HAM Radio Extra Class Test Modulation and Digital Signals Questions and Answers

Question 1

In digital communications, which modulation technique varies both the phase and the amplitude of the RF carrier to encode data?

Accepted Answer

Quadrature Amplitude Modulation (QAM)

Answer

Phase-Shift Keying (PSK)

Answer

Frequency-Shift Keying (FSK)

Answer

Pulse-Position Modulation (PPM)

Question 2

A digital signal uses 8-PSK modulation. If the symbol rate is 3000 baud, what is the data rate in bits per second (bps)?

Accepted Answer

9000 bps

Answer

3000 bps

Answer

6000 bps

Answer

24000 bps

Question 3

Which of the following is the primary purpose of using Forward Error Correction (FEC) in a digital communication protocol?

Accepted Answer

To allow the receiving station to correct bit errors without retransmission.

Answer

To increase the data rate by compressing the information.

Answer

To encrypt the data for secure communication.

Answer

To reduce the signal bandwidth by using a more efficient encoding scheme.

Question 4

An amateur radio operator is using a digital mode that rapidly changes its operating frequency over a wide band in a pseudo-random sequence known to both the transmitter and receiver. What is the primary advantage of this technique?

Accepted Answer

It is highly resistant to interference and unauthorized detection.

Answer

It concentrates all transmitter power into a single, narrow frequency for maximum range.

Answer

It simplifies receiver design by eliminating the need for a VFO.

Answer

It ensures compatibility with older analog FM equipment.

Question 5

When viewing a constellation diagram for a digitally modulated signal, what does each individual point on the diagram represent?

Accepted Answer

A unique symbol, which may represent one or more bits.

Answer

A single bit of data (a 1 or a 0).

Answer

The overall bit error rate (BER).

Answer

A unique frequency shift of the carrier.

Question 6

In a Software Defined Radio (SDR) that uses the phasing method to generate an SSB signal, what is the relationship between the I (In-phase) and Q (Quadrature) baseband signals?

Accepted Answer

The I and Q signals are 90 degrees out of phase.

Answer

The I and Q signals are identical.

Answer

The Q signal is an inverted version of the I signal.

Answer

The I signal is set to zero, and only the Q channel is modulated.