engineering

Residual carrier

Residual carrier is a engineering topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Residual carrier rather than just read about it. In short: In analogue TV technology, residual carrier is the ratio of carrier level which is modulated by the maximum video signal to the unmodulated carrier level. Video signal Video signal (VF) or more formally composite video signal (CVS) is the signal which carries the video information as well as some auxiliary signals for synchronizing.

Key takeaways

Residual carrier belongs to engineering; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Residual carrier to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Residual carrier from memory before moving on to harder problems.

Reference excerpt

In analogue TV technology, residual carrier is the ratio of carrier level which is modulated by the maximum video signal to the unmodulated carrier level.

Video signal

Video signal (VF) or more formally composite video signal (CVS) is the signal which carries the video information as well as some auxiliary signals for synchronizing. In all systems 0–300 mV level is reserved for auxiliary signals and 300–1000 mV is reserved for video information. In monochrome TV, 300 mV (or sometimes 350 mV) corresponds to black and 1000 mV corresponds to white.( In color TV depending on the system used, superimposed color subcarrier may have slightly higher values.)

Modulation

The signal modulates a carrier by vestigal sideband modulation (a version of amplitude modulation), where an increase in the video modulating signal produces a decrease in the carrier amplitude, called "negative modulation". When there is no modulating signal, the carrier has the full level and when there is a modulating video frequency (VF) signal the level of IF is lower. Since the level when transmitting a black scene is lower than the white level, the level of carrier when transmitting black is higher than the level of carrier when transmitting white.

The modulators are set to yield 10% or 12.5% of carrier level when modulated by 1 V signal (which corresponds to white scene) This percentage is known as residual carrier. An example of the modulated carrier is shown in the accompanying figure. In this figure, the level of the modulating VF signal is 1 volt (white level). 1 V yields residual carrier (10%). Short duration full carrier (100%) is the sync pulse and the 73% is so called back porch (black level). The duration of the signal is approximately 100 μs.

See also Carrier wave White clipper Zero reference pulse

References and notes

Worked examples

Example 1 — a first encounter with Residual carrier

Start with the simplest possible case. Write down what Residual carrier claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In engineering, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Residual carrier before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Residual carrier ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Residual carrier

In research: Residual carrier appears in engineering research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Residual carrier in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Residual carrier is common in secondary-school and first-year university syllabi. It links to neighbouring topics Broadcast engineering, Television technology, so understanding it makes those chapters shorter.
In everyday life: Look for Residual carrier outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Residual carrier in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Residual carrier means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Residual carrier out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Residual carrier in simple terms?

In analogue TV technology, residual carrier is the ratio of carrier level which is modulated by the maximum video signal to the unmodulated carrier level. Video signal Video signal (VF) or more formally composite video signal (CVS) is the signal which carries the video information as well as some a…

Why does Residual carrier matter?

Because it connects several engineering ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Residual carrier?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Residual carrier.