Delay of the complete ensemble of signals results in a time shift much like the addition of cable between the antenna and receiver. The position solution will be the location of the first receiving antenna. John WA4WDL -------------------------------------------------- From: "MailLists" <lists@medesign.ro> Sent: Thursday, April 12, 2012 10:17 AM To: "Discussion of precise time and frequency measurement" <time-nuts@febo.com> Subject: Re: [time-nuts] Re-radiating a GPS signal...?? > GPS being extremely time-dependent, any delay introduced will affect > positioning precision.

 ``Please note: re-radiation kits are currently only
 available for purchase to International Customers and in
 cases where the U.S. Government is the end user.''


 Pursuant to Section 15.201(b) of the Rules, 47 C.F.R. §

 You should be aware that the Commission has recently

You must read: http://transition.fcc.gov/eb/Orders/2005/DA-05-2998A1.html Which discusses a FCC complaint with Navtech for selling GPS repeaters. An exert is presented below: ``Please note: re-radiation kits are currently only available for purchase to International Customers and in cases where the U.S. Government is the end user.'' Pursuant to Section 15.201(b) of the Rules, 47 C.F.R. § 15.201(b), intentional radiators must be authorized in accordance with the FCC's certification procedures prior to the initiation of marketing in the United States. However, GPS re-radiators operate within the restricted frequency bands listed in Section 15.205(a) of the Rules, 47 C.F.R. § 15.205(a).4 Thus, GPS re- radiators cannot comply with the FCC's technical standards and therefore cannot be certificated or marketed for use by the general public or non-federal government entities. Accordingly, it appears that Navtech has violated Section 302(b) of the Act and Sections 2.803 and 15.205(a) of the Rules by marketing in the United States radio frequency devices that are not eligible to receive a grant of certification. You should be aware that the Commission has recently addressed a Petition for Rulemaking and a Request for Waiver seeking amendment of FCC regulations to permit the marketing of GPS re-radiation kits.5 By Order released July 6, 2005, the FCC's Office of Engineering and Technology (OET) denied the Petition for Rulemaking and Request for Waiver.6 OET noted that the Petition raised significant issues that needed further study and therefore did not warrant consideration at the time. Accordingly, Navtech is reminded that at this time GPS re- radiating devices are not permitted to be sold to the general public or to state or local governments. John WA4WDL

