# Distance measurement

Discussion in 'Electronic Design' started by GeoSound, Jun 12, 2008.

1. ### GeoSoundGuest

Trying to conger up a means to measure distance from a radio tower.
Thought that maybe one could capture the time of reception of the direct
wave then from a reflected wave at known distance from the antenna doing
the direct capture measure the difference (shift) to know the distance
from the tower. Without a unique signature, I am presuming that a
computer program could be written to find where the 2 signals should
have matched in order to find the difference. Is this a viable idea or
have I slipped over the edge or forgotten basic physics? Dale

2. ### PeterDGuest

I think you slipped over the edge!

I know you can measure the distance to the reflector that way, and I
supose if you know the distance to the reflector, and the distance
from the relector to the source you can then comput the final leg of
the triangle...

3. ### PeterDGuest

Actually if you know the location of the transmitter and the
destination, any good GIS software will tell you the straight line
distance.

4. ### mpmGuest

What exactly are you trying to do?
I am assuming you (the device?) is mobile, and you want to know how
far you (the device?) is from one or more particular towers.
Since "towers" are almost always stationary, if you (the device) are
also stationary, then some simple math will take care of the request.

For cell phones, many carriers use a technique called time difference
of arrival (TDOA).

You would have to do this in reverse, and it might not be possible
given the information you will likely have at your disposal.
You might be able to do something with Loran or GPS, etc...??

How much accuracy do you need? -mpm

5. ### Frank RaffaeliGuest

TDOA will show bearing to the propagated wave (direction), but not
distance.

Frank

6. ### JosephKKGuest

You have that backwards. It shows distance not direction. Phase
difference can be used for direction at those frequencies.

8. ### JosephKKGuest

Really? How/why does the time TDOA data result in hyperbolic curves?
As i said, TDOA does not give bearing, for two data values, but a
line/curve of delta distance. You correctly pointed out comparing
TDOA from three or more points can produce 2-d (or spherical)
location.
For any doublet of two transmitters - one receiver or vice versa, it
gives delta distance, not bearing.
I have no clue as to your age, but i am of quite an age. I have been
conversant with the theory and practice of Loran, DME, TACAN, VOR