Measuring Distance via Radio Waves
Measuring Distance via Radio Waves
(OP)
Does anyone know of a way to use radio to radio transmission to determine the distance between the two radios with an error of about a meter? These radios would need to be small and economical - preferably transmitting on a free frequency with the longest range possible.





RE: Measuring Distance via Radio Waves
TTFN
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RE: Measuring Distance via Radio Waves
Doing your own design may be interesting, and sounds like a schoolboy project. But it could be a legit hobby question.
IRStuff gave you the answer for a commercial quality product. You don't even have to put up your own satellite constellation.
RE: Measuring Distance via Radio Waves
Dan - Owner

http://www.Hi-TecDesigns.com
RE: Measuring Distance via Radio Waves
RE: Measuring Distance via Radio Waves
I'm unclear what you mean by "pricey." Do you really think that your custom design will be cheaper than a mass-produced GPS, particularly since you need as good as, if not better, timing performance, coupled with no simple means of synchronizing the time? Without something like a cell tower network, the amount of RF you need to generate will not be in the free regime. Without a GPS-like modulation scheme, you're going to get garbage for time synchronization in a typical city with tons of multipath.
You seem to be ignoring the overall problem of multipath and seem to think that this is a trivial problem. If it were that easy, GPS would have been supplanted by now. Have you even considered how accurate your timebases need to be?
I suggest that you look that one of the following as a more realistic alternative:
> GPS-equipped cell phones
> a cell carrier that will give you triangulated data from their cell towers for non-GPS cell phones
> Earthmate LT-20 only costs about $60. If wired to a simple USB-equipped microcontroller, you could do the hardware for less than $180 per installation.
TTFN
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RE: Measuring Distance via Radio Waves
Contact the telematics group at the major cell phone companies. They specialize in making just this sort of device for people like you. You are their target market. They take sensitivity and reliability seriously.
In your own design making ad-hoc networks is not trivial. Also if you have a unit that has visibility to only other units in a plane or even worse co-linear, then doing the math to get location has issues.
RE: Measuring Distance via Radio Waves
RE: Measuring Distance via Radio Waves
RE: Measuring Distance via Radio Waves
If you use pulses, that works but is often messy. This company in San Diego (forgot the name) would set up a CW, or nearly CW signal and change the phase of the signal on transmit, the receiver would pick it up and transmit on a different frequency the same received signal. They knew the inherent time delay thru the repeater and the original transmitter measures delay in the received phase shifted signal.
The primary reason this technique is good is that ground bounces don't change much in the time it takes for the energy to fly out and return back to you. (about 10.5 microseconds per mile distance between the two points).
I'm not sure if there are any transceiver modules readily available to use this technique, but maybe you can build your own hardware. Video and RF/IF bandwidth considerations will affect the actual rise time of the 180 phase shift and hence the distance measuring accuracy of the system. Not certain of the details.
kch
RE: Measuring Distance via Radio Waves
is by using a carrier modulated by a pseudo random sequence (which as VisiGoth points out results in a spread spectrum signal). Eg a 10 bit PRS at a 5MHz chip rate will do it provided you have a good correlator in the receiver.
The frequency must be UHF or higher to allow the bandwidth needed so range will be limited limited.
You'll need a good Kalman filter in each RX to eliminate the effects of multi-path and the variations in propogation delay you'll encounter.
Using DGPS is going to be a lot cheaper although even that will only give the position of each unit.
RE: Measuring Distance via Radio Waves
RE: Measuring Distance via Radio Waves
kch
RE: Measuring Distance via Radio Waves
RE: Measuring Distance via Radio Waves
RE: Measuring Distance via Radio Waves
ht
Standard Loran C accuracy was 460 m: http://www.navcen.uscg.gov/eLORAN/overview.htm
TTFN
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RE: Measuring Distance via Radio Waves
http://www.acam-usa.com/Content/English/acam.html