Learning Event 2:
MAGNETRONS.
1.
General.
a. A radar transmitter is made up of two major units, the modulator and
the magnetron. The modulator forms the radar pulse and turns the RF carrier
on and off.
In fact, the modulator acts just like a switch and may
therefore be thought of as a keyer.
b. You have already learned how the modulator develops a radar pulse of
the correct width and amplitude. Now you will learn how this pulse helps to
generate an RF carrier. After this, the next step is to direct the carrier
out into space and search for targets.
c. A different method is used in generating the carrier frequency in a
radar set than is used in a radio set.
The oscillator in a radio
transmitter employs many units to generate the RF, but a radar set uses only
one oscillator unit, the magnetron.
If anything goes wrong with the
magnetron, causing it to stop working, the radar set cannot be used. That's
why the magnetron is so vital to radar set operation. And that's why you
must know how to maintain the magnetron properly.
d. In the first part of this lesson, you will see how a magnetron is
constructed and learn how it works. Then you will learn why the amount of
voltage and strength of the magnetic field applied to a magnetron must
always be correct. Finally, you will learn how to take care of magnetrons,
what troubles they may develop, and how to make some magnetron checks.
2.
Construction of a magnetron.
a. Figure 84 shows two types of magnetrons.
You already know that a
magnetron consists of a diode and a magnet.
Sometimes the magnet is
separate from the tube as in Part A of Figure 84. When the magnet is part
of the tube as in Part B of Figure 84, it is called a packaged magnetron.
b. Some magnetrons, like the one shown in Part A of Figure 84,
oscillate at only a fixed frequency. The magnetron in Part B of Figure 84
is a tunable type which you tune by means of the two gears on top of the
tube.
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