2-38
Figure 2-35D.—Magnetron coupling methods.
Figure 2-35E.—Magnetron coupling methods.
MAGNETRON TUNING.—A tunable magnetron permits the system to be operated at a precise
frequency anywhere within a band of frequencies, as determined by magnetron characteristics.
The resonant frequency of a magnetron may be changed by varying the inductance or capacitance of
the resonant cavities. In figure 2-36, an inductive tuning element is inserted into the hole portion of the
hole-and-slot cavities. It changes the inductance of the resonant circuits by altering the ratio of surface
area to cavity volume in a high-current region. The type of tuner illustrated in figure 2-36 is called a
SPROCKET TUNER or CROWN-OF-THORNS TUNER. All of its tuning elements are attached to a
frame which is positioned by a flexible bellows arrangement. The insertion of the tuning elements into
each anode hole decreases the inductance of the cavity and therefore increases the resonant frequency.
One of the limitations of inductive tuning is that it lowers the unloaded Q of the cavities and therefore
reduces the efficiency of the tube.
