# Measure distance of devices via radio?

1. Jan 11, 2010

### ghubben

Hello,

I've got a question about distance measuring via radio.
I would like to measure the distance between two devices, relatively small ones, using radio and my question is how fine that measurement can be? The devices would be a maximum of say 15 metres apart and a preciseness of about a millimeter is needed. Is that possible with common circuits available?

I'm not an electrical engineer of any sort so please keep it in laymans terms.

Thanks!
//Fredrik

2. Jan 11, 2010

### vk6kro

I don't think you could expect that sort of accuracy from radio signals.

The problem is that radio signals travel VERY FAST.

The speed of light and radio waves is 300 000 000 meters a second.
So, that is 300 meters a microsecond and 0.3 meters or 300 mm per nanosecond.

And the best logic circuits we have are capable of operating at the nanosecond level.

Even then it would be a very difficult project.

There might be a low tech solution using a video camera above both objects, but the answer to your question is no, unfortunately.

Ultrasonics may be another way. A sound wave travels at about 340 meters a second.
That is about 0.34 millimeters per microsecond.
So, you could send out a radio signal that a sound pulse was on its way and then count the time until the sound pulse got to the second object.
The radio signal would take a negligible time to get there, so quite an accurate reading could be obtained.

Developing something like that would take time and expertise though.

3. Jan 11, 2010

### ramonegumpert

Hi Fredrik,

Sorry, i am not the expert you looking for but just happen to see your posting and like to share some info with you.

What i know is that ultrasonic promixity sensors used by cars and robots can detect objects upto as near as 2cm, as shown in this webpage :

http://www.parallax.com/Store/Senso...efault.aspx?SortField=ProductName,ProductName

Unfortunately, i do not know how can it detect proximity changes as small a millimeter. Personally, i do not think it can as car sensors are not that sensitive, i suspect.

4. Jan 11, 2010

### Staff: Mentor

Lasers night be a possibility. The resolution of radar is limited to the wavelength of the signal.