values. There is a mathematical model available from an appropriate agency (I forget which one right now) that can be used to compute magnetic deviation anywhere on earth. The model is supposed to be good for about five years before the coefficients need to be updated. Gary ___ 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] OT - GPS and North
Gary Chatters wrote: Mark Spencer wrote: Would Time Difference of Arrival techniques combined with an array of four closely spaced antennas work with Gps signals as a means of determing the orentation of the antenna array vs the gps satellites ? (I'm thinking traditional TDOA techniques may not work with gps signals.) There are commercial products available: http://www.hemispheregps.com/Default.aspx?tabid=379 http://www.hemispheregps.com/Default.aspx?tabid=412 These devices claim less than 1 degree RMS heading accuracy. Here the antennas are integrated and a fixed 0.5 meter apart. They do (or did) make a board that could be used with separate antennas, but I can not find it right now. I think this is the one: http://www.hemispheregps.com/Products/PrecisionProductsGroup/PrecisionProducts/CrescentOEMModules/tabid/136/Default.aspx I have no idea of how the math works for computing heading. ___ 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] OT - GPS and North
Mark Spencer wrote: Would Time Difference of Arrival techniques combined with an array of four closely spaced antennas work with Gps signals as a means of determing the orentation of the antenna array vs the gps satellites ? (I'm thinking traditional TDOA techniques may not work with gps signals.) There are commercial products available: http://www.hemispheregps.com/Default.aspx?tabid=379 http://www.hemispheregps.com/Default.aspx?tabid=412 These devices claim less than 1 degree RMS heading accuracy. Here the antennas are integrated and a fixed 0.5 meter apart. They do (or did) make a board that could be used with separate antennas, but I can not find it right now. I have no idea of how the math works for computing heading. Gary ___ 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] OT - GPS and North
Tom, this would be taking advantage of the irregularities of the GPS receive antenna to determine the orientation of the antenna. For example, if the GPS antenna were a Yagi, and it was pointed with the major lobe in an Easterly direction, when you listen to a satellite in the East, you know it's location and you can observe a high signal strength. A satellite in the West might have a low signal strength, or be missing. Now this thought experiment is loaded with issues; for example, external attenuation, multi-path, multiple lobes, small gain differences, etc., but we're just having fun here. Mike - AA8K Tom Van Baak wrote: Mike, The calculations tell you where on the globe you are. Correct, from this you can easily calculate angle and distance to either pole. But the receiver cannot "indicate" this angle. Meaning if you hold a GPS antenna in your hand you may know you have to aim 75 degrees and walk 5000 km to the North pole but you still have no idea how to turn around to take that first step. A static GPS receiver is a point device, not a pointing device. On the other hand a magnetic compass is a pointing device, not a point device. That's why some navigation units combine both. If you just want to travel then as Confucius say: journey of a thousand miles begins with single step. But if you want to reach a particular destination then journey of a thousand miles must begin with single step in correct direction. ;-) /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] OT - GPS and North
Clearly, two three antennas can tell you everything you need to know. I've seen video of a model helicopter flying itself with three GPS antennas. NASA, I think. -John === > Would Time Difference of Arrival techniques combined with an array of four > closely spaced antennas work with Gps signals as a means of determing the > orentation of the antenna array vs the gps satellites ? (I'm thinking > traditional TDOA techniques may not work with gps signals.) ___ 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] OT - GPS and North
OK. Sme GPS receivers have magnetic sensors. What do they do with/about magnetic deviation. -John == > Tom Van Baak wrote: >>> Does a stationary (not in motion) GPS receiver know where the North is? >> >> No, a stationary object is a point, not a line or a vector. >> The notion of North (or any direction) has no meaning >> to a point, by definition. > > You are mixing things a litte too much here. There is no direction > within a 0-dimensional space, but a point as it is positioned in a > 3-dimensional space has no problem to have an associated vector pointing > either to a location or along some field such as the magnetic field. > > An electron is a point-charge, and reacts to a magnetic field or the > electrostatic field. > > The antenna is certainly not a point, it is a sizeable object and it's > phase centrum isn't a point either, it's just a handy approximation. > > It's just that normal GPS antennas and receivers isn't built for this > purpose. A much smaller object than either the antenna or the receiver > is the SO-8 packaged magnetic sensor you can buy cheaply and sense the > magnetic field. A GPS receiver can be used to compensate for magnetic > deviation if needed. > > 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] OT - GPS and North
