How To Create Radio?

How does radar create radio waves?

• okay, so im trying to learn how radar works. so far here is what i have down, and you can fill in the rest for 10 points. radar sends out radio waves, which bounce off an object and are reflected back where they can be measured. using echo and doppler shift you can measure the size, speed, heading of, and distance to a target. i assume the process for creating the radio waves that will eventually bounce off a target is no more complicated than the process of creating light or sound? how are these waves created exactly?

• Answer:

  The type of device used for generating radar signals depends on the type of radar - the wavelength or frequency, the power required, whether the radar is pulsed or continuous wave, etc. But the classic and most used technique is the magnetron. The reference below gives a very good description of the idea. The magnetron is a thermionic device in which electrons emitted by a hot cathode are accelerated in an electric field using a voltage of several thousand volts, and an orthogonal magnetic field which deflects the electrons into a circular path. The circular beam of electrons scans across a series of cavities in a copper block, and excites oscillations in them like blowing across the top of a bottle. Magnetrons operating at 2.45GHz (wavelength 12.5cm) and a continuous power of around 1KW are used in microwave ovens, but other examples can generate short pulses in the MW or 10s of MW range with wavelengths down to the millimetre range, and these are used for radar. The technology is not as simple as producing light or sound, devices for which have been around throughout mankind's history. The magnetron was invented in the 1940s during WW2 as a compact and lightweight device which could be carried on an aircraft and used for detecting submarines, or their periscopes or snorkels; a wavelength of about 10cm was used, which, at first was not detectable by the enemy targets. Prior to the invention of the magnetron, longer wave radars were made using other techniques such as ordinary thermionic valves or klystrons. (google Klystron). Low power continuous wave radars can use Gunn diodes which are a form of semiconductor diode. These are used in burglar alarms operating on the Doppler principle; the reflection from the moving target produces an audio-frequency beat note when mixed with the output of the Gunn diode from the transmitter, and the resulting signal can be processed using AF circuitry. If you want to experiment with radar you should look around for one of these devices - they are fun to play with, and safe since the power is low - only a few 10s of milliwatts.