2 1-9.   When using the reference designator 1A6A4J6, what level does the number 1 refer to? 1.   Subassembly 2.   Assembly 3.   Group 4.   Unit 1-10.   What is the total number of frequency bands the military is currently using for communications? 1.     5 2.     7 3.     9 4. 11 1-11.   Extremely low-frequency transmissions are primarily directed at which of the following users? 1.   Shore installations 2.   Surface ships 3.   Submarines 4.   Aircraft 1-12.   Vlf transmitters are used primarily for which of the following purposes? 1.   Navigation and fleet communications 2.   Frequency standards and time signals 3.   Astronomy and oscillator calibration 4.   Aircraft control and space vehicle tracking 1-13.   Navy use of the low-frequency band is mainly for which, if any, of the following broadcasts? 1.   Ship to shore 2.   Fleet multichannel 3.   Space vehicle telemetry 4.   None of the above 1-14.   For which of the following reasons does the Navy use only the upper and lower ends of the mf band? 1.   They are the most reliable 2.   They produce the best propagation 3.   The commercial fm band occupies the middle 4.   The commercial AM band occupies the middle 1-15.   Hf communications over long-distance trunks, or links between fixed terminals are examples of which of the following types of systems? 1.   Fleet broadcast 2.   Point-to-point 3.   Ground-to-air 4.   Ship-to-shore 1-16.   Sending a message on several frequencies at once is an example of which of the following transmission types? 1.   Time-diversity 2.   Phase-diversity 3.   Distance-diversity 4.   Frequency-diversity 1-17.   What type of diversity uses physically separated transmit or receive antennas to improve communications? 1.   Time 2.   Phase 3.   Space 4.   Frequency 1-18.   Normally the transmission range of vhf is limited to line of sight.  What technique is used to increase this range? 1.   Tropospheric scatter 2.   Atmospheric diversity 3.   Ionospheric maneuvering 4.   Each of the above