[time-nuts] question for expert time guys

[Oz-in-DFW]

On 2/1/2013 3:45 AM, Hal Murray wrote:
> rickharold at gmail.com said:
>> I would like to triangulate a position of a device which moves using 3 fixed
>> positions devices of known location. The idea is to have these operate on
>> 915mhz or 434mhz or 2.4ghz or appropriate frequency. 
>> I'd like a range of 150 feet or better and accuracy of 3 feet or better. 
Doing this on radio will be tough.  You are likely to need on the order
of 10 or 20  MHz of ranging bandwidth to get the accuracy you want. 
This is also overkill in the extreme. 

For this range an line of sight I'd do it acoustically. Get some
piezoceramic transducers and do it at 40 KHz or so.  Transducers are ~$6
in single quantities.
http://www.mouser.com/ds/2/209/KT-400482-193462.pdf  Time of flight is
about 13.5 inches per *milli* second, so your microprocessor will have
time to do it's nails after processing ranging data.  You should also
get good accuracy and resolution. In general you shouldn't need to if
you are using active transmitters at both ends, but if you are worried
about multipath reflection use a PN code and use the first correlation
peak. 

Rich

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