Determining distance and direction of known frequency transmitter.

Discussion in 'Wireless & RF Design' started by kyclopas, Jul 10, 2012.

  1. kyclopas

    Thread Starter New Member

    Jul 10, 2012
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    Is this a tall order?

    The transmitter and receiver communicate on the same frequency. The devices are portable but the measurements are taken when stationary. Range can be up to 150 meters from each other. Possible obstacles (ceilings/walls). Must be as portable as possible (smart phone size or smaller). Low power / but will only be on on demand by user.

    I would like to measure the distance and direction/angle to the transmitter as accurately as possible.

    What is a good frequency bandwidth for this?

    Is there a transmitter/receiver/antenna combination that can be used to provide info that an MCU can use effectively for calculation and display?

    Thanks
     
  2. WBahn

    Moderator

    Mar 31, 2012
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    What is "as accurately as possible" mean? To within ten meters? To within a meter? To within a centimeter?

    It's not trivial. You can use a directional antenna (or a phased array antenna) to determine direction pretty well, but it will be very possible that the signal from a reflection might be stronger than the signal from direct signal, especially if it is being partially blocked by an obstacle.

    Determining distance is a lot tricker. Using received signal strength is all but worthless. If you can get direction measurements from antennas located even a relatively small distance from each other, then you can triangulate a distance.

    Other options are available if you have a transceiver at both ends.
     
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  3. kyclopas

    Thread Starter New Member

    Jul 10, 2012
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    As accurate as possible would be about a meter. In fact this is a two way application so both ends are transceivers.

    What are the other options?
     
  4. WBahn

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    Mar 31, 2012
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    With a two-way system, you can do ranging by sending a query to the other station to which it replies with a fixed latency. The first station then uses the delay between the request and the reply to calculate straightline distance. For 1m accuracy, this will be challenging. Another way is to transmit a ranging tone one frequency and the other station then transmits the same tone at a different frequency locked to the tone it is receiving. The first station then looks at the phase offset of the two tones to compute distance.
     
  5. KL7AJ

    AAC Fanatic!

    Nov 4, 2008
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    The only reliable way of determining the distance to an unknown transmitter is by triangulation.

    If the ERP of the transmitting station is PRECISELY known (a VERY tall order just in itself), you can typically use field strength to obtain the distance with about a +/- 50% error.

    Eric
     
  6. WBahn

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    Mar 31, 2012
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    And the reliability of triangulation is amazingly poor in many real world situations. If you can have multipath reflections combined with ballistic path obstructions, then anything can happen. I remember an missing aircraft search I was on where the aircraft went down in eastern Colorado yet even when we were within a mile of the crash site the signals were unmistakeably coming from Pikes Peak. Aircraft flying near Pikes Peak though the same thing except for a tiny corridor that pointed to eastern Colorado. It took aircraft and ground teams all day to stay on the beam well enough to walk into the crash site.
     
  7. KL7AJ

    AAC Fanatic!

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    Just try triangulating on ionospherically reflected signals for a real challenge! This was a large part of my task at HIPAS observatory for performing ionospheric heating experiments. It CAN be done..but it takes a LOT of work!

    Eric
     
  8. WBahn

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    Mar 31, 2012
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    I'll bet!

    So what was the point/goal and what was the basic measurement technique (conceptually)?
     
  9. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    Actually it can be done using time of flight if both devices are transcievers, and "ping" back and forth to get accumulated TOF data. I believe some of the cellphone towers use their timers and a type of TOF system to determine an approx fix for the digital cellphone location. Since the OP only mentioned a transmitter and receiver this is probably not that relevant.

    As for a directional antenna that fits inside a smartphone size, I can't see that it would be very directional.

    People see this stuff in movies and think they can get a little button sized transmitter and stick it on someone, and use a 'phone sized device with a little screen that shows the exact location and distance of the target, and probably shows all the rooms of the building they are in too. ;)
     
  10. KL7AJ

    AAC Fanatic!

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    We used large arrays of circularly polarized antennas and measured the relative phasing. Took some serious MATLAB number crunching. :) I talk a bit about this in Radio Science for the Radio Amateur, to be published by ARRL early next year. Stay tuned!

    Eric
     
  11. aprillove1719

    New Member

    Jul 17, 2012
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    Transmitter hunting (also known as T-hunting, fox hunting, bunny hunting, and bunny chasing), is an activity wherein participants use radio direction finding techniques to locate one or more radio transmitters hidden within a designated search area. This activity is most popular among amateur radio enthusiasts, and one organized sport variation is known as amateur radio direction finding.
    Transmitter hunting is pursued in several different popular formats. Many transmitter hunts are organized by local radio clubs, and may be conducted in conjunction with other events, such as a radio enthusiast convention or club meeting. Before each hunt, participants are informed of the frequency or frequencies on which the transmitters will be operating, and a set of boundaries that define a search area in which the transmitters will be located. :)
     
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