--- title: "VSB generation; VSB for TV; SSB applications" subject: "Communication Systems" chapter: 2 key: "semester_6/communication_systems:vsb-generation-tv-ssb-applications" source: https://www.bctengineer.com/q/semester_6/communication_systems/vsb-generation-tv-ssb-applications site: BCT Engineering --- # VSB generation; VSB for TV; SSB applications Communication Systems · Chapter 2: Amplitude Modulation - Asked in: 2076 Baisakh (CS I), 4+2+2 marks - Video: [Vestigial Sideband (VSB) Modulation Explained](https://www.youtube.com/watch?v=poYG4yNGlEk) — ALL ABOUT ELECTRONICS - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_6/communication_systems/vsb-generation-tv-ssb-applications - Whole chapter: https://www.bctengineer.com/md/semester_6/communication_systems/chapter-2 ## Question Explain about generation of Vestigial Side Band (VSB) AM with its frequency spectrum. Why is VSB suitable for television transmission? Write application areas of Single Side Band (SSB) communication. ## Short answer VSB generated by filtering DSB-SC with a shaping filter that passes one sideband fully and a vestige of the other, with odd symmetry about fc for distortion-free detection; bandwidth = W+fv. VSB suits TV because video has large bandwidth and low-frequency content; SSB filter can't cut sharply at fc, DSB needs double bandwidth. VSB saves bandwidth (e.g., 7MHz channel) and allows envelope detection with added carrier. SSB applications: HF point-to-point, amateur radio, military/aviation HF, analog telephone FDM, police/mobile radio. ## Answer #### Generation of VSB AM **Vestigial Sideband (VSB)** modulation transmits one sideband almost fully and only a small part (vestige) of the other sideband. It is a compromise between DSB (easy to generate, but wide) and SSB (narrow, but hard to filter). ```text m(t) --> Product --> DSB-SC --> VSB filter --> s_VSB(t) modulator H(f) ^ | Ac cos wc t ``` 1. A product (balanced) modulator gives DSB-SC: $A_cm(t)\cos\omega_ct$. 2. A **VSB shaping filter** $H(f)$ passes the wanted sideband fully and a vestige of the other, with a gradual roll-off around $f_c$. 3. For distortion-free coherent detection, the filter must satisfy $$ H(f + f_c) + H(f - f_c) = \text{constant}, \quad |f| \le W $$ i.e. the filter response is **odd-symmetric about $f_c$** (it passes through half its full value at $f_c$), so the part of the wanted sideband lost near $f_c$ is exactly made up by the vestige of the other sideband. **Spectrum** ```text |H(f)| 1 - ____________________ / | 0.5 - - - - - - * | /| | 0 -----------/-+---+-----------------+----> f fc-fv fc fc+fv fc+W <--roll-off--> vestige of LSB full upper sideband ``` Bandwidth $B_T = W + f_v$, where $f_v$ is the vestige width. #### Why VSB for TV - The video signal has a very large bandwidth (about 4.2–5 MHz) and **significant low-frequency and DC content**. SSB filters cannot cut sharply at $f_c$ without removing these, while DSB would need about 10 MHz. - VSB saves almost half the bandwidth: in CCIR-B, video uses a 5 MHz upper sideband plus a 0.75 MHz vestige, so the channel fits into 7 MHz. - With a carrier added, VSB+C can be detected with a simple **envelope detector** in TV receivers. - Practical filters with a gradual slope are easy to build. #### Applications of SSB - HF point-to-point and ship-to-shore radio telephony. - Amateur (ham) radio voice communication. - Military and aviation HF communication. - Frequency division multiplexing in analog telephone carrier systems. - Police and mobile radio, where power and bandwidth are limited. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. How is VSB generated? A. A square-law device followed by an LPF B. DSB-SC from a product modulator is passed through a VSB shaping filter C. Two balanced modulators with a Hilbert transformer only D. Frequency modulation then limiting Answer: B. The filter passes one sideband fully and a vestige of the other. (Key point: VSB generation) 2. What condition must the VSB filter satisfy? A. H(f) must be a sharp cutoff at fc B. H(f) must be zero near fc C. H(f) must be the same for both sidebands D. H(f + fc) + H(f - fc) = constant, i.e. odd symmetry about fc Answer: D. The vestige lost in one sideband is compensated by the other. (Key point: Filter condition) 3. Why is VSB suitable for TV video? A. Video has large bandwidth and significant low-frequency/DC content that SSB filtering would damage, while DSB wastes bandwidth B. Video has no low-frequency content C. VSB requires no filter D. VSB uses twice the bandwidth of DSB Answer: A. VSB saves nearly half the bandwidth and keeps low frequencies. (Key point: Why VSB for TV) 4. Which is an application of SSB? A. FM broadcasting B. TV video transmission C. HF point-to-point radio telephony D. AM medium-wave broadcasting Answer: C. SSB suits power- and bandwidth-limited links such as HF, amateur and marine radio. (Key point: SSB application) ## Related in Communication Systems - [Compare DSB-AM, DSB-SC, SSB, VSB; SSB by phase discrimination](https://www.bctengineer.com/question.md?key=semester_6%2Fcommunication_systems%3Acompare-am-variants-ssb-phase) — Communication Systems, chapter 2 - [VSB modulation, motivation and use in TV](https://www.bctengineer.com/question.md?key=semester_6%2Fcommunication_systems%3Avsb-motivation-tv) — Communication Systems, chapter 2 - [NBFM spectrum vs AM; Armstrong NBFM generation](https://www.bctengineer.com/question.md?key=semester_6%2Fcommunication_systems%3Anbfm-spectrum-vs-am-armstrong) — Communication Systems, chapter 3 - [Single tone DSB-FC AM in time and frequency domain](https://www.bctengineer.com/question.md?key=semester_6%2Fcommunication_systems%3Asingle-tone-dsbfc-time-freq) — Communication Systems, chapter 2 - [SSB in terms of Hilbert transform; SSB generation](https://www.bctengineer.com/question.md?key=semester_6%2Fcommunication_systems%3Assb-hilbert-derivation-generation) — Communication Systems, chapter 2, asked 3× - [Phase shift method of SSB generation: pros and cons](https://www.bctengineer.com/question.md?key=semester_6%2Fcommunication_systems%3Assb-phase-shift-pros-cons) — Communication Systems, chapter 2, asked 2× ## Related in other subjects - [Band applications and microwave transmission lines](https://www.bctengineer.com/question.md?key=semester_7%2Frf_and_microwave_engineering%3Aband-applications-transmission-lines) — RF and Microwave Engineering, chapter 1 - [Spread spectrum frequency hopping in Bluetooth](https://www.bctengineer.com/question.md?key=semester_5%2Finstrumentation_ii%3Afreq-hopping-bt) — Instrumentation II, chapter 5, asked 2× - [Microwave vs low frequency systems and applications](https://www.bctengineer.com/question.md?key=semester_7%2Frf_and_microwave_engineering%3Amicrowave-vs-low-frequency-systems) — RF and Microwave Engineering, chapter 1, asked 2× - [Short note: Radio frequency spectrum](https://www.bctengineer.com/question.md?key=semester_6%2Fpropagation_and_antenna%3Arf-spectrum-short-note) — Propagation and Antenna, chapter 4, asked 3×