5. Delaying the AGC by controlling the bias on a diode improves the dynamic rang

Question

5. Delaying the AGC by controlling the bias on a diode improves the dynamic range of a receiver by: A. reducing the gain of larger signals. B. preventing a decrease in sensitivity. C. increasing the selectivity. D. using positive feedback.

6. The noise floor of a receiver is: A. inversely related to the ambient temperature and bandwidth. B. directly related to the bandwidth and the noise figure. C. directly related to noise figure and inversely related to ambient temperature. D. directly related to the ambient temperature and inversely related to bandwidth.

7. A receiver with a noise figure of 20 dB is measured at room temperature to have an output S/N ratio of 10 dB. If the bandwidth is reduced from 2.5 MHz to 200 kHz, the sensitivity will: A. decrease by 10 dB. C. increase by 21 dB. B. increase by 5 dB. D. increase by 22.5 dB.

14. Some advantages of direct digital synthesis are: A. small tuning steps and very fast tuning. B. higher frequency outputs and better phase noise. C. better phase noise and larger tuning steps. D. less expensive and cleaner spectrum.

19. A DDS receiver has a 24-bit phase accumulator and a 102.4 MHz clock frequency. What is the approximate maximum output frequency that can be realized? A. 4.3 MHz C. 102.4 MHz B. 41 MHz D. 409.8 MHz

Explanation / Answer

5. Delaying the AGC by controlling the bias on a diode improves the dynamic range of a receiver by:

Answer: A. Reducing the gain of large signals.

Explanation: AGC can adjusted by reducing the gain of signals with large amplitude. Due to this, the signal to noise ratio (S/N) increases which improves the dynamic range of a receiver.

6. The noise floor of a receiver is:

Answer: B. Directly related to the bandwidth and the noise figure.

Explanation: The input noise for a receiver at room temperature (290K) is -174 dBm/Hz.
Noise floor can then be calculated as:

Noise floor = -174 + NF + 10 log Bandwidth

Where NF is the noise figure.

dBm is the power level expressed in decibels relative to one milliwatt.

Hence we can conclude that Noise floor is directly related to the bandwidth and the noise figure.

14. Some advantages of direct digital synthesis are:

Answer: B. Higher frequency outputs and better phase noise.

Explanation: Higher frequency outputs and better phase noise can be achieved by adjusting the step size.

19. A DDS receiver has a 24-bit phase accumulator and a 102.4 MHz clock frequency. What is the approximate maximum output frequency that can be realized?

Answer: A. 4.3 MHz

Output frequency = Clock frequency/2^n
Here n = number of bits (24 in this case)

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