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Neets Module 18-Radar Principles | Next
Figure 1-5.—Pulse energy content |
1-7
normal (unambiguous) ranges. The maximum unambiguous range for a given radar system can be
determined by the following formula:
Figure 1-4.—Maximum unambiguous range.
Q3. What is the speed of electromagnetic energy traveling through air?
Q4. How much time is required for electromagnetic energy to travel 1 nautical mile and return to the
source?
Q5. In addition to recovery time, what determines the minimum range of a radar set?
PULSE-REPETITION FREQUENCY AND POWER CALCULATIONS.—The energy content
of a continuous-wave radar transmission may be easily figured because the transmitter operates
continuously. However, pulsed radar transmitters are switched on and off to provide range timing
information with each pulse. The resulting waveform for a transmitter was shown in figure 1-3. The
amount of energy in this waveform is important because maximum range is directly related to transmitter
output power. The more energy the radar system transmits, the greater the target detection range will be.
The energy content of the pulse is equal to the PEAK (maximum) POWER LEVEL of the pulse
multiplied by the pulse width. However, meters used to measure power in a radar system do so over a
period of time that is longer than the pulse width. For this reason, pulse-repetition time is included in the
power calculations for transmitters. Power measured over such a period of time is referred to as
AVERAGE POWER. Figure 1-5 illustrates the way this average power would be shown as the total
energy content of the pulse. The shaded area represents the total energy content of the pulse; the
crosshatched area represents average power and is equal to peak power spread out over the prt. (Keep in
mind, as you look at figure 1-5, that no energy is actually present between pulses in a pulsed radar
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