Want to measure the distance between two objects using RF wave

Dear All,

I want to measure the distance between two objects. One is Wireless Transmitter (1st Object) and the other is Wireless Receiver (2nd Object). In between two objects, there can be many (hard) objects. But, I have to measure only the distance between Wireless Transmitter (1st Object) and Wireless Receiver. Is that possible?

help will be highly appreciated.

thanks

The problem is not adequately specified. There can be two possible answers:

Yes. If you calibrate the transmitter output power, antenna(s) gain and if you can measure receiver output power response to the power received from antenna, and if there is a free space between the transmitting and receiving antenna, you can derive the distance between them from propagation loss. Over short distances, several tens to thousand wavelengths, this can work. The procedure is similar like with light- you can measure light intensity at the source and at a distance from it, then, if your light meter is calibrated and "linear", you can derive the distance from the two measurements.
If you use directive antenna at one side, you can also use triangulation, and derive the distance from two triangles. Or, you can locate transmitter and receiver side-by-side, and use radar principle to measure the distance of a remote reflector.

No. Due to various problems- not exactly a free space between antennas, unstable power and/or devices, obstacles, etc. In geography, before laser distance meters were available, microwave echo system was used: on both sides, transceivers were used; one transmitter sent its signal to the opposite receiver, and the transmitter next to it returned the signal to the original point. Pulse delay was thus equal to twice the propagation delay (plus/minus device corrections). Tellurometers as they were named are now obsolete but laser distance meters use a corner mirror on the "other" side, to return the laser pulse to the origin.

Tellurometers as they were named are now obsolete

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any other device available?

laser distance meters use a corner mirror on the "other" side, to return the laser pulse to the origin.

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Is that possible for us to use to calculate distance between two objects even if there are many hard objects placed in between. Also, the two objects may not always in line-of-sight.

thanks

If you utilize the pulsed radar idea, with the transmitter next to the receiver (you can use one common antenna and a switch or two antennas), then you will obtain multiple echoes from all obstacles; the echo from your reflector located at a distance will come last. From the echo delay you can find the distance of the reflector quite well if you know the propagation velocity in a given medium.
To better distinguish the echo from the reflector, you can also modulate its reflectivity and separate other echoes from the "desired" one.

I think the most important in your situation is that you CANNOT determine distance reliably by only using a transmitter at one end and receiver on the other.

If you utilize the pulsed radar idea, with the transmitter next to the receiver....

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Yes. I can use transmitter next to the receiver on both sides. Thats not a problem. My ultimate aim is to measure the distance between Transmitter and Receiver. There may be some hard objects between Transmitter and Receiver and also some times no hard things in between. Distance between Transmitter and Receiver may also varies.

the echo from your reflector located at a distance will come last...

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So, this statement will not always true.

which one is better to use. I have to use PIC MCU for further processing the data.

thanks

If your situation is so complex that you cannot know if the transmitted pulse would ever reach the opposite reflector, I do not see how to use any digital circuits. I would make a model test with an oscilloscope to see and measure real signal patterns, then I would decide how otherwise to design an evaluation system.

As I wrote, you can modulate the opposite reflector to make its echo distinguishable from other , mainly "dense" obstacles. Or you can rotate it like in laser technology, and synchronously detect its echo. Many options are available.

Field strength measurement won't give more than just a order of magnitude for distance I think. Furthermore, with presence of reflecting objects, you'll possibly observe field strength zeros within the Fresnel zone.

State of the art for RF based position detection is time-of-flight respectively phase difference measurement with multiple coupled receivers or transmitters at known fixed positions. It's however also affected by obstacles.

ok. Thanks to both jiripolivka and FvM. I will come with more required details by tomorrow.