Björn

Purely geometrically, the fix solution is computed as the intersection point of spheres with the radii determined by the propagation time, and the centers by the positions of the satellites (practically not all spheres intersect in the same geometrical point, so an average is computed). If the GPS Rx would receive simultaneously all satellites, considered evenly distributed on a sphere, then the added path delays would mostly cancel out - but if only the visible satellites are accounted for, we will have an unbalanced system, approximated to an hemispehere, in which the horizontal error will be low, as the longer paths cancel mostly out, but for the vertical one it's not the case. Any GPS receiver will exhibit lower vertical precision than the horizontal one. The same phenomenon, of low precision, and biasing of position is evident if just a part of the constellation is used (an obstacle obscures a large part of the sky). The internal delays of the Rx are mostly fixed and known, so they can be accounted for, and compensated in the firmware fix solution, but the cable length is a variable (depending on the installation) factor, not accounted for. On 4/12/2012 7:15 PM, bg@lysator.liu.se wrote: > Not at all! > > The (first) receiving antenna defines the position you get out of a long > antenna cable or a reradiating system. The delays in LNA, filters, cables, > rerad antenna, free air between rerad antenna and final receiving antenna > ALL goed into the receiver clock error. This is clear both from a > theoretical point, from most standard GPS texts and from practical > experience from multiple installations I have used over the years. > > If you disagree, please provide evidence. > > -- > > Björn > >> Not quite, the delay of the antenna cable is affecting less the >> horizontal position (it depends also on the current received >> constellation geometry), but mostly the height ASL of the fix point, >> prolonging simultaneously all the paths from the satellites with a fixed >> value. >> Also, the propagation speed in a cable is significantly lower than in >> free space - the perceived delay increase is ~1.5 times for usual cables >> (~.67 velocity factor), and the computed fix point would have a lower >> height ASL than the real one. >> >> Those relaying systems are merely good for an approximate location fix, >> mostly for not loosing the GPS signal in covered areas so that the >> reacquire of the real signal is faster, with almost no perceived >> discontinuity. >> >> >> On 4/12/2012 6:11 PM, David McGaw wrote: >>> The time/position fix would be from the location of the receiving >>> antenna of the repeater, degraded only by noise. >>> >>> This should work if both antennas have good back-side rejection >>> (choke-rings are particularly good for this but perhaps any good timing >>> antenna could meet this), the re-transmitting antenna is close to being >>> directly under the receiving antenna, and the system gain is low enough. >>> The problem I would see in a room that is not fully shielded is >>> interference between the direct and retransmitted signals at the >>> receiver under test. >>> >>> David N1HAC >>> >>> On 4/12/12 10:17 AM, MailLists wrote: >>>> GPS being extremely time-dependent, any delay introduced will affect >>>> positioning precision. Also, the signal is too weak for such an >>>> amplification/echo cancelling signal chain. >>>> Passive relaying, or using at most a simple amplifier with low enough >>>> gain, and short signal delay, remain the only feasible concepts. >>>> >>>> On 4/12/2012 4:48 PM, Azelio Boriani wrote: >>>>> Passive UHF TV repeaters were in use in Italy too. Nowadays, for the >>>>> DVB-T >>>>> TV, active gap-fillers are used instead. Active gap-fillers are >>>>> same-channel repeaters with the necessary, sophisticated echo >>>>> suppression >>>>> technique. We have developed our echo suppression signal processor on >>>>> a >>>>> Xilinx Virtex5 FPGA: maybe something similar may be done for the GPS >>>>> CDMA. >>>>> >>>>> On Thu, Apr 12, 2012 at 3:29 PM, Alan >>>>> Melia<alan.melia@btinternet.com>wrote: >>>>> >>>>>> If the isolation is good and the "clear view" signal is reasonably >>>>>> strong, >>>>>> the passive system works well in hangers, metalclad warehouses, >>>>>> ferry lorry >>>>>> decks. >>>>>> The passive system in the UK used to be refered to as the "Matlock >>>>>> Repeater". >>>>>> >>>>>> Alan >>>>>> G3NYK >>>>>> >>>>>> ----- Original Message ----- >>>>>> From: "Michael Baker"<mpb45@clanbaker.org> >>>>>> To:<time-nuts@febo.com> >>>>>> Sent: Thursday, April 12, 2012 2:05 PM >>>>>> Subject: [time-nuts] Re-radiating a GPS signal...?? >>>>>> >>>>>> >>>>>>> Time-nutters-- >>>>>>> >>>>>>> So-- How do GPS signal re-radiators work? >>>>>>> >>>>>>> How do you place a GPS antenna on top of a building, >>>>>>> pick up the signal with an LNA, amplify it to re-transmit >>>>>>> on an inside antenna without the amplified re-transmitted >>>>>>> signal getting back into the roof-top receiving antenna? >>>>>>> >>>>>>> I can see circumstances where a huge metal building >>>>>>> (aircraft hangar?) might provide enough isolation to >>>>>>> prevent problems, but in many cases I wonder about it... >>>>>>> ---------------------------- >>>>>>> >>>>>>> As an aside note-- I recall seeing, many years ago, a totally >>>>>>> passive TV signal repeater on top of a tall hill in mountainous >>>>>>> territory relaying a TV station signal to some homes in a valley >>>>>>> just below. The passive repeater consisted of an array of >>>>>>> high-gain UHF yagis pointing to the 40 mile distant TV station >>>>>>> tower. >>>>>>> The yagi array was coupled to another set of high-gain yagi >>>>>>> antennas pointing down to the homesites in the valley. I was >>>>>>> told that it worked pretty well. >>>>>>> >>>>>>> Mike Baker >>>>>>> ---------------------- >>>>>>> >>>>>>> _______________________________________________ >>>>>>> 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. >> >> _______________________________________________ >> 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.

