physics

On–off keying

On–off keying is a physics 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 On–off keying rather than just read about it. In short: On–off keying (OOK) denotes the simplest form of amplitude-shift keying (ASK) modulation that represents digital data as the presence or absence of a carrier wave. In its simplest form, the presence of a carrier for a specific duration represents a binary one, while its absence for the same duration represents a binary zero.

Key takeaways

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

Reference excerpt

On–off keying (OOK) denotes the simplest form of amplitude-shift keying (ASK) modulation that represents digital data as the presence or absence of a carrier wave. In its simplest form, the presence of a carrier for a specific duration represents a binary one, while its absence for the same duration represents a binary zero. Some more sophisticated schemes vary these durations to convey additional information. It is analogous to unipolar encoding line code. On–off keying is most commonly used to transmit Morse code over radio frequencies (referred to as CW (continuous wave) operation), although in principle any digital encoding scheme may be used. OOK has been used in the ISM bands to transfer data between computers, for example. OOK is more spectrally efficient than frequency-shift keying, but more sensitive to noise when using a regenerative receiver or a poorly implemented superheterodyne receiver. For a given data rate, the bandwidth of a BPSK (Binary Phase Shift keying) signal and the bandwidth of OOK signal are equal. In addition to RF carrier waves, OOK is also used in optical communication systems (e.g. IrDA and fiber-optic communication). In aviation, some possibly unmanned airports have equipment that lets pilots key their VHF radio a number of times in order to request an Automatic Terminal Information Service broadcast, or turn on runway lights. OOK is also used in remote garage and gate keys, often operating at 433.92 MHz, in combination with rolling codes.

References

External links "Application Note 4439 - I'm OOK. You're OOK?". Maxim Integrated. 2009. Archived from the original on 2014-04-22. Retrieved 2014-04-21.

Worked examples

Example 1 — a first encounter with On–off keying

Start with the simplest possible case. Write down what On–off keying claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In physics, 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 On–off keying 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 On–off keying 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 On–off keying

In research: On–off keying appears in physics 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 On–off keying 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: On–off keying is common in secondary-school and first-year university syllabi. It links to neighbouring topics Amateur radio, Fiber-optic communications, Quantized radio modulation modes, so understanding it makes those chapters shorter.
In everyday life: Look for On–off keying 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 On–off keying in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what On–off keying 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 On–off keying out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is On–off keying in simple terms?

Why does On–off keying matter?

Because it connects several physics 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 On–off keying?

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 On–off keying.