Would Time Difference of Arrival techniques combined with an array of four closely spaced antennas work with Gps signals as a means of determing the orentation of the antenna array vs the gps satellites ? (I'm thinking traditional TDOA techniques may not work with gps signals.) Mike Naruta AA8K wrote: > Yes, but it is rather difficult to manufacture an > isotropic antenna. Unless the antenna is oriented > so as to present a normal hemisphere of same gain, > it might be theoretically possible to model the gain > versus direction, coupled with the knowledge of > location of satellites and received strength, to > determine the antenna's orientation with respect > to the world. > Now, there are lots of sources of error and > potential ambiguities for this process. As > you say, it is more straightforward to use a > magnetic field sensor. With position information > it should be easy to correct for true North. > Mike - AA8K > Magnus Danielson wrote: >> >> Yes, but you don't know in what direction from the unidirectional antenna. >> The antenna has no sense of direction, but the receiver knows very well in >> what direction relative north each sat is. The NMEA stream even include the >> coarse directions. >> >> If you has a steerable directional antenna, several antennas or moveable >> antenna, then you can convert the internal directions of the antenna into a >> north heading or heading towards anything else. >> >> But a normal unidirectional GPS antenna and associated receiver will be able >> to know where it is and from it provide very high precision direction >> relative north, but unless you move it or make any other form of aid, it >> will not be able to show the heading... but when you move around in with the >> car, then it can show it relative to the current heading of the car... as >> that forms a vector for which you can relate an angle... to north or to your >> intended destination. >> >> 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. __ Yahoo! Canada Toolbar: Search from anywhere on the web, and bookmark your favourite sites. Download it now http://ca.toolbar.yahoo.com. ___ 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] OT - GPS and North
If the positions of the satellites are known, as they must be to enable the antennas position to be calculated, I think just an extra set of calculations is necessary to indicate the direction to anywhere else on the planet (or elsewhere) including the geographic poles. Mike, The calculations tell you where on the globe you are. Correct, from this you can easily calculate angle and distance to either pole. But the receiver cannot "indicate" this angle. Meaning if you hold a GPS antenna in your hand you may know you have to aim 75 degrees and walk 5000 km to the North pole but you still have no idea how to turn around to take that first step. A static GPS receiver is a point device, not a pointing device. On the other hand a magnetic compass is a pointing device, not a point device. That's why some navigation units combine both. If you just want to travel then as Confucius say: journey of a thousand miles begins with single step. But if you want to reach a particular destination then journey of a thousand miles must begin with single step in correct direction. ;-) /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] OT - GPS and North
Yes, but it is rather difficult to manufacture an isotropic antenna. Unless the antenna is oriented so as to present a normal hemisphere of same gain, it might be theoretically possible to model the gain versus direction, coupled with the knowledge of location of satellites and received strength, to determine the antenna's orientation with respect to the world. Now, there are lots of sources of error and potential ambiguities for this process. As you say, it is more straightforward to use a magnetic field sensor. With position information it should be easy to correct for true North. Mike - AA8K Magnus Danielson wrote: Yes, but you don't know in what direction from the unidirectional antenna. The antenna has no sense of direction, but the receiver knows very well in what direction relative north each sat is. The NMEA stream even include the coarse directions. If you has a steerable directional antenna, several antennas or moveable antenna, then you can convert the internal directions of the antenna into a north heading or heading towards anything else. But a normal unidirectional GPS antenna and associated receiver will be able to know where it is and from it provide very high precision direction relative north, but unless you move it or make any other form of aid, it will not be able to show the heading... but when you move around in with the car, then it can show it relative to the current heading of the car... as that forms a vector for which you can relate an angle... to north or to your intended destination. 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] OT - GPS and North