Björn

Since I am used to figuring the cable (and additional propagation) delays, I did forget to mention that for timing. :-) On the other hand, I would not be using a repeater except for just functional testing of a payload system. David On 4/12/12 12:15 PM, bg@lysator.liu.se wrote: > Not at all! > > The (first) receiving antenna defines the position you get out of a long > antenna cable or a reradiating system. The delays in LNA, filters, cables, > rerad antenna, free air between rerad antenna and final receiving antenna > ALL goed into the receiver clock error. This is clear both from a > theoretical point, from most standard GPS texts and from practical > experience from multiple installations I have used over the years. > > If you disagree, please provide evidence. > > -- > > Björn > >> Not quite, the delay of the antenna cable is affecting less the >> horizontal position (it depends also on the current received >> constellation geometry), but mostly the height ASL of the fix point, >> prolonging simultaneously all the paths from the satellites with a fixed >> value. >> Also, the propagation speed in a cable is significantly lower than in >> free space - the perceived delay increase is ~1.5 times for usual cables >> (~.67 velocity factor), and the computed fix point would have a lower >> height ASL than the real one. >> >> Those relaying systems are merely good for an approximate location fix, >> mostly for not loosing the GPS signal in covered areas so that the >> reacquire of the real signal is faster, with almost no perceived >> discontinuity. >> >> >> On 4/12/2012 6:11 PM, David McGaw wrote: >>> The time/position fix would be from the location of the receiving >>> antenna of the repeater, degraded only by noise. >>> >>> This should work if both antennas have good back-side rejection >>> (choke-rings are particularly good for this but perhaps any good timing >>> antenna could meet this), the re-transmitting antenna is close to being >>> directly under the receiving antenna, and the system gain is low enough. >>> The problem I would see in a room that is not fully shielded is >>> interference between the direct and retransmitted signals at the >>> receiver under test. >>> >>> David N1HAC >>> >>> On 4/12/12 10:17 AM, MailLists wrote: >>>> GPS being extremely time-dependent, any delay introduced will affect >>>> positioning precision. Also, the signal is too weak for such an >>>> amplification/echo cancelling signal chain. >>>> Passive relaying, or using at most a simple amplifier with low enough >>>> gain, and short signal delay, remain the only feasible concepts. >>>> >>>> On 4/12/2012 4:48 PM, Azelio Boriani wrote: >>>>> Passive UHF TV repeaters were in use in Italy too. Nowadays, for the >>>>> DVB-T >>>>> TV, active gap-fillers are used instead. Active gap-fillers are >>>>> same-channel repeaters with the necessary, sophisticated echo >>>>> suppression >>>>> technique. We have developed our echo suppression signal processor on >>>>> a >>>>> Xilinx Virtex5 FPGA: maybe something similar may be done for the GPS >>>>> CDMA. >>>>> >>>>> On Thu, Apr 12, 2012 at 3:29 PM, Alan >>>>> Melia<alan.melia@btinternet.com>wrote: >>>>> >>>>>> If the isolation is good and the "clear view" signal is reasonably >>>>>> strong, >>>>>> the passive system works well in hangers, metalclad warehouses, >>>>>> ferry lorry >>>>>> decks. >>>>>> The passive system in the UK used to be refered to as the "Matlock >>>>>> Repeater". >>>>>> >>>>>> Alan >>>>>> G3NYK >>>>>> >>>>>> ----- Original Message ----- >>>>>> From: "Michael Baker"<mpb45@clanbaker.org> >>>>>> To:<time-nuts@febo.com> >>>>>> Sent: Thursday, April 12, 2012 2:05 PM >>>>>> Subject: [time-nuts] Re-radiating a GPS signal...?? >>>>>> >>>>>> >>>>>>> Time-nutters-- >>>>>>> >>>>>>> So-- How do GPS signal re-radiators work? >>>>>>> >>>>>>> How do you place a GPS antenna on top of a building, >>>>>>> pick up the signal with an LNA, amplify it to re-transmit >>>>>>> on an inside antenna without the amplified re-transmitted >>>>>>> signal getting back into the roof-top receiving antenna? >>>>>>> >>>>>>> I can see circumstances where a huge metal building >>>>>>> (aircraft hangar?) might provide enough isolation to >>>>>>> prevent problems, but in many cases I wonder about it... >>>>>>> ---------------------------- >>>>>>> >>>>>>> As an aside note-- I recall seeing, many years ago, a totally >>>>>>> passive TV signal repeater on top of a tall hill in mountainous >>>>>>> territory relaying a TV station signal to some homes in a valley >>>>>>> just below. The passive repeater consisted of an array of >>>>>>> high-gain UHF yagis pointing to the 40 mile distant TV station >>>>>>> tower. >>>>>>> The yagi array was coupled to another set of high-gain yagi >>>>>>> antennas pointing down to the homesites in the valley. I was >>>>>>> told that it worked pretty well. >>>>>>> >>>>>>> Mike Baker >>>>>>> ---------------------- >>>>>>> >>>>>>> _______________________________________________ >>>>>>> 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. >> _______________________________________________ >> 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.

Timing GPS receivers have the cable delay parameter to account for the cable delay. >>added path delays would mostly cancel out How can delays cancel out? On Thu, Apr 12, 2012 at 7:33 PM, MailLists <lists@medesign.ro> wrote: > Purely geometrically, the fix solution is computed as the intersection > point of spheres with the radii determined by the propagation time, and the > centers by the positions of the satellites (practically not all spheres > intersect in the same geometrical point, so an average is computed). > If the GPS Rx would receive simultaneously all satellites, considered > evenly distributed on a sphere, then the added path delays would mostly > cancel out - but if only the visible satellites are accounted for, we will > have an unbalanced system, approximated to an hemispehere, in which the > horizontal error will be low, as the longer paths cancel mostly out, but > for the vertical one it's not the case. > > Any GPS receiver will exhibit lower vertical precision than the horizontal > one. > The same phenomenon, of low precision, and biasing of position is evident > if just a part of the constellation is used (an obstacle obscures a large > part of the sky). > > The internal delays of the Rx are mostly fixed and known, so they can be > accounted for, and compensated in the firmware fix solution, but the cable > length is a variable (depending on the installation) factor, not accounted > for. > > > On 4/12/2012 7:15 PM, bg@lysator.liu.se wrote: > >> Not at all! >> >> The (first) receiving antenna defines the position you get out of a long >> antenna cable or a reradiating system. The delays in LNA, filters, cables, >> rerad antenna, free air between rerad antenna and final receiving antenna >> ALL goed into the receiver clock error. This is clear both from a >> theoretical point, from most standard GPS texts and from practical >> experience from multiple installations I have used over the years. >> >> If you disagree, please provide evidence. >> >> -- >> >> Björn >> >> Not quite, the delay of the antenna cable is affecting less the >>> horizontal position (it depends also on the current received >>> constellation geometry), but mostly the height ASL of the fix point, >>> prolonging simultaneously all the paths from the satellites with a fixed >>> value. >>> Also, the propagation speed in a cable is significantly lower than in >>> free space - the perceived delay increase is ~1.5 times for usual cables >>> (~.67 velocity factor), and the computed fix point would have a lower >>> height ASL than the real one. >>> >>> Those relaying systems are merely good for an approximate location fix, >>> mostly for not loosing the GPS signal in covered areas so that the >>> reacquire of the real signal is faster, with almost no perceived >>> discontinuity. >>> >>> >>> On 4/12/2012 6:11 PM, David McGaw wrote: >>> >>>> The time/position fix would be from the location of the receiving >>>> antenna of the repeater, degraded only by noise. >>>> >>>> This should work if both antennas have good back-side rejection >>>> (choke-rings are particularly good for this but perhaps any good timing >>>> antenna could meet this), the re-transmitting antenna is close to being >>>> directly under the receiving