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2-13 Figure 2-7.—Modulator charging impedance. Many different kinds of charging impedance and charging circuits are used in radar modulators. The type of charging impedance and charging circuit used depends on the following five elements: 1. The type of power supply (ac or dc) 2. The type of storage element 3. The amount of modulator pulse voltage required 4. The pulse-repetition rate 5. The frequency of the available ac supply voltage Q16. What type of tube best meets the requirements of a modulator switching element? Q17. What modulator element controls the rate at which the storage element charges? KEYED-OSCILLATOR TRANSMITTER The KEYED-OSCILLATOR TRANSMITTER most often uses a MAGNETRON as the power oscillator. The following discussion is a description of a magnetron used as a keyed-oscillator radar transmitter. Figure 2-8 shows the typical transmitter system that uses a magnetron oscillator, waveguide transmission line, and microwave antenna. The magnetron at the bottom of the figure is connected to the waveguide by a coaxial connector. High-power magnetrons, however, are usually coupled directly to the waveguide. A cutaway view of a typical waveguide-coupled magnetron is shown in figure 2-9.