CET Communication Systems & RF 5

Question 1

What is the 3 dB bandwidth of a bandpass filter?

Accepted Answer

The frequency range over which the filter response drops to half its peak power

Answer

The 3 dB bandwidth is the frequency range between the two points where the filter's power response drops to half (−3 dB) of its maximum passband value.

Question 2

In OFDM (Orthogonal Frequency Division Multiplexing), what property allows subcarriers to overlap without interference?

Accepted Answer

Subcarriers are mathematically orthogonal to each other

Answer

OFDM subcarriers are spaced so that each subcarrier's peak coincides with the nulls of all others, making them mathematically orthogonal and free from inter-carrier interference.

Question 3

What is the purpose of a low-noise amplifier (LNA) at the front end of an RF receiver?

Accepted Answer

To amplify the weak received signal while adding minimal noise

Answer

The LNA amplifies the weak incoming RF signal while contributing minimal noise of its own, preserving the signal-to-noise ratio early in the receive chain.

Question 4

Which type of RF connector is most commonly used in precision 50-ohm microwave test equipment up to 18 GHz?

Accepted Answer

SMA

Answer

SMA (SubMiniature version A) connectors are precision 50-ohm connectors commonly rated to 18 GHz, widely used in RF and microwave test equipment.

Question 5

What is 'intermodulation distortion' (IMD) in RF systems?

Accepted Answer

Unwanted frequency products generated when two or more signals pass through a nonlinear device

Answer

IMD occurs when two or more signals interact in a nonlinear device (amplifier, mixer), creating spurious output frequencies at sums and differences of the input frequencies and their harmonics.

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CET Communication Systems & RF 5