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wireless signal generation device

J

Jon Slaughter

Jan 1, 1970
0
I'm thinking about starting a project which is essentially based on
determining distances(and derivations from that) using triangulation on to
fixed and one variable source. I would put a signal generator on the
variable source and determine its distance using triangulation by
calculating the time it takes for the signal to arrive at the fixed
locations and once I know the distances I can recover the speed and do all
the things that makes the project interesting.

I assume the method I'm using is pretty much the standard in doing this
sorta thing. The issue I'm having is that I do not know anything practical
about it. Before I even think about starting this project I need to know
how hard it would be to create(or buy) a device that emits a signal that the
other two devices can use to determine the distances.

Here are some specs: The distances used are at most a mile but in actuality
will probably be a few hundred meters. The devices will be used
intermittently with about 1-4 mins continuous use. It needs to be as
accurate as possible but not excessively so(I'd like to get millimeter
resoluion but centimeter's would be ok or maybe even inches). The device
needs to be as small as possible except for the antenna which could be
several inches as long as it is not to large and does not weigh to much.
Ofcourse cost is a factor but for such a simple device I would imagine the
main factors involved in cost are minaturization. The device would need to
emit a signal between 10 and 1000hz but I believe that it would need to
actually work in a much higher frequency range(ghz) to be practical.

I think thats about the main things. The other parts of the project mainly
have similar limitations except size is not as a huge issue.


Basically what I want is something like the transmitter of a cell phone that
sends a periodic wave of a few hz that can be picked up about 500-1000
meters away by a device which can then use it to determine the distance of
that device away from the reciever. Ofcourse I'll have two of these devices
and they will do the same with each other to get the position(2D as I know
altitude of the transmitter).

Ofcourse using this method will require that the speed of the
electromagnetic wave be constant or approximately. There will be direct line
of sight from all the devices except for possible momentary
interruptions(sign in the way, etc...).


Just looking for some feedback. Hopefully I gave all the necessary
information.

Thanks,
Jon
 
B

Bob

Jan 1, 1970
0
Jon said:
I'm thinking about starting a project which is essentially based on
determining distances(and derivations from that) using triangulation on to
fixed and one variable source. I would put a signal generator on the
variable source and determine its distance using triangulation by
calculating the time it takes for the signal to arrive at the fixed
locations and once I know the distances I can recover the speed and do all
the things that makes the project interesting.

I assume the method I'm using is pretty much the standard in doing this
sorta thing. The issue I'm having is that I do not know anything practical
about it. Before I even think about starting this project I need to know
how hard it would be to create(or buy) a device that emits a signal that the
other two devices can use to determine the distances.

Here are some specs: The distances used are at most a mile but in actuality
will probably be a few hundred meters. The devices will be used
intermittently with about 1-4 mins continuous use. It needs to be as
accurate as possible but not excessively so(I'd like to get millimeter
resoluion but centimeter's would be ok or maybe even inches). The device
needs to be as small as possible except for the antenna which could be
several inches as long as it is not to large and does not weigh to much.
Ofcourse cost is a factor but for such a simple device I would imagine the
main factors involved in cost are minaturization. The device would need to
emit a signal between 10 and 1000hz but I believe that it would need to
actually work in a much higher frequency range(ghz) to be practical.

I think thats about the main things. The other parts of the project mainly
have similar limitations except size is not as a huge issue.


Basically what I want is something like the transmitter of a cell phone that
sends a periodic wave of a few hz that can be picked up about 500-1000
meters away by a device which can then use it to determine the distance of
that device away from the reciever. Ofcourse I'll have two of these devices
and they will do the same with each other to get the position(2D as I know
altitude of the transmitter).

Ofcourse using this method will require that the speed of the
electromagnetic wave be constant or approximately. There will be direct line
of sight from all the devices except for possible momentary
interruptions(sign in the way, etc...).

since nobody else has replied I mention a few reasons
measuring distance in this way with useful accuracy
will be troublesome.

Plextek have done something vaguely similar with 10meter range.
http://www.plextek.co.uk/brochure/lost-it.pdf

An antenna a few inches long will only work efficiently
at UHF frequencys but for a few hundred meters range you
can communicate with a short antenna on a portable device
and larger antennas on the fixed equipment.

13.56Mhz is probably most suitable for this.
VHF/UHF signals tend to bounce off the ground,
buildings etc giving multipath reception.

Measuring the absolute time a transmission takes to
arrive is not practical with one transmitter and one receiver.
You could have a clock at both points and send a transmission
exactly once every ten seconds. The speed of light is
approximately one nanosecond per foot so you need atomic clocks
to get worthwhile accuracy.

Perhaps a scheme where one end receives the signal and
retransmits its back on another frequency could be made to
work. Transmitting and receiving at the same time requires
some careful RF engineering.
GSM mobile phones compensate for the speed of light
using a "timing advance" value in 350meter steps.

A simple scheme using presence or absence of an RF carrier
will have trouble detecting exactly when a transmission
starts.
When the signal is limited to a narrow frequency band
the signal does not go from nothing to full strength at
the detector/demodulator instantly, it rises out of the
noise over quite a few cycles. It's hard to tell if the
start is the real start or some noise that looks like the
start. Also the local noise levels at the receivers will vary.

A scheme using an audio frequency signal
modulated onto the audio might work or might have enough
jitter to make timing measurements useless.
A microsecond variation gives you a 1000 foot error.

If you try to use microwave frequencys with 100+MHz
bandwidth you have a lot of thermal noise and other
noise to contend with. More bandwidth means more noise.

Bob
 
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