That's basically how GPS works, except that you need more than one
transmitter, or veddy expensive clocks in the receiver. Basically with GPS
you receive accurate time signals from four satallites. Since your receiver
doesn't know the time or it's position you have four equations (from four
satellites) in four unknowns and voila! you have an answer. You can do
differential GPS down to millimeter accuracy if you sense the phase of the
carrier.

Loran uses the same basic concepts (synchronized transmitters, speed of
light, yadda yadda), but it asks you to sense the phase difference between a
master and a slave TX, and it isn't nearly so accurate.

"Christopher" wrote in message
...
Hi guys,

ok, I've got an idea but it's based on determining the distance of a
transmitter from a receiver, I originally thought about a synchronised
clock in both units, the transmitter sends the time it has out, by the
time the receiver unit gets this time a period has passed (probably a
few millionth's of a second) and a diff time is detemined, combined with
the speed those waves travel, will reveal the distance.

however, physics decided this idea wouldnt work, since all
electromagnetic radiation travels at the speed of light, apparently,
DAMN, back to the drawing board.

I'm here to see if anyone has any way they can determine the distance
from transmitter to receiver, this isnt a great distance either and it
needs to be fairly, accurate, if it's not possible, it's not possible, I
just wanted to ask people far cleverer than i.

signal strength perhaps?

literally I am talking about a transmitter within a cuboid shaped
enclosure around 10m maximum and being able to pinpoint that transmitter
within that enclosure accurately, to around 1cm, perhaps 2cm.

like I said, if it's not possible, well then hey, thanks anyway, but
perhaps it is and therefore perhaps my idea will still be workable.

thanks guys! I'll be waiting for your answers or solutions

kosh

On Mon, 26 Jan 2004 16:55:44 -0800, "Tim Wescott"
wrote:

That's basically how GPS works, except that you need more than one
transmitter, or veddy expensive clocks in the receiver. Basically with GPS
you receive accurate time signals from four satallites. Since your receiver
doesn't know the time or it's position you have four equations (from four
satellites) in four unknowns and voila! you have an answer. You can do
differential GPS down to millimeter accuracy if you sense the phase of the
carrier.

Since the measurement should be done in a confined space, why not
switch the roles and use one transmitter on the moving object and four
receivers on known fixed locations around the perimeter of that space?

With the receivers connected by cables receiving a common clock
signal, the accuracy of the clock is not important, contrary to the
situation in GPS, in which the four satellites must have atomic clocks
to have a common time base.

Loran uses the same basic concepts (synchronized transmitters, speed of
light, yadda yadda), but it asks you to sense the phase difference between a
master and a slave TX, and it isn't nearly so accurate.

Space probe ranging is done by sending a high data rate pseudo noise
sequence from earth to the probe, in which a simple frequency
translation is done with a high accuracy local oscillator to a
different frequency and sent back to earth. From this, the total
earth-probe-earth phase difference of the PRN sequence (and possibly
also the total RF phase difference) can be determined and hence also
the distance.

However, in this case the accuracy requirement was 1 cm, so I guess
that at least 10 GHz (3 cm) radiation should be used.

Paul

You don't necessesarily need to have a carrier wavelength smaller than the
distance you want to measure, as long as you can accurately measure phase.
Assuming that you could measure phase to 10 degrees, for instance, a 1cm
accuracy would only require 900MHz (33cm).

Surveyor-quality differential GPS uses the 2.4GHz GPS carrier and measures
the differences in the carrier phase (not the phase of the pseudo-random
sequence) to get sub-cm accuracies.

"Paul Keinanen" wrote in message
...
On Mon, 26 Jan 2004 16:55:44 -0800, "Tim Wescott"
wrote:

-- snip --

However, in this case the accuracy requirement was 1 cm, so I guess
that at least 10 GHz (3 cm) radiation should be used.

Paul