Communication Systems & RF Flashcards

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

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

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.

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

Answer: Sky wave propagation

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

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

Answer: 8 kHz

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

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

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

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

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

Answer: To combine two frequencies to produce sum and difference frequencies

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

Which digital modulation scheme transmits the most bits per symbol using both amplitude and phase variations?

Answer: 16-QAM

16-QAM encodes 4 bits per symbol using 16 combinations of amplitude and phase, delivering higher spectral efficiency than BPSK or QPSK.

What does the term 'link budget' calculate in an RF communication system?

Answer: The total accounting of gains and losses between transmitter and receiver

A link budget accounts for all gains (antenna gain, amplifier gain) and losses (path loss, cable loss) to determine if the received signal exceeds the minimum threshold.