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.
