using RF to measure distance 1

[shamone]

Hi, I am trying to measure the distance between a stationary point and a moving point up to at most 1200ft. I think RF is the best(or only way) to do it. Wondering if anybody knows an effective, cost efficient, method of doing this. The distance is not always line of sight either. Thanks.

 

[IRstuff]

What is the intent? RF needs line of sight as well. Otherwise, you're not getting lineal distance.

Why not use DGPS?

TTFN

 

[shamone]

Ok lets make it so that it is always line of sight. I wanna us RF as a cheaper alternative to GPS.

 

[IRstuff]

By continually failing to provide adequate information, how do you expect to get a serious answer?

what accuracy?
how much money?

TTFN

 

[shamone]

I am looking for an accuracy of around +/- 5 feet or better. Price wise of course as cheap as possible but lets say around $100. This is just a guess for price. I am trying to see if its feasable to do. ANy more info? That should be enough

 

[IRstuff]

Just one?
NRE?
temperature range?
environment?


TTFN

 

[shamone]

It is going to be used in a flat feilds with tree surroundings. Going to used on normal outside temps no less than 0 degrees C. There are going to be more than one used within a close proximity(lets say around a 50 to 200 feet from eachother). Not sure what NRE is. Sorry, i am new at this. Thanks for you patience.

 

[richs]

Think radar gun-

You can hack one up to use non-doppler ranging.


Best of luck and have fun.

Cheers,

Rich S.

 

[shamone]

i was considering using radar but worried about hitting the wrong point but i will look into it some more. Thanks

 

[MikeHalloran]

You could send out a radio burst and an audio burst at the same time, measure the time between receipt of each, and use the speed of sound to infer the distance. Better to measure the temperature also, and compensate for that. The audio could be ultrasonic, but it will need some power, and you'll have to characterize the response time of the receiver, e.g. how many cycles it needs to reliably distinguish a burst from random noise.

If the moble unit can measure the distance traveled and its compass heading, it could infer its position by dead reckoning.

If you could arrange two stationary sources of bright light or continuous RF, the mobile unit could use a rotating directional receiver to measure the bearing to each source and infer its position.

Absent interfering trees, bushes, people, etc., you could just keep a string taut between the units, and measure the extension of the string.






Mike Halloran
NOT speaking for
DeAngelo Marine Exhaust Inc.
Ft. Lauderdale, FL, USA

 

[IRstuff]

Radar on a non-Doppler basis could be difficult.

A 35-GHz radar with a 6-inch antenna will have a beam width of about 8 degrees. At 1200 ft, the beam footprint would be about 165 ft across. Without Doppler, there would be no target discrimination.

Bushnell has a number of laser rangefinders that sell for less than $200:

http://www.nextag.com/All--PRICE-Under-200--zzbushnell+laser+rangefinderz1zB3mz5---html

and without beam size issues.

TTFN

 

[walker1]

We bought a range finder off the shelf from a hunting supply shop the other year. Binocular look-alike.

It uses a IR laser diode and works well at ranges beyond your needs. (has been tested at 1500 feet or so)
As this is Europe, the range comes in meters, though

 

[zeusfaber]

Add to your list of options secondary radar (interrogator/receiver at one end and transponder at the other).

Strongly suspect that you'll find the laser rangefinder is a better solution, but if you're expected to do a feasibility study, it would be nice to offer alternatives that work.

A.

 

[shamone]

Thanks for all the input guys. I am a recent grad so it is nice to hear some advice from some pros. I am trying to keep the price as minimal as possible. I am also interating it with a microprocessor and an LCD display for my own specialty functions. I think the Rf seems to be the best way to go. Keep the feedback coming as it is very helpful.

Cheers,

mark

 

[VEBill]

Use two transceivers (probably UHF) that ping back and forth with as little latency as possible. By measuring the overall cycle time you should be able to get a relationship between cycle period and distance. There will likely be an offset due to the zero-distance minimum cycle time, and this offset might vary with environmental factors.

The cycle time is obviously going to be in the RF range, so you're going to have to use very fast hardware to count it. The system will have a minimum distance increment probably in the several meter (or tens of meters) range.

Or just use DGPS.

 

[itsmoked]

Nice, clean, to the point, I like it VE1BLL.

 

[shamone]

Thanx VE1BLL, I had your idea in my head to begin with, it seems to be the most appropriate way to do it. One question about actually calculating the distance. Do I use the general (speed of light)*time?

Cheers

 

[Warpspeed]

With any radio system there is always going to be the possibility of multi path reception. The receiver may possibly detect several signals all slightly displaced in time. The most direct and shortest signal may not always be the strongest either. Spurious reflections from buildings and vehicles may be a problem with any simple radio system.

GPS combined with some sort of data link may still be the most reliable way to do it.

 

[IRstuff]

I had considered suggesting RF modems, but the synchronization is non-trivial, particularly when you consider that a 5-ft error is incurred with a 10-ns timing error

TTFN

 

[shamone]

there is gonna be no problems with cars and buildings interfering. It will not be used in that environment and it will always be line of sight. I will aslo gave each carrier a specific "identity" so it doesn;t mistakingly pick up other signals.