HAM Modulation and Digital Signals 5

Question 1

What is the significance of Carson's rule in FM signal analysis?

Accepted Answer

It provides an approximation of the bandwidth occupied by an FM signal as 2(Δf + fm)

Answer

Carson's rule approximates FM bandwidth as twice the sum of the peak deviation and the highest modulating frequency, capturing about 98% of the signal power.

Question 2

What is a major difference between Gaussian Minimum Shift Keying (GMSK) and standard MSK?

Accepted Answer

GMSK passes the data through a Gaussian filter before modulation, reducing spectral occupancy and sidelobes

Answer

GMSK applies a Gaussian low-pass filter to the data stream before MSK modulation, smoothing transitions and greatly reducing out-of-band spectral emissions.

Question 3

What happens to an FM receiver's capture effect when two signals are present on the same frequency?

Accepted Answer

The stronger signal suppresses the weaker one, with the receiver locking to the stronger signal

Answer

FM's capture effect causes the receiver to lock onto the stronger of two co-channel signals and largely reject the weaker one, unlike AM where both signals mix audibly.

Question 4

In direct digital synthesis (DDS), what determines the output frequency of the synthesizer?

Accepted Answer

The phase increment value loaded into the phase accumulator register

Answer

A DDS generates a frequency by repeatedly adding a phase increment to a phase accumulator; larger increments produce higher frequencies from the same reference clock.

Question 5

What is the primary purpose of a raised cosine filter in a digital communications system?

Accepted Answer

To minimize intersymbol interference by shaping pulses so they have zero crossings at adjacent symbol intervals

Answer

A raised cosine filter shapes each transmitted symbol pulse so it reaches zero exactly at the sampling instants of adjacent symbols, preventing ISI without excess bandwidth.

HAM - Radio Extra Class Test Practice Test

HAM - Radio Extra Class Test Practice Test

HAM Modulation and Digital Signals 5