antenna, and the system gain is low enough. >>>> The problem I would see in a room that is not fully shielded is >>>> interference between the direct and retransmitted signals at the >>>> receiver under test. >>>> >>>> David N1HAC >>>> >>>> On 4/12/12 10:17 AM, MailLists wrote: >>>> >>>>> GPS being extremely time-dependent, any delay introduced will affect >>>>> positioning precision. Also, the signal is too weak for such an >>>>> amplification/echo cancelling signal chain. >>>>> Passive relaying, or using at most a simple amplifier with low enough >>>>> gain, and short signal delay, remain the only feasible concepts. >>>>> >>>>> On 4/12/2012 4:48 PM, Azelio Boriani wrote: >>>>> >>>>>> Passive UHF TV repeaters were in use in Italy too. Nowadays, for the >>>>>> DVB-T >>>>>> TV, active gap-fillers are used instead. Active gap-fillers are >>>>>> same-channel repeaters with the necessary, sophisticated echo >>>>>> suppression >>>>>> technique. We have developed our echo suppression signal processor on >>>>>> a >>>>>> Xilinx Virtex5 FPGA: maybe something similar may be done for the GPS >>>>>> CDMA. >>>>>> >>>>>> On Thu, Apr 12, 2012 at 3:29 PM, Alan >>>>>> Melia<alan.melia@btinternet.com>wrote: >>>>>> >>>>>> If the isolation is good and the "clear view" signal is reasonably >>>>>>> strong, >>>>>>> the passive system works well in hangers, metalclad warehouses, >>>>>>> ferry lorry >>>>>>> decks. >>>>>>> The passive system in the UK used to be refered to as the "Matlock >>>>>>> Repeater". >>>>>>> >>>>>>> Alan >>>>>>> G3NYK >>>>>>> >>>>>>> ----- Original Message ----- >>>>>>> From: "Michael Baker"<mpb45@clanbaker.org> >>>>>>> To:<time-nuts@febo.com> >>>>>>> Sent: Thursday, April 12, 2012 2:05 PM >>>>>>> Subject: [time-nuts] Re-radiating a GPS signal...?? >>>>>>> >>>>>>> >>>>>>> Time-nutters-- >>>>>>>> >>>>>>>> So-- How do GPS signal re-radiators work? >>>>>>>> >>>>>>>> How do you place a GPS antenna on top of a building, >>>>>>>> pick up the signal with an LNA, amplify it to re-transmit >>>>>>>> on an inside antenna without the amplified re-transmitted >>>>>>>> signal getting back into the roof-top receiving antenna? >>>>>>>> >>>>>>>> I can see circumstances where a huge metal building >>>>>>>> (aircraft hangar?) might provide enough isolation to >>>>>>>> prevent problems, but in many cases I wonder about it... >>>>>>>> ---------------------------- >>>>>>>> >>>>>>>> As an aside note-- I recall seeing, many years ago, a totally >>>>>>>> passive TV signal repeater on top of a tall hill in mountainous >>>>>>>> territory relaying a TV station signal to some homes in a valley >>>>>>>> just below. The passive repeater consisted of an array of >>>>>>>> high-gain UHF yagis pointing to the 40 mile distant TV station >>>>>>>> tower. >>>>>>>> The yagi array was coupled to another set of high-gain yagi >>>>>>>> antennas pointing down to the homesites in the valley. I was >>>>>>>> told that it worked pretty well. >>>>>>>> >>>>>>>> Mike Baker >>>>>>>> ---------------------- >>>>>>>> >>>>>>>> _______________________________________________ >>>>>>>> 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. >>>>> >>>> >>> _______________________________________________ >>> 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. >

