Question:
A carrier wave of frequency \(2\,MHz\) and peak voltage \(15\,V\) is used to modulate a message signal of frequency \(20\,kHz\) and peak voltage \(8\,V\). The frequencies of side bands produced are
A carrier wave of frequency \(2\,MHz\) and peak voltage \(15\,V\) is used to modulate a message signal of frequency \(20\,kHz\) and peak voltage \(8\,V\). The frequencies of side bands produced are
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In amplitude modulation:
\[
\text{Side bands}=f_c\pm f_m
\]
Always keep carrier and message frequencies in same units before substitution.
Updated On: Jun 17, 2026
- \(2000\,kHz,\,20\,kHz\)
- \(2020\,kHz,\,1980\,kHz\)
- \(2040\,kHz,\,1960\,kHz\)
- \(2020\,kHz,\,2000\,kHz\)
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The Correct Option is B
Solution and Explanation
Concept:
In amplitude modulation:
\[
f_{USB}=f_c+f_m
\]
\[
f_{LSB}=f_c-f_m
\]
where:
• \(f_c\) = carrier frequency
• \(f_m\) = message frequency
Step 1: Convert frequencies into same units. Carrier frequency: \[ f_c=2MHz=2000kHz \] Message frequency: \[ f_m=20kHz \]
Step 2: Calculate upper side band frequency. \[ f_{USB}=2000+20 \] \[ f_{USB}=2020kHz \]
Step 3: Calculate lower side band frequency. \[ f_{LSB}=2000-20 \] \[ f_{LSB}=1980kHz \] Hence the side band frequencies are: \[ \boxed{2020\,kHz,\ 1980\,kHz} \]
• \(f_c\) = carrier frequency
• \(f_m\) = message frequency
Step 1: Convert frequencies into same units. Carrier frequency: \[ f_c=2MHz=2000kHz \] Message frequency: \[ f_m=20kHz \]
Step 2: Calculate upper side band frequency. \[ f_{USB}=2000+20 \] \[ f_{USB}=2020kHz \]
Step 3: Calculate lower side band frequency. \[ f_{LSB}=2000-20 \] \[ f_{LSB}=1980kHz \] Hence the side band frequencies are: \[ \boxed{2020\,kHz,\ 1980\,kHz} \]
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