--- title: "Switching hierarchy and Marconi's transmitter" subject: "Telecommunications" chapter: 1 key: "semester_8/telecommunications:switching-hierarchy-marconi" source: https://www.bctengineer.com/q/semester_8/telecommunications/switching-hierarchy-marconi site: BCT Engineering --- # Switching hierarchy and Marconi's transmitter Telecommunications · Chapter 1: Telecommunication Networks - Asked in: 2073 Shrawan, 4+4 marks - Video: [Marconi Spark Gap Transmitter (4-Analog Electronics)](https://www.youtube.com/watch?v=11ix-jngaPA) — Aaron Danner - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_8/telecommunications/switching-hierarchy-marconi - Whole chapter: https://www.bctengineer.com/md/semester_8/telecommunications/chapter-1 ## Question Draw the switching hierarchy used in telecommunication switching system. Describe the working principle of Marconi's induction coil radio transmitter. ## Short answer Switching hierarchy has class 5 end offices, class 4 toll centres, class 3 primary, class 2 sectional, and class 1 regional centres; calls use high-usage trunks then final route. Marconi's transmitter uses battery, Morse key, induction coil, spark gap, aerial and earth to radiate damped waves; receiver coherer detects Morse code. ## Answer #### Switching hierarchy ```text Class 1: Regional centre / \ Class 2: Sectional Class 2: Sectional centre centre | | Class 3: Primary Class 3: Primary centre centre | | Class 4: Toll centre Class 4: Toll centre / \ | Class 5 Class 5 Class 5 end office end office end office | | | | subscribers subscribers subscribers Final (hierarchical) route: ─── (vertical links) High-usage trunks: direct links between busy offices at any level (shortcuts) ``` - **Class 5** end offices serve subscribers; **Class 4** toll centres connect end offices to the long-distance network; **Class 3, 2, 1** (primary, sectional, regional centres) form the higher levels. - Calls first use **high-usage (direct) trunks**; on overflow they move up the hierarchy and finally use the **final route**. #### Marconi's induction coil radio transmitter Marconi's transmitter (1895–1901) was a **spark-gap transmitter** used for wireless telegraphy (Morse code). ```text Battery ─┬─ Morse key ─┐ │ v │ ┌─────────────┐ spark ┌── Aerial │ │ Induction │──┤gap├────┤ └──────│ coil (Ruhm- │ (balls) │ │ korff) │───────────┴── Earth └─────────────┘ ``` 1. A **battery** and a **Morse key** feed the primary of an **induction (Ruhmkorff) coil**. An interrupter (vibrator) makes and breaks the primary current rapidly. 2. Each interruption induces a very **high voltage** (tens of kV) in the secondary winding. 3. The secondary is connected across a **spark gap** between two metal balls; one side goes to an elevated **aerial (antenna)** and the other to **earth**. 4. When the voltage breaks down the gap, a spark discharges the aerial–earth capacitance, producing **damped high-frequency oscillations** in the aerial, which radiate **electromagnetic waves**. 5. Pressing the key for short or long times sends sparks in dots and dashes, i.e. Morse code. 6. At the receiver, a **coherer** (metal filings tube) became conductive when waves arrived, operating a relay and a Morse inker; a tapper reset it. Marconi's use of a tall grounded aerial greatly increased range, leading to the first transatlantic signal in 1901. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. Which class of office directly serves subscribers in the switching hierarchy? A. Class 1 regional centre B. Class 3 primary centre C. Class 4 toll centre D. Class 5 end office Answer: D. Class 5 end offices serve subscribers; class 4 toll centres link them to the long-distance network. (Key point: Hierarchy levels) 2. How does a call use trunks in the hierarchy? A. Always goes up to the regional centre first B. Tries high-usage direct trunks first, then overflows up the hierarchy to the final route C. Uses only the final route D. Chooses randomly between routes Answer: B. High-usage direct trunks are tried first; on overflow the call moves to the final (hierarchical) route. (Key point: High-usage and final route) 3. How does Marconi's transmitter produce radio waves? A. A continuous sine oscillator feeds the aerial B. The induction coil's high secondary voltage breaks down a spark gap, discharging the aerial-earth capacitance as damped high-frequency oscillations C. The coherer radiates the waves D. The Morse key directly connects the aerial to the battery Answer: B. Each spark discharges the aerial capacitance causing damped HF oscillations that radiate as electromagnetic waves. 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