Yes, but the propagation times are the times from each satellite antenna phase center to the phase center of the receiving antenna. From that point forward, the relative time delays are unchanged. It is the same as if one was to record the RF signals at the back of the receiving antenna and then play the recording into a receiver a week later. The navigation solution would give the location of the receiving antenna when the recording was made and the displayed time would also correspond to when the signals were recorded and be off from the current time by a week. John WA4WDL -------------------------------------------------- From: "MailLists" <lists@medesign.ro> Sent: Thursday, April 12, 2012 1:33 PM To: "Discussion of precise time and frequency measurement" <time-nuts@febo.com> Subject: Re: [time-nuts] Re-radiating a GPS signal...?? > Purely geometrically, the fix solution is computed as the intersection > point of spheres with the radii determined by the propagation time,

Björn

Björn

It is well known that vertical accuracy is worse by about 1.8 times the horizontal accuracy. It is true this is geometrically caused. In indoor scenarios high sensitive receivers have a vertical bias due to excessive multipath. More or less all received signals have bounced multiple times to reach the receiver in the worst scenarios. This however has nothing to do with a rerad-system, where your rerad signal will be much stronger than the natural one. Otherwise there would be no need for a rerad-system in the first place. Also a correctly installed rerad-system will not give excessive multipath problems. Vertiacal biasing is not caused by (correctly) installed rerad systems. -- Björn > Purely geometrically, the fix solution is computed as the intersection > point of spheres with the radii determined by the propagation time, and > the centers by the positions of the satellites (practically not all > spheres intersect in the same geometrical point, so an average is > computed). > If the GPS Rx would receive simultaneously all satellites, considered > evenly distributed on a sphere, then the added path delays would mostly > cancel out - but if only the visible satellites are accounted for, we > will have an unbalanced system, approximated to an hemispehere, in which > the horizontal error will be low, as the longer paths cancel mostly out, > but for the vertical one it's not the case. > > Any GPS receiver will exhibit lower vertical precision than the > horizontal one. > The same phenomenon, of low precision, and biasing of position is > evident if just a part of the constellation is used (an obstacle > obscures a large part of the sky). > > The internal delays of the Rx are mostly fixed and known, so they can be > accounted for, and compensated in the firmware fix solution, but the > cable length is a variable (depending on the installation) factor, not > accounted for. > > > On 4/12/2012 7:15 PM, bg@lysator.liu.se wrote: >> Not at all! >> >> The (first) receiving antenna defines the position you get out of a long >> antenna cable or a reradiating system. The delays in LNA, filters, >> cables, >> rerad antenna, free air between rerad antenna and final receiving >> antenna >> ALL goed into the receiver clock error. This is clear both from a >> theoretical point, from most standard GPS texts and from practical >> experience from multiple installations I have used over the years. >> >> If you disagree, please provide evidence. >> >> -- >> >> Björn >> >>> Not quite, the delay of the antenna cable is affecting less the >>> horizontal position (it depends also on the current received >>> constellation geometry), but mostly the height ASL of the fix point, >>> prolonging simultaneously all the paths from the satellites with a >>> fixed >>> value. >>> Also, the propagation speed in a cable is significantly lower than in >>> free space - the perceived delay increase is ~1.5 times for usual >>> cables >>> (~.67 velocity factor), and the computed fix point