Question 8-32D4

Range rings on a radar display are generated by an oscillator whose frequency corresponds to the desired distance intervals. Electromagnetic waves travel at approximately $3 \times 10^8$ meters per second in free space. For radar, the signal travels out to the target and back, meaning a round trip. 1. **Distance per nautical mile:** 1 nautical mile (NM) is approximately 1852 meters. 2. **Round-trip distance for 10 NM:** The signal travels $2 \times 10 \text{ NM} = 20 \text{ NM}$. $20 \text{ NM} = 20 \times 1852 \text{ meters} = 37,040 \text{ meters}$. 3. **Time taken for round trip:** Time = Distance / Speed Time = $37,040 \text{ m} / (3 \times 10^8 \text{ m/s}) \approx 0.00012347 \text{ seconds}$. This is approximately $123.47 \mu s$. 4. **Frequency of the oscillator:** Frequency = 1 / Time Frequency = $1 / 0.00012347 \text{ s} \approx 8099 \text{ Hz}$. Rounding this value, the frequency is approximately 8 kHz. This oscillator's output provides the timing pulses that create the range rings on the display.