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Communication Systems & RF Flashcards

7 cards from real CET practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.

Read the first 7 Communication Systems & RF flashcards as text

  1. What is the 3 dB bandwidth of a bandpass filter?

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

    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.

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

    Answer: Subcarriers are mathematically orthogonal to each other

    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.

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

    Answer: To amplify the weak received signal while adding minimal noise

    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.

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

    Answer: SMA

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

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

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

    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.

  6. What is the main advantage of spread spectrum communication techniques?

    Answer: Resistance to interference and interception by spreading signal energy across a wide bandwidth

    Spread spectrum spreads transmitted energy across a much wider bandwidth than required, making the signal resistant to jamming, interference, and eavesdropping.

  7. In a Yagi-Uda antenna array, what is the function of the director elements?

    Answer: To focus radiated energy in the forward direction

    Director elements in a Yagi are slightly shorter than the driven element and placed in front of it, focusing radiated energy in the forward direction for increased directional gain.