HAM Modulation and Digital Signals 3

Question 1

What is the significance of the 'eye pattern' in evaluating digital signal quality?

Accepted Answer

It reveals intersymbol interference, noise, and timing jitter in a digital data stream

Answer

An eye pattern (eye diagram) is formed by overlaying successive bit intervals on an oscilloscope; a wide-open eye indicates low ISI and noise, while a closed eye indicates problems.

Question 2

What is the deviation ratio of an FM signal?

Accepted Answer

The ratio of the maximum frequency deviation to the highest modulating frequency

Answer

Deviation ratio equals peak frequency deviation divided by the highest audio frequency, and it determines the modulation index under worst-case conditions.

Question 3

In 8-PSK modulation, how many bits are encoded per symbol?

Accepted Answer

3 bits

Answer

8-PSK has 8 phase states (2³ = 8), so each symbol carries 3 bits of information.

Question 4

What effect does increasing the modulation index have on an FM signal's bandwidth?

Accepted Answer

Bandwidth increases because additional significant sideband pairs are generated

Answer

Higher modulation index produces more significant Bessel function sideband pairs, which increase the occupied bandwidth of the FM signal.

Question 5

What is the purpose of forward error correction (FEC) in digital communications?

Accepted Answer

To add redundant bits that allow the receiver to detect and correct errors without retransmission

Answer

FEC encodes data with redundancy so the receiver can identify and correct errors autonomously, making it ideal for one-way or high-latency links.

HAM - Radio Extra Class Test Practice Test

HAM - Radio Extra Class Test Practice Test

HAM Modulation and Digital Signals 3