# [time-nuts] question for expert time guys

Stefan Heinzmann stefan_heinzmann at gmx.de
Fri Feb 1 09:23:04 EST 2013

Can the base stations be interconnected via cable?

In that case, wouldn't it suffice to have the mobile device send an
unmodulated carrier of low enough frequency, and compare the phase
between the receiving base stations, taking the (known) cable delays
into account?

Cheers
Stefan

Rick Harold wrote:
> To time experts/EE's.
>
> 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.
> These two type of devices (fixed and mobile) are all under my control and
> thus customized as needed.
>
> The mobile device (not a phone, custom device) would be the least expensive
> item.  I'd like a range of 150 feet or better and accuracy of 3 feet or
> better.
> When manufactured these items they can be calibrated in order to adjust for
> any variation in IC's, discrete components etc...
> We can assume for now the temperature is constant 70 degree temperature.
> Cost is the key design factor.
>
> The general flow is:
>
>     1. base station 1 indicates we are determining position of device A.
>     2. Each base station 1, 2, 3 take turns pinging the device to determine
> distance.
>     3. A ping consists of (something like, e.g. frequencies as examples)
>          -send 915mhz signal from base station to device
>          -device response ASAP on different frequency
>          -station waits and counts 'time' for return
>          -this is repeated N? times to get best avg/accuracy.
>          -The mobile device does not move very fast
>     4. Since delays of the process on each unit is calibrated the device and
> base station would subtrack that time out from the results.
>     5. obviously with 3 distances we can determine the 2D position of the
> mobile device
>
> I know the time accuracy is the key to count time =  feet, 1ns.  This
> overall project is not new concept.   How to make it "inexpensive" is key.
> how inexpensive, very ;-)   no OCXO or expensive components like that.
>
> That's my goal, and I'm looking for help on the design/thought process of
> getting there.
> I am open to a consulting arrangement for a fee, please email if you like.
>   I've worked with 'regular' EE's (I'm a software guy) but this time
> accuracy is too much for them.
> Esp. finding a way to do it inexpensively.
>
> Thanks for any thoughts.
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