would have a lower >>> height ASL than the real one. >>> >>> Those relaying systems are merely good for an approximate location fix, >>> mostly for not loosing the GPS signal in covered areas so that the >>> reacquire of the real signal is faster, with almost no perceived >>> discontinuity. >>> >>> >>> On 4/12/2012 6:11 PM, David McGaw wrote: >>>> The time/position fix would be from the location of the receiving >>>> antenna of the repeater, degraded only by noise. >>>> >>>> This should work if both antennas have good back-side rejection >>>> (choke-rings are particularly good for this but perhaps any good >>>> timing >>>> antenna could meet this), the re-transmitting antenna is close to >>>> being >>>> directly under the receiving antenna, and the system gain is low >>>> enough. >>>> The problem I would see in a room that is not fully shielded is >>>> interference between the direct and retransmitted signals at the >>>> receiver under test. >>>> >>>> David N1HAC >>>> >>>> On 4/12/12 10:17 AM, MailLists wrote: >>>>> GPS being extremely time-dependent, any delay introduced will affect >>>>> positioning precision. Also, the signal is too weak for such an >>>>> amplification/echo cancelling signal chain. >>>>> Passive relaying, or using at most a simple amplifier with low enough >>>>> gain, and short signal delay, remain the only feasible concepts. >>>>> >>>>> On 4/12/2012 4:48 PM, Azelio Boriani wrote: >>>>>> Passive UHF TV repeaters were in use in Italy too. Nowadays, for the >>>>>> DVB-T >>>>>> TV, active gap-fillers are used instead. Active gap-fillers are >>>>>> same-channel repeaters with the necessary, sophisticated echo >>>>>> suppression >>>>>> technique. We have developed our echo suppression signal processor >>>>>> on >>>>>> a >>>>>> Xilinx Virtex5 FPGA: maybe something similar may be done for the GPS >>>>>> CDMA. >>>>>> >>>>>> On Thu, Apr 12, 2012 at 3:29 PM, Alan >>>>>> Melia<alan.melia@btinternet.com>wrote: >>>>>> >>>>>>> If the isolation is good and the "clear view" signal is reasonably >>>>>>> strong, >>>>>>> the passive system works well in hangers, metalclad warehouses, >>>>>>> ferry lorry >>>>>>> decks. >>>>>>> The passive system in the UK used to be refered to as the "Matlock >>>>>>> Repeater". >>>>>>> >>>>>>> Alan >>>>>>> G3NYK >>>>>>> >>>>>>> ----- Original Message ----- >>>>>>> From: "Michael Baker"<mpb45@clanbaker.org> >>>>>>> To:<time-nuts@febo.com> >>>>>>> Sent: Thursday, April 12, 2012 2:05 PM >>>>>>> Subject: [time-nuts] Re-radiating a GPS signal...?? >>>>>>> >>>>>>> >>>>>>>> Time-nutters-- >>>>>>>> >>>>>>>> So-- How do GPS signal re-radiators work? >>>>>>>> >>>>>>>> How do you place a GPS antenna on top of a building, >>>>>>>> pick up the signal with an LNA, amplify it to re-transmit >>>>>>>> on an inside antenna without the amplified re-transmitted >>>>>>>> signal getting back into the roof-top receiving antenna? >>>>>>>> >>>>>>>> I can see circumstances where a huge metal building >>>>>>>> (aircraft hangar?) might provide enough isolation to >>>>>>>> prevent problems, but in many cases I wonder about it... >>>>>>>> ---------------------------- >>>>>>>> >>>>>>>> As an aside note-- I recall seeing, many years ago, a totally >>>>>>>> passive TV signal repeater on top of a tall hill in mountainous >>>>>>>> territory relaying a TV station signal to some homes in a valley >>>>>>>> just below. The passive repeater consisted of an array of >>>>>>>> high-gain UHF yagis pointing to the 40 mile distant TV station >>>>>>>> tower. >>>>>>>> The yagi array was coupled to another set of high-gain yagi >>>>>>>> antennas pointing down to the homesites in the valley. I was >>>>>>>> told that it worked pretty well. >>>>>>>> >>>>>>>> Mike Baker >>>>>>>> ---------------------- >>>>>>>> >>>>>>>> _______________________________________________ >>>>>>>> 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. >>> >>> _______________________________________________ >>> 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. >