mike cook wrote: - Original Message - From: "Magnus Danielson" To: "Discussion of precise time and frequency measurement" Sent: Saturday, November 21, 2009 4:05 PM Subject: Re: [time-nuts] OT - GPS and North Robert Darlington wrote: It depends on the GPS receiver. The GPS chipset won't know (it knows where it is and can remember where it was to know what direction it's moving), but some consumer GPS receivers (Garmin, Magellan) have electronic compasses built in. My Garmin eTrex Legend does NOT have a compass built in, but taking about 2 steps in any direction will tell me which way I'm moving. It can't do this when stationary. My buddy's eTrex can point north without moving, but that feature drains the battery faster. The actual GPS receiver and the navigator is two different things. A GPS navigator may use additional sensors such as accelerometers and magnetic sensor to aid in addition to the GPS receiver built into them. Agreed Magnus, but I dont think any gizmos are required. If the the positions of the satellites are known, as they must be to enable the antennas position to be calculated, I think just an extra set of calculations is necessary to indicate the direction to anywhere else on the planet (or elsewhere) including the geographic poles. Getting the magnetic pole directions would need something else I suppose. Yes, but you don't know in what direction from the unidirectional antenna. The antenna has no sense of direction, but the receiver knows very well in what direction relative north each sat is. The NMEA stream even include the coarse directions. If you has a steerable directional antenna, several antennas or moveable antenna, then you can convert the internal directions of the antenna into a north heading or heading towards anything else. But a normal unidirectional GPS antenna and associated receiver will be able to know where it is and from it provide very high precision direction relative north, but unless you move it or make any other form of aid, it will not be able to show the heading... but when you move around in with the car, then it can show it relative to the current heading of the car... as that forms a vector for which you can relate an angle... to north or to your intended destination. 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] OT - GPS and North
Tom Van Baak wrote: Does a stationary (not in motion) GPS receiver know where the North is? No, a stationary object is a point, not a line or a vector. The notion of North (or any direction) has no meaning to a point, by definition. You are mixing things a litte too much here. There is no direction within a 0-dimensional space, but a point as it is positioned in a 3-dimensional space has no problem to have an associated vector pointing either to a location or along some field such as the magnetic field. An electron is a point-charge, and reacts to a magnetic field or the electrostatic field. The antenna is certainly not a point, it is a sizeable object and it's phase centrum isn't a point either, it's just a handy approximation. It's just that normal GPS antennas and receivers isn't built for this purpose. A much smaller object than either the antenna or the receiver is the SO-8 packaged magnetic sensor you can buy cheaply and sense the magnetic field. A GPS receiver can be used to compensate for magnetic deviation if needed. 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] OT - GPS and North
> Agreed Magnus, but I dont think any gizmos are required. If the the > positions of the satellites are known, as they must be to enable the > antennas position to be calculated, I think just an extra set of > calculations is necessary to indicate the direction to anywhere else > on the planet (or elsewhere) including the geographic poles. Getting > the magnetic pole directions would need something else I suppose. I think that only works if your antenna is bigger than a point source. Consider the simple case of a car radio. Which way is the transmitter? If you have a directional antenna, say a yagi or dish for your TV, you can figure out what direction the signal is coming from by rotating the antenna and measuring the signal strength. With multiple antennas you can use phased array techniques. -- These are my opinions, not necessarily my employer's. I hate spam. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] OT - GPS and North
- Original Message - From: "Magnus Danielson" To: "Discussion of precise time and frequency measurement" Sent: Saturday, November 21, 2009 4:05 PM Subject: Re: [time-nuts] OT - GPS and North Robert Darlington wrote: It depends on the GPS receiver. The GPS chipset won't know (it knows where it is and can remember where it was to know what direction it's moving), but some consumer GPS receivers (Garmin, Magellan) have electronic compasses built in. My Garmin eTrex Legend does NOT have a compass built in, but taking about 2 steps in any direction will tell me which way I'm moving. It can't do this when stationary. My buddy's eTrex can point north without moving, but that feature drains the battery faster. The actual GPS receiver and the navigator is two different things. A GPS navigator may use additional sensors such as accelerometers and magnetic sensor to aid in addition to the GPS receiver built into them. Agreed Magnus, but I dont think any gizmos are required. If the the positions of the satellites are known, as they must be to enable the antennas position to be calculated, I think just an extra set of calculations is necessary to indicate the direction to anywhere else on the planet (or elsewhere) including the geographic poles. Getting the magnetic pole directions would need something else I suppose. So a navigator may know, even if on a fixed location, but the GPS receiver does not have that information. It is important to keep these separated so that they can be discussed properly. I don't want to say stuff like "The actual GPS receiver in the GPS receiver...". 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] OT - GPS and North
