HAM Modulation and Digital Signals 2

Question 1

What is the purpose of pre-emphasis in an FM transmitter?

Accepted Answer

To increase the deviation of higher audio frequencies before transmission

Answer

Pre-emphasis boosts higher audio frequencies before transmission to improve the signal-to-noise ratio, and de-emphasis at the receiver restores flat frequency response.

Question 2

Which modulation method conveys information by varying the timing of pulses relative to a reference clock?

Accepted Answer

Pulse position modulation (PPM)

Answer

Pulse position modulation (PPM) encodes information in the time displacement of each pulse from a fixed reference position.

Question 3

In a phase-locked loop (PLL) frequency synthesizer, what does the voltage-controlled oscillator (VCO) output frequency depend on?

Accepted Answer

The DC control voltage from the loop filter

Answer

The VCO output frequency is controlled by a DC voltage produced by the loop filter, which integrates the phase detector error signal.

Question 4

What is the principal advantage of using OFDM (Orthogonal Frequency-Division Multiplexing) in digital HF communications?

Accepted Answer

It is highly resistant to multipath fading and selective fading

Answer

OFDM spreads data across many narrow subcarriers that are orthogonal to each other, making the signal robust against multipath and frequency-selective fading common on HF.

Question 5

What does the term 'frequency deviation' refer to in FM modulation?

Accepted Answer

The peak change in instantaneous carrier frequency from the unmodulated carrier frequency

Answer

Frequency deviation is the maximum instantaneous shift of the carrier frequency above or below the rest frequency, determined by the amplitude of the modulating signal.

HAM - Radio Extra Class Test Practice Test

HAM - Radio Extra Class Test Practice Test

HAM Modulation and Digital Signals 2