13 2-45.   Keep-alive voltage is applied to the tr tube for which of the following reasons? 1.    To maintain ionization within the tube after the breakdown voltage is removed 2.    To ensure that the tube will rapidly return to the deionized state 3.    To maintain a glow discharge within the tube so that firing will occur rapidly 4.    To prevent breakdown within the tube prior to pulse transmission so that firing will not be premature 2-46.   Atr tubes generally have a longer duty life than tr tubes because atr tubes do NOT use 1.    radioactive materials and chemically active gas 2.    chemically active gas and keep-alive voltages 3.    keep-alive voltages and radioactive materials 4.    keep-alive voltages and pure inert gas 2-47.   In a series-connected duplexer, what spark gap, if any, fires during reception? 1.     The tr only 2.     The atr only 3.     Both the tr and atr 4.     None of the above 2-48.   Indirectly coupled waveguide duplexers are normally connected to the main waveguide by which of the following devices? 1.     A two-wire line 2.     A coaxial cable 3.     A short quarter-wave stub 4.     A short section of waveguide 2-49.   The direct-coupled waveguide duplexer is connected to the waveguide at the location of 1.     minimum current flow 2.     minimum magnetic field intensity 3.     maximum magnetic field intensity 4.     maximum electric field intensity 2-50.   In a hybrid-ring duplexer, the fields at the entrance of an arm must have what phase relationship to propagate energy down the arm? 1.         0 degrees 2.       90 degrees 3.     180 degrees 4.     270 degrees 2-51.   Which of the following are requirements of a microwave receiver? 1.    Amplify extremely high-frequency pulses 2.    Detect and amplify pulses in the microvolt range 3.    Detect pulses with a duration of a few microseconds 4.    All of the above 2-52.   The maximum range at which a radar receiver can detect an object is limited by which of the following factors? 1.     Noise 2.     Signal distortion 3.     Receiver bandwidth 4.     Transmitter frequency 2-53.   An effective radar receiver should have a gain factor that is in which of the following ranges? 1. 10¹ to 10² 2. 10³ to 10⁴ 3. 10⁶ to 10⁸ 4. 10⁹ to 10¹⁰