CET Communication Systems & RF 4

Question 1

What does ERP (Effective Radiated Power) represent in RF communications?

Accepted Answer

The transmitter output power multiplied by the antenna gain relative to a dipole

Answer

ERP is the product of the transmitter output power and the antenna gain referenced to a half-wave dipole, representing the effective power in the main beam direction.

Question 2

Which RF propagation mode is used for long-distance HF communications by reflecting signals off the ionosphere?

Accepted Answer

Sky wave propagation

Answer

Sky wave propagation uses the ionosphere to refract HF signals back to Earth, enabling long-distance communication beyond the line-of-sight horizon.

Question 3

What is the Nyquist sampling theorem's minimum sampling rate for a signal with a maximum frequency of 4 kHz?

Accepted Answer

8 kHz

Answer

The Nyquist theorem requires a sampling rate of at least twice the highest frequency component, so 4 kHz × 2 = 8 kHz minimum.

Question 4

In RF systems, what does 'noise figure' quantify?

Accepted Answer

The degradation of signal-to-noise ratio through a device

Answer

Noise figure measures how much a component (amplifier, mixer, etc.) degrades the signal-to-noise ratio, expressed in dB.

Question 5

What is the primary function of an RF mixer in a receiver?

Accepted Answer

To combine two frequencies to produce sum and difference frequencies

Answer

An RF mixer multiplies two input signals (RF and local oscillator), producing output signals at the sum and difference of the input frequencies.

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CET Communication Systems & RF 4