Does a stationary (not in motion) GPS receiver know where the North is? No, a stationary object is a point, not a line or a vector. The notion of North (or any direction) has no meaning to a point, by definition. There are two exceptions. If during your long polar trek the latitude is ±90º 00' 00.0" and the longitude seems to wander all over the map then, yes, your stationary GPS receiver finally knows where North is. Examples: http://www.klipsi.ch/at_Northpole/at_Northpole.htm http://www.icetent.com/south_pole.htm http://www.4x4offroads.com/south-pole-expedition-world-record.html /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] OT - GPS and North
Am Saturday 21 November 2009 15:05:12 schrieb iov...@inwind.it: > Does a stationary (not in motion) GPS receiver know where the North is? > > As far > as I can understand, it doesn't, isn't it? > Umm, as far as i understand it, a single receiver with a single omnidirectional antenna (at least with rotational symmetry around the vertical axis) can't know where north is. IF you just so happen to have a more clever setup, this indeed becomes possible. Basically, a GPS receiver happens to not compute his own location but the one of his antenna. So if you happen to have a receiver with enough correlators and stuff to properly connect two (or more) antennas and calculate positions for both, it could actually deduce true north. Bearings get better the more space you have between the antennas and the more averaging you can apply. Time for averaging doesn't seem much of an issue in a truly stationary setup, so just try to maximize separation of your antennas. HTH, Florian ___ 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] OT - GPS and North
Robert Darlington wrote: It depends on the GPS receiver. The GPS chipset won't know (it knows where it is and can remember where it was to know what direction it's moving), but some consumer GPS receivers (Garmin, Magellan) have electronic compasses built in. My Garmin eTrex Legend does NOT have a compass built in, but taking about 2 steps in any direction will tell me which way I'm moving. It can't do this when stationary. My buddy's eTrex can point north without moving, but that feature drains the battery faster. The actual GPS receiver and the navigator is two different things. A GPS navigator may use additional sensors such as accelerometers and magnetic sensor to aid in addition to the GPS receiver built into them. So a navigator may know, even if on a fixed location, but the GPS receiver does not have that information. It is important to keep these separated so that they can be discussed properly. I don't want to say stuff like "The actual GPS receiver in the GPS receiver...". 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] OT - GPS and North
It depends on the GPS receiver. The GPS chipset won't know (it knows where it is and can remember where it was to know what direction it's moving), but some consumer GPS receivers (Garmin, Magellan) have electronic compasses built in. My Garmin eTrex Legend does NOT have a compass built in, but taking about 2 steps in any direction will tell me which way I'm moving. It can't do this when stationary. My buddy's eTrex can point north without moving, but that feature drains the battery faster. -Bob On Sat, Nov 21, 2009 at 7:05 AM, iov...@inwind.it wrote: > Does a stationary (not in motion) GPS receiver know where the North is? > > As far > as I can understand, it doesn't, isn't it? > > Antonio I8IOV > > ___ > 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] OT - GPS and North
iov...@inwind.it wrote: Does a stationary (not in motion) GPS receiver know where the North is? As far as I can understand, it doesn't, isn't it? Not one with a unidirectional antenna, which is the usual stuff. If you have multiple antennas you can sort out the directions. But it is an expensive way of achieving it. If your antenna moves you can detect the heading relative north. A sensor to sense the magnetic field is fairly inexpensive so that is being used. 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] OT - GPS and North
That is an interesting question. It could be possible if it had two antennas or its antenna was not omni-directional. Mike - AA8K iov...@inwind.it wrote: Does a stationary (not in motion) GPS receiver know where the North is? As far as I can understand, it doesn't, isn't it? Antonio I8IOV ___ 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] OT - GPS and North
Does a stationary (not in motion) GPS receiver know where the North is? As far as I can understand, it doesn't, isn't it? Antonio I8IOV ___ 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.
