# Radar Questions and Answers – Receiver Noise and SNR Ratio

This set of Radar Multiple Choice Questions & Answers (MCQs) focuses on “Receiver Noise and SNR Ratio”.

1. Which noise is generated in the ohmic region of the receiver input stage?
a) Intermodulation noise
b) Impulse noise
c) Thermal noise
d) Shot noise

Explanation: The thermal noise is generated at the receiver input stage. It’s because in the entire frequency spectrum thermal noise is dispersed uniformly, so even though the receiver itself is perfect including a noise free surrounding, there will still be noise generated which is nothing but thermal noise.

2. The magnitude of Johnson’s noise is directly proportional to the bandwidth and the absolute temperature.
a) True
b) False

Explanation: Thermal noise or Johnson’s noise generated at the input of a receiver with bandwidth and temperature can be written as, available thermal noise power = kTBn.

3. What is the value of Boltzmann’s constant?
a) 1.38 x 10-23 J/deg
b) 1.27 x 10-29 J/deg
c) 1.49 x 10-31 J/deg
d) 1.32 x 10-24 J/deg

Explanation: Boltzmann’s constant is represented by k and its value is 1.38 x 10-23 J/deg. It was named after Ludwig Boltzmann which is used to relate temperature to energy and it is a crucial tool in both classical and quantum physics.

4. The bandwidth whose noise power output is the same as the filter with frequency response function is known as _______
a) dual filter bandwidth
b) power bandwidth
c) full power bandwidth
d) noise bandwidth

Explanation: Noise bandwidth is the bandwidth of the equivalent rectangular filter whose noise power output is the same as the filter with frequency response function H (f). It is not the same as the more familiar half power, or 3 dB, bandwidth.

5. The ratio of noise output of a practical receiver to the noise output of an ideal receiver at standard temperature is called as ___________
a) Noise figure
b) Noise factor
c) SNR ratio
d) Probability Density Function

Explanation: The noise output of a real (practical) receiver to that from the ideal receiver with only thermal noise is called as noise figure which is given by, Fn = Nout/KTOBGa.

6. Why is noise figure defined in terms of standard temperature only?
a) It reduces thermal agitation noise
b) It improves signal to noise ratio
c) It assures uniformity in measurements
d) It increases available gain

Explanation: IEEE defines standard temperature TO as 290K (62°F) which is close to room temperature. So, standard assures uniformity in measurement that might be made at different temperatures.

7. In radar range equation, the minimum detectable signal is replaced by ________
a) receiver noise figure
b) maximum unambiguous signal
c) maximum detectable SNR
d) minimum detectable SNR

Explanation: In radar range equation, the minimum detectable signal is replaced by a minimum detectable signal to noise ratio which is independent of the receiver bandwidth and noise figure.

8. The half power bandwidth B is usually used to approximate the noise bandwidth Bn.
a) True
b) False

Explanation: Half power bandwidth is the separation between the points of the H (f) where the response is reduced 0.707 from its maximum value. Even though it is not the same as the noise bandwidth, it is still reasonable approximation for many practical radar receiver.

9. The ratio of signal out, Sout to the signal is, Sin is known as _______
a) SNR ratio
b) Available gain
c) Effective bandwidth
d) Frequency response

Explanation: The ratio of signal out to signal in is known as available gain where both the output and input matched to deliver maximum output power.

10. Why is it necessary to maximize the signal to noise ratio at the output of IF amplifier?
a) To maximize the video output
b) To maximize max power transfer
c) To reduce the noise components
d) To maintain uniformity of signal

Explanation: The signal to noise ratio in the radar range equation is present at the output of the IF amplifier because maximizing the SNR at the output of the IF is equivalent to the video output where the threshold decision is made.

Sanfoundry Global Education & Learning Series – Radar.

To practice all areas of Radar, here is complete set of Multiple Choice Questions and Answers.

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