14190_23

1-11 The number of strikes per antenna revolution is referred to as HITS PER SCAN. During each revolution enough pulses must be transmitted to return a usable echo. NOTE: The more pulses transmitted to a given area (at slower antenna speeds), the greater the number of hits per scan. As an example, if the antenna rotates at 20 rpm, it completes a revolution in 3 seconds. During this time, a transmitter with a prf of 200 pulses per second (pps) transmits 600 pulses. Since 360 degrees of azimuth must be covered, the following formula shows the number of pulses for each degree of azimuth: Such a low number of pulses for any given target area greatly increases the likelihood that some targets will be missed entirely; therefore, prf and antenna speed must be matched for maximum efficiency. Q6. Atmospheric interference with the travel of electromagnetic energy increases with what rf energy characteristic? Q7. How is prt related to prf? Q8. What type of radar transmitter power is measured over a period of time? Q9. What term is used to describe the product of pulse width and pulse-repetition frequency? BEARING The TRUE BEARING (referenced to true north) of a radar target is the angle between true north and a line pointed directly at the target. This angle is measured in the horizontal plane and in a clockwise direction from true north. The bearing angle to the radar target may also be measured in a clockwise direction from the centerline of your own ship or aircraft and is referred to as the RELATIVE BEARING. Both true and relative bearing angles are illustrated in figure 1-8. Figure 1-8.—True and relative bearings.