A blocking oscillator only generates a signal for a very short time because during the remainder of the time it's signal is blocked, hence the name.

Range markers are drawn on-screen only at appropriate locations.

Range markers are blocked from appearing at other locations, hence a Blocking Oscillator is the appropriate circuit needed to draw them.

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Range markers on a RADAR display are determined by the timer or timing circuitry within the RADAR system. The timer is responsible for measuring the time taken for the transmitted RADAR pulse to travel to the target and return as an echo. By measuring this time, the RADAR system can calculate the distance to the target and display range markers on the screen.

Mnemonic: "TICK - Timer Indicates Calculated Range"

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If f = frequency, d = distance and c = speed of light, then:

d = c / f

d = 3 x 10^8 / 27000m

d = 11111m

d = (11111 / 1852) nm

d = 6nm

But this is the distance to an object and back, so the distance to the object (in this case the range circle) is:

d = (6 / 2) nm = 3nm and the correct answer is A.

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What would be the frequency of a range ring marker oscillator generating range rings at 10 nautical miles intervals?

8 kHz

The frequency can be calculated using the formula:

Frequency (f) = 1 / Time Period (T)

Where:

• Frequency (f) is measured in Hertz (Hz).
• Time Period (T) is measured in seconds (s).

For a round-trip time period, considering the range interval of 10 nautical miles:

Range Interval = 10 nautical miles ≈ 18,520 meters (since 1 nautical mile ≈ 1852 meters).

Speed of Light ≈ 299,792,458 meters per second or about 1,852,000 nautical miles per second.

Time Period (Round-Trip) = 2 * (Range Interval / Speed of Light)

Time Period (Round-Trip) = 2 * (18,520 / 299,792,458) ≈ 1.2386 × 10^-4 seconds

Frequency = 1 / Time Period (Round-Trip) ≈ 1 / (1.2386 × 10^-4) ≈ 8079.37 Hz, or ≈ 8 kHz

Mnemonic: "Eight at 10"

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If f = frequency, d = distance and c = speed of light, then:

d = c / f

d = 3 x 10^8m / 20000Hz

d = 15000m

d = (15000 / 1852) nm

d = 8nm

But this is the distance to an object and back, so the distance to the object (in this case the range circle) is:

d = (8 / 2) nm = 4nm and the correct answer is C.

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If f = frequency, d = distance and c = speed of light, then:

0.25nm = (0.25 x 1852) m = 463m

and:

f = c / d

f = 3 x 10^8m / 463m

f = 648KHz

But this is the frequency corresponding to a distance to an object and back, so the frequency to a distance to the object (in this case the range circle) is:

f = 648KHz / 2

f = 324KHz and the correct answer is B.

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