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Q & A: Radio ranging

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Most recent answer: 10/22/2007
Q:
Can radio wave/frequency be used to determine distance between a transmitting and a receiving device?
- Meghan Low (age 15)
Corona Del Mar, Newport Beach, California, USA
A:
Not really frequency so much, but radio, and especially, radar, can be used to find the distance between a transmitter and a receiver.

If a pulse of radio waves is emitted by a transmitter, and the pulse (possibly reflected from a target) is received by a receiver (possibly very close to the emitter), then precise knowledge of the travel time gives a precise measure of the total distance the radio wave traveled. The conversion factor is the speed of light, which is known to high accuracy.

Radar is very commonly used to determine the range (and direction) from the radar tower to airplanes in the air, and also to get the ranges on thunderstorms (especially here in the Midwest).

Frequency shifts of radio waves reflected from moving objects are used to measure their speeds. This is called Doppler radar, and is how police often measure the speeds of cars on the road. It's also used by meteorologists to detect rain.

Tom

(published on 10/22/2007)

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