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 <li...@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, b...@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.me...@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"<mp...@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. > _______________________________________________ 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.