FOLLOW US ON TWITTER
SHARE THIS PAGE ON FACEBOOK, TWITTER, WHATSAPP ... USING THE BUTTONS ON THE LEFT


YOUR PARTICIPATION FOR THE GROWTH OF PHYSICS REFERENCE BLOG

Saturday, March 27, 2021

The sinusoidal carrier wave has a frequency of 750 kHz and an amplitude of 5.0 V. The carrier wave is frequency modulated by a sinusoidal signal of frequency 7.5 kHz and amplitude 1.5 V.

 Question 9

A carrier wave is frequency modulated.

(a) Describe what is meant by frequency modulation. [2]

 

 

(b) The sinusoidal carrier wave has a frequency of 750 kHz and an amplitude of 5.0 V.

The carrier wave is frequency modulated by a sinusoidal signal of frequency 7.5 kHz and amplitude 1.5 V.

 

The frequency deviation of the carrier wave is 20 kHz V-1.

 

Determine, for the frequency-modulated carrier wave,

(i) the amplitude, [1]

(ii) the minimum frequency, [1]

(iii) the maximum frequency, [1]

(iv) the number of times per second that the frequency changes from its minimum value to its maximum value and then back to the minimum value. [1]

 

 

 

Reference: Past Exam Paper – November 2015 Paper 41 & 42 Q11

 

 

 

Solution:

(a)

Frequency modulation means that the frequency of the carrier wave varies in synchrony with the displacement of the signal (information) wave.

 

 

(b)

(i) 5.0 V          

{In FM, the amplitude does not change but the frequency changes.}

 

(ii) the minimum frequency, [1]

720 kHz

 

{The frequency of the unmodulated carrier wave is 750 kHz.

 

The frequency deviation of the carrier wave is 20 kHz V-1. This means that the (above) frequency can deviate (from its value of 750 kHz) by 20 kHz per volt of the signal wave.

 

1 V - - - > deviation of 20 kHz

The amplitude of the signal wave is 1.5 V.

1 V - - - > deviation of 20 kHz

1.5 V - - - > 1.5 × 20 = 30 kHz

 

So, the frequency of the carrier wave can deviate (can increase or decrease) by up to 30 kHz.

Minimum frequency = 750 – 30 = 720 kHz}

 

(iii) 780 kHz

{Maximum frequency = 750 + 30 = 780 kHz}

 

(iv) 7500

{This is the frequency of the signal wave (= 7.5 kHz = 7500 Hz)}

 

No comments:

Post a Comment

If it's a past exam question, do not include links to the paper. Only the reference.
Comments will only be published after moderation

Currently Viewing: Physics Reference | The sinusoidal carrier wave has a frequency of 750 kHz and an amplitude of 5.0 V. The carrier wave is frequency modulated by a sinusoidal signal of frequency 7.5 kHz and amplitude 1.5 V.