Jeff wrote:

Your scheme is doomed to failure.

Although signal strength is proportional to disrtance it
is also affected to too many other things as well.

For your scheme to work both transmit and receive
antennas must be truly omni-directional with no
lumps in the polar diagram (not easy espicially
mobile). The terain must not cause any disturbance
to the signal (impossible). There should be no
reflections. The transmit power or receive gain
must not change. I am sure there are a few more
that I have not thought of off the top of my head.

Having said that such a scheme could give a very
approximate location if the data was analysed and
anomolous readings ignored.

Regards
Jeff

While it may be doomed to failure the value of the theory is sound and
it is one of the techniques that can be used to determine user location
of a cell phone except that the cell phone solution also have the time
similar to GPS so they can use time instead of field strength.

It is an interesting idea theoretically. You could plot circles on a map
from the relative signal strength value and centered on the GPS
location, then increase the circle sizes proportionally until they
intersect and this will provide a rough idea of the location. With more
locations it would be better and better, throwing out some of the
circles that don't fit. It will probably work if you live in one of the
plains states and have a very sensitive RF meter and lots of driving time.

Dale





--
_ _ Dale DePriest
/`) _ // http://users.cwnet.com/dalede
o/_/ (_(_X_(` For GPS and GPS/PDAs

Jeff wrote:

Your scheme is doomed to failure.

Although signal strength is proportional to disrtance it
is also affected to too many other things as well.

For your scheme to work both transmit and receive
antennas must be truly omni-directional with no
lumps in the polar diagram (not easy espicially
mobile). The terain must not cause any disturbance
to the signal (impossible). There should be no
reflections. The transmit power or receive gain
must not change. I am sure there are a few more
that I have not thought of off the top of my head.

Having said that such a scheme could give a very
approximate location if the data was analysed and
anomolous readings ignored.

Regards
Jeff

While it may be doomed to failure the value of the theory is sound and
it is one of the techniques that can be used to determine user location
of a cell phone except that the cell phone solution also have the time
similar to GPS so they can use time instead of field strength.

It is an interesting idea theoretically. You could plot circles on a map
from the relative signal strength value and centered on the GPS
location, then increase the circle sizes proportionally until they
intersect and this will provide a rough idea of the location. With more
locations it would be better and better, throwing out some of the
circles that don't fit. It will probably work if you live in one of the
plains states and have a very sensitive RF meter and lots of driving time.

Dale





--
_ _ Dale DePriest
/`) _ // http://users.cwnet.com/dalede
o/_/ (_(_X_(` For GPS and GPS/PDAs

Scott in Aztlan wrote:

Suppose you were participating in a search for a hidden radio transmitter, only
instead of the usual radio receiver with a directional antenna you have a
receiver with an omnidirectional antenna and a GPS receiver.

What is the reason for the constraint? I have used loops at frequencies
from a couple hundred Hertz up to 30MHz and I know they work even
higher. Why not use a loop?

There are a lot of factors besides distance affecting signal strength.
You would have to use an approximation to the inverse square law and
look at the area described by drawing circles from each reading. The
area common to all the circles would be your guess. You would then want
to get closer and repeat.

Ted

Scott in Aztlan wrote:

Suppose you were participating in a search for a hidden radio transmitter, only
instead of the usual radio receiver with a directional antenna you have a
receiver with an omnidirectional antenna and a GPS receiver.

What is the reason for the constraint? I have used loops at frequencies
from a couple hundred Hertz up to 30MHz and I know they work even
higher. Why not use a loop?

There are a lot of factors besides distance affecting signal strength.
You would have to use an approximation to the inverse square law and
look at the area described by drawing circles from each reading. The
area common to all the circles would be your guess. You would then want
to get closer and repeat.

Ted

Scott in Aztlan wrote:

On Sat, 13 Sep 2003 17:54:35 GMT, Ted Edwards wrote:

Suppose you were participating in a search for a hidden radio transmitter, only
instead of the usual radio receiver with a directional antenna you have a
receiver with an omnidirectional antenna and a GPS receiver.

What is the reason for the constraint?

The radio receiver in question has a built-in omnidirectional antenna and no
jack for an external antenna.

What frequency?

Ted

Scott in Aztlan wrote:

On Sat, 13 Sep 2003 17:54:35 GMT, Ted Edwards wrote:

Suppose you were participating in a search for a hidden radio transmitter, only
instead of the usual radio receiver with a directional antenna you have a
receiver with an omnidirectional antenna and a GPS receiver.

What is the reason for the constraint?

The radio receiver in question has a built-in omnidirectional antenna and no
jack for an external antenna.

What frequency?

Ted

You could still make a directional bias with a reflector of some sort.

Scott in Aztlan wrote:

On Sat, 13 Sep 2003 17:54:35 GMT, Ted Edwards wrote:

Suppose you were participating in a search for a hidden radio transmitter, only
instead of the usual radio receiver with a directional antenna you have a
receiver with an omnidirectional antenna and a GPS receiver.

What is the reason for the constraint?

The radio receiver in question has a built-in omnidirectional antenna and no
jack for an external antenna.

--
Friends don't let friends shop at Best Buy.

You could still make a directional bias with a reflector of some sort.

Scott in Aztlan wrote:

On Sat, 13 Sep 2003 17:54:35 GMT, Ted Edwards wrote:

Suppose you were participating in a search for a hidden radio transmitter, only
instead of the usual radio receiver with a directional antenna you have a
receiver with an omnidirectional antenna and a GPS receiver.

What is the reason for the constraint?

The radio receiver in question has a built-in omnidirectional antenna and no
jack for an external antenna.

--
Friends don't let friends shop at Best Buy.

Ted Edwards writes:

*snip*

Perhaps if you were on a flat open surface, you could plot location
and signal strength from many data points, and extrapolate the centerpoint.
However considering uneven terrain and trees, buildings, etc
your uncertainties would become large. Unless you had perfect
knowledge of the surroundings and reflections it becomes
not impossible perhaps but very very difficult. Wonder why you
would deliberately try to swim in a straitjacket.

Directional antennas exist. Time is money, instead of
taking many time-consuming readings for hours and solving
a complex problem.....



--
Vincent Fox
Georgia Institute of Technology, Atlanta Georgia, 30332
uucp: ...!{decvax,hplabs,ncar,purdue,rutgers}!gatech!pri sm!vf5
Internet:

Ted Edwards writes:

*snip*

Perhaps if you were on a flat open surface, you could plot location
and signal strength from many data points, and extrapolate the centerpoint.
However considering uneven terrain and trees, buildings, etc
your uncertainties would become large. Unless you had perfect
knowledge of the surroundings and reflections it becomes
not impossible perhaps but very very difficult. Wonder why you
would deliberately try to swim in a straitjacket.

Directional antennas exist. Time is money, instead of
taking many time-consuming readings for hours and solving
a complex problem.....



--
Vincent Fox
Georgia Institute of Technology, Atlanta Georgia, 30332
uucp: ...!{decvax,hplabs,ncar,purdue,rutgers}!gatech!pri sm!vf5
Internet: