Distance measurement

[GeoSound]

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

 

[PeterD]

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

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...

 

[PeterD]

Portable GPS might be easier. Accuracy is very good these days and the
units are affordable and useful for other things.

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

 

[mpm]

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

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).
Do a Google search.

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

 

[Frank Raffaeli]

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).
Do a Google search.

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

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

Frank

 

[JosephKK]

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

Frank

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

 

[JosephKK]

In fact, both Frank and Joseph have it wrong. Flight-time differences
taken using two receivers and one transmitter (or two transmitters and
one receiver) give you a solution that places the unknown unit
somewhere on a hyperbolic curve. Both direction and distance are
ambiguous until you add a third receiver (or transmitter), which
allows you to draw two more curves. The unit you're trying to locate
then lies at the intersection of those curves, giving both direction
and distance.



http://en.wikipedia.org/wiki/LORAN

(Interferometry, which is what Joseph is alluding to, is the limiting
case of this, where the transmitter is very far from the two receivers.
All of the ambiguity is in distance, and the direction is known.)

Attempting to do this with a single tower along with some sort of
multipath (passive reflections) would require that you know exactly
where the reflector(s) are and that they are in fact the reflections
being used for all positions of the unknown unit. In fact, you would
need to place directional antennas on the tower that point at the
reflectors you want to use, with each one going to its own receiver
so that you know which signal is which.

If all you really want is distance, and the mobile unit can participate
actively -- i.e., carry a transponder -- you might want to consider the
technique used for aircraft "DME" (distance measuring equipment).

http://en.wikipedia.org/wiki/Distance_measuring_equipment

-- Dave Tweed

 

[JosephKK]

In fact, both Frank and Joseph have it wrong. Flight-time differences
taken using two receivers and one transmitter (or two transmitters and
one receiver) give you a solution that places the unknown unit
somewhere on a hyperbolic curve. Both direction and distance are
ambiguous until you add a third receiver (or transmitter), which
allows you to draw two more curves. The unit you're trying to locate
then lies at the intersection of those curves, giving both direction
and distance.

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.

http://en.wikipedia.org/wiki/LORAN

(Interferometry, which is what Joseph is alluding to, is the limiting
case of this, where the transmitter is very far from the two receivers.
All of the ambiguity is in distance, and the direction is known.)

For any doublet of two transmitters - one receiver or vice versa, it
gives delta distance, not bearing.

Attempting to do this with a single tower along with some sort of
multipath (passive reflections) would require that you know exactly
where the reflector(s) are and that they are in fact the reflections
being used for all positions of the unknown unit. In fact, you would
need to place directional antennas on the tower that point at the
reflectors you want to use, with each one going to its own receiver
so that you know which signal is which.

If all you really want is distance, and the mobile unit can participate
actively -- i.e., carry a transponder -- you might want to consider the
technique used for aircraft "DME" (distance measuring equipment).

http://en.wikipedia.org/wiki/Distance_measuring_equipment

-- Dave Tweed

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
VORTAC, IFF, 2-d and 3d radar, and sonar for decades. Please do not
be too dismissive of me. I might consider it impolite.

 

[JosephKK]

What shape do you think the curve has? If you are indeed "conversant"
with these systems, you should know this, especially given the Wikipedia
reference I gave to refresh your memory.


Was I being dismissive?

I considered it a possibility.

I was just trying to help the OP understand his options, using your
message as a springboard for my own additional comments. Age is not
the issue here; accurate and useful information is.

-- Dave Tweed

Dead on. Did not mean to be sloppy though. But may have went
overboard in oversimplifying for OP.