Help in measuring distance between two points with RF

Discussion in 'Wireless & RF Design' started by fotondiamond, Oct 4, 2006.

  1. fotondiamond

    Thread Starter New Member

    Sep 14, 2006
    5
    0
    I need a measuring circuit to measure 2 points distance Via RF,
    has anybody a ready circuit?
     
  2. Papabravo

    Expert

    Feb 24, 2006
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    I don't think this can be done cheaply or easily, but what kind of distance range are you talking about? How many trnasmitters and receivers are we talking about.

    If the distances are on the order of tens of feet I think you will have big trouble resolving the difference between say 10 feet and 12 feet. If the distances are large then I doubt you will be able to achieve the power levels or construct the antennas required for such a feat.

    Having said all that, it is also possible that I could be wrong.
     
  3. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    Hi,

    If it is a long distance, look up radar circuits. If short, the way to go is ultrasonic sound.
     
  4. fotondiamond

    Thread Starter New Member

    Sep 14, 2006
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    0
    I want to measure 2 points distnace up to 1 km , and show it on LCD, my 2 points can not see together directly , sometimes some barriers are between them, then I think that ultrasonic is not suitable.
     
  5. Papabravo

    Expert

    Feb 24, 2006
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    I think there is no chance of using RF to measure distance if there are barriers between the transceivers.
     
  6. fotondiamond

    Thread Starter New Member

    Sep 14, 2006
    5
    0
    If RF is not suitable , what is your best suggest for me?
    Is it possible for you to inform me a ready circuit or extra resources or similar done applications?
     
  7. n9352527

    AAC Fanatic!

    Oct 14, 2005
    1,198
    4
    You could use a GPS receiver, moving from one point to another and calculate the distance. Or if you need simultaneous measurement, two GPS receivers with two persons communicating with short range radios or automatically by using GPS receivers with serial port and connecting them with short range radios (you need to built the comm link and processing circuit).

    The accuracy would be around 13-60 feet for each standard receiver, depending on where you live you could get one with WAAS or EGNOS capabilities and improve the accuracy to about 3-10 feet each.

    Not a cheap solution, but pretty much fool proof everywhere you go.
     
  8. Papabravo

    Expert

    Feb 24, 2006
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    GPS enabled cellphones that can SMS each other and have a serial port you can use to access the incoming SMS text messages. Check out Siemens XT56
     
  9. fotondiamond

    Thread Starter New Member

    Sep 14, 2006
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    I can not use GPS because:
    1- The 2 points are under ground 30 meter.
    2- Using GPS in our country is hard.

    Can I use RF in this Case:
    I send RF signal from A to B and start a timer, when B recieve this signal it sends an acknowledgement signal to A. When A recieve acknowledgement signal stop timer and calculate the distance.
     
  10. Papabravo

    Expert

    Feb 24, 2006
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    How much time does it take for light to go 1 km and return? Can you measure this interval with sufficient accuracy? I think not.

    How much delay would you expect there to be to receive and decode an incoming signal and generate a response? It will be many times the length of time for the signal to propagate.

    I understand your need for a solution but I don't think there is one, at least not an RF one. Sorry.
     
  11. sci-3d

    Well-Known Member

    Aug 22, 2006
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    I bough 8-100 cm Distance Sensor with $15. If 1 km, it would be not simple project and hight expense.
     
  12. EEMajor

    Well-Known Member

    Aug 9, 2006
    67
    4
    Another problem you would face is in the fact that you are measuring underground. Waves, both mechanical and electromagnetic, travel at different velocities in different mediums. In addition to having to be very, very, acurate in your measurements of how long the RF takes to make a round trip, you would have to factor in a slight difference in speed in the different densities of the material you are going through. Normally I wouldn't worry about this difference, because it is so small, but since you are using the velocity of an RF wave to calculate the distance, the density of the medium may become a large enough factor to worry about.

    Overall, I have to agree with Papabravo, there does not seem to be a very cheap, easy home-made solution to this problem. You may wish to contact a survey company and see if they have any solution for you. However, anything they have would be very expensive.
     
  13. EEMajor

    Well-Known Member

    Aug 9, 2006
    67
    4
    Oh, one more thing: Depending on your country, you will have issues with licensing RF transmitters unless they are very low power, (which would be too low to use underground). Again, your country's laws may be different, but in the USA, you would need a license, except in very few cases.
     
  14. vinay.pal2005@gmail.com

    New Member

    Jun 12, 2008
    1
    0
    Hi,

    As per my understanding of your requirement, i can suggest you one solution:

    You can use RF. use one RF transmitter receiver.

    Use a programmable variable resistor at receiving end.Now transmit the signal with different power level using Programmable resistor. and measure at reciever with same programed resistor value through your software.
    You have to make a look up table for different resistance value for distance.
    The size of lookup table will definitely depend on the distance to be measured and accuracy in distance.

    And the measured value of distance can easily be shown on any LCD.

    For further information you can mail me at

    vinay.pal2005@gmail.com
     
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