Cavity Wavemeter

2-16 Although many wavemeters are used in performing various functions, the cavity-type wavemeter is the type most commonly used. Only this type is discussed in some detail. Cavity Wavemeter Figure 2-12 shows a typical CAVITY WAVEMETER. The wavemeter is of the type commonly used for the measurement of microwave frequencies. The device uses a resonant cavity. The resonant frequency of the cavity is varied by means of a plunger, which is mechanically connected to a micrometer mechanism. Movement of the plunger into the cavity reduces the cavity size and increases the resonant frequency. Conversely, an increase in the size of the cavity (made by withdrawing the plunger) lowers the resonant frequency. The microwave energy from the equipment being tested is fed into the wavemeter through one of two inputs, A or B. The crystal rectifier then detects (rectifies) the signal. The rectified current is indicated on current meter M. Figure 2-12.—Typical cavity wavemeter. Electronic Frequency Counters Another device used to measure frequencies above the audio range is the ELECTRONIC FREQUENCY COUNTER. Since this instrument will be covered in detail in a later chapter, only a brief description is provided at this time. The electronic frequency counter is a high-speed electronic counter with an accurate, crystal- controlled time base. This combination provides a frequency counter that automatically counts and displays the number of events occurring in a precise time interval. The frequency counter itself does not generate any signal; it merely counts the recurring pulses fed to it.