thaught i had for a similar system is to have one fixed transmitter broadcasting a signal to the thing you want to measure and also to all your measuring stations. the thing you want to measure would use that base frequency to crontroll its onboard oscilator and it would transmit its own signal on a different frequency. the measurment stations do the same conversion then compare the output of their modification to the origional signal with the signal they recieve with a phase comparitor. as the target moves you will be able to count wavelengths at each of your measurment points. you can also measure the output of the phase comparitor in analog if you want greater precision of measurement. difficulty you get is if the object moves quickly you could miss counts and loose the position of the object. -----Original Message----- From: pic microcontroller discussion list [mailto:PICLIST@MITVMA.MIT.EDU]On Behalf Of Marcel van Lieshout Sent: Friday, March 26, 2004 10:45 AM To: PICLIST@MITVMA.MIT.EDU Subject: Re: [EE:] Fastest logic family I believed my question was detailed enough, but I now do agree with you. I am trying to figure out if it is feasible to design a local positioning system (3D). Because I cannot set/measure the clock on the transmitter, I thought I best use the TDOA principle. I would therefore like to measure time of flight differences with an accuracy of as little mm as possible (max 10 mm). The RF frequency is 2.4 Ghz The maximum distance is 50 mtrs. A single transmitter at a time is active At least four receivers are present RealTime results are needed Several thousand (2500) measurements per second are needed. The acual location calculations are no problem, just a metter of enough cpu-cycles ;-) As I am basically a software-guy, I am not sure what information is relevant. Please, keep asking. Thank you for thinking with me! Marcel Robert Rolf wrote: > Over what distance range? At what carrier frequency? > Phase difference measurement can get you there as can various forms of > interferometry if the signal is CW. > > Look at how geodetic GPS can get down to mm with relatively cheap silicon. > > Does the result have to be supplied in real time? > > The CORRECT way to access the list's knowledge is to pose > the full problem so that our replies fit your constraints. > > Robert > > Marcel van Lieshout wrote: >> I'm trying to measures RF time-of-flight up to a few mm accuracy ( 10mm would be fine, 1 mm >> would be fantastic). Well, because I have no influence on the transmitter, I actually want to >> measure Time-Differences-Of-Arrival at several receivers. >> >> What do you (or anybody else) think? >> >> Marcel >> >> Jinx wrote: >>>> Hmm, not fast enough. Looking for something in the low picoseconds >>>> switching times :-0 >>> >>> ECL 100K is probably the fastest readily-available family, and 25GHz >>> (40ps) operation is the exception rather than the norm >>> >>> Googling around, it appears anything over that is very specialised, not >>> what you'd call a "family". Logic at up to 350GHz (2.8ps) appears to be >>> possible but in the experimental domain >>> >>> ;-) >>> >>> Do you actually need ps speed, or is there a way that what you're trying >>> do can be done by inference ? For example, in the way that high speed >>> oscilloscopes sample to build a waveform ? Can you improve what you >>> have or can get with liquid nitrogen for example ? >>> >>> -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email listserv@mitvma.mit.edu with SET PICList DIGEST in the body -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email listserv@mitvma.mit.edu with SET PICList DIGEST in the body