1
What is the primary advantage of Single Sideband (SSB) modulation over standard AM?
Higher power efficiency
Reduced bandwidth requirements
Simpler receiver design
Better resistance to multipath fading
SSB modulation requires only half the bandwidth of standard AM. While AM requires bandwidth equal to twice the highest modulating frequency (BW = 2fm ), SSB requires only the bandwidth of the message signal itself (BW = fm ). This is achieved by transmitting only one sideband and suppressing both the carrier and the other sideband.
2
In SSB modulation, which mathematical operation is essential for generating the signal?
Fourier Transform
Laplace Transform
Hilbert Transform
Z-Transform
The Hilbert Transform is essential for SSB generation. It provides a 90-degree phase shift to all frequency components of the message signal. The SSB signal can be expressed as:
sSSB (t) = m(t)cos(2πfc t) ∓ m̂(t)sin(2πfc t)
Where m̂(t) is the Hilbert Transform of m(t). The minus sign produces the Upper Sideband (USB), while the plus sign produces the Lower Sideband (LSB).
3
What is the bandwidth required for an SSB signal when the modulating signal has frequencies from 300 Hz to 3.4 kHz?
3.1 kHz
6.2 kHz
3.4 kHz
6.8 kHz
SSB requires bandwidth equal to the bandwidth of the modulating signal. For a voice signal with frequency components from 300 Hz to 3.4 kHz:
4
Why is coherent detection necessary for demodulating SSB signals?
To suppress the carrier
To separate the sidebands
To compensate for the Hilbert transform
To reinsert the suppressed carrier
SSB signals are demodulated using coherent detection because:
The carrier is suppressed during transmission to save power
The receiver must reinsert a carrier at the correct frequency and phase
Demodulation is achieved by multiplying the SSB signal with a locally generated carrier
The original message is recovered after low-pass filtering
Mathematically: sd (t) = sSSB (t) · cos(2πfc t) → LPF → m(t)
5
What happens if there's a phase error in the local oscillator during SSB coherent detection?
Increased bandwidth
Signal attenuation
Distortion in the demodulated signal
Complete signal loss
Phase errors in the local oscillator cause distortion in SSB demodulation:
For voice signals: Creates a "Donald Duck" effect
For data signals: Causes bit errors
Mathematically, the output is: mout (t) = ½[m(t)cosθ - m̂(t)sinθ]
When θ ≠ 0, the Hilbert transform component appears in the output
Frequency errors shift the pitch of voice signals
6
Which method is commonly used to generate SSB signals without requiring sharp filters?
Envelope elimination and restoration
Phase-shift method
Synchronous detection
Frequency discrimination
The phase-shift method generates SSB without sharp filters:
7
What is the purpose of a pilot carrier in some SSB systems?
To increase transmission power
To provide a reference for coherent detection
To improve signal-to-noise ratio
To reduce bandwidth further
A pilot carrier is a low-level carrier transmitted alongside the SSB signal:
Provides a frequency and phase reference for the receiver
Enables accurate carrier regeneration using PLLs
Typically 10-20 dB below peak envelope power
Used in broadcast applications and some point-to-point systems
Compromise between pure SSB (no carrier) and DSB (full carrier)
8
In which frequency bands is SSB modulation most commonly used?
MF (Medium Frequency) broadcast band
HF (High Frequency) shortwave band
UHF television bands
Microwave satellite links
SSB is predominantly used in HF bands (3-30 MHz) because:
Bandwidth efficiency is critical in crowded HF spectrum
Long-distance propagation via ionospheric reflection
Applications: Maritime, aviation, amateur radio, military communications
Power efficiency important for battery-operated equipment
Less affected by selective fading than AM
SSB is also used in some VHF/UHF applications, but its primary domain is HF communications.
9
What is the main challenge in implementing the filter method of SSB generation?
Generating the carrier signal
Designing filters with sharp cutoff characteristics
Achieving linear amplification
Synchronizing the receiver
The filter method requires extremely sharp filters because:
The sidebands are separated by only 2fmin (e.g., 600 Hz for voice)
To suppress the unwanted sideband by 40-60 dB
Conventional filters (LC, RC) can't achieve the required shape factor
Solutions:
Crystal filters: High Q, sharp cutoff
Mechanical filters: Precise frequency response
Phasing method: Avoids need for sharp filters
Weaver's method: Improved phasing approach
10
How does SSB compare to FM in terms of noise performance?
SSB has better noise performance than FM
FM has better noise performance than SSB
Both have similar noise performance
Noise performance depends on frequency band
FM generally has superior noise performance compared to SSB:
FM exhibits a capture effect that suppresses weaker interfering signals
FM has a threshold effect - above certain SNR, noise is greatly suppressed
SSB is more susceptible to noise since information is in amplitude variations
Trade-offs:
FM requires more bandwidth (WBFM: 2(Δf + fm ))
SSB is more bandwidth-efficient
FM receivers are simpler than SSB coherent detectors
In practice, FM is used for high-fidelity audio, SSB for spectrum efficiency