science

Modulated continuous wave

Modulated continuous wave is a science 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 Modulated continuous wave rather than just read about it. In short: Modulated continuous wave (MCW) is Morse code telegraphy transmitted using an audio tone to modulate a carrier wave. Continuous wave (CW), by contrast, does not use a subcarrier, so there is no emission at all between Morse code symbols.

Key takeaways

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

Reference excerpt

Modulated continuous wave (MCW) is Morse code telegraphy transmitted using an audio tone to modulate a carrier wave. Continuous wave (CW), by contrast, does not use a subcarrier, so there is no emission at all between Morse code symbols. MCW can be generated by any AM or FM radio transmitter with audio input from an audio oscillator or equivalent audio source. When an SSB transmitter is modulated by Morse code of only a single audio frequency, the resulting radio frequency emission is J2A or J2B and therefore is CW by definition, not MCW.

Amplitude Modulation (AM) MCW on AM would typically be sent as double-sideband amplitude modulation, with one channel containing digital information, and using a subcarrier, also known as A2A. For example, Morse code sent in an AM broadcast by a commercial radio station would be modulated CW as it contains a subcarrier. This mode is designated A2A by the Federal Communications Commission. The symbols stand for: A (amplitude modulation), 2 (one channel containing digital information, using a subcarrier), A (aural telegraphy). Single-sideband modulation with full carrier (H2A/H2B) is another form of modulated CW (MCW). Amateur radio operators may also use A2A to transmit Morse code, however it would be more typical to send it as CW, rather than MCW, using single-sideband modulation with a suppressed carrier, which reduces the bandwidth and power requirements. The FCC designates this mode as either aural telegraphy (J2A) if intended to be decoded by ear, or otherwise as electronic telegraphy (J2B), if it's intended to be decoded by machine). Unlike A1A CW transmissions (double sideband, with no subcarrier), A2A MCW will produce an audible audio tone from an AM radio receiver that is not equipped with a beat oscillator. MCW is commonly used by RDF beacons to transmit the station identifier.

Frequency Modulation (FM) When Morse code is transmitted using frequency modulation (FM), it is a form of MCW. The FCC designates this mode as F2A: F (frequency modulation), 2 (one channel containing digital information, using a subcarrier), A (aural telegraphy). F2A MCW Morse can be heard on a normal FM radio receiver, and it is commonly used by both commercial and amateur repeater stations for identification. Also, F2A is sometimes used by other types of stations operating under automatic control, such as a telemetry transmitter or a remote base station.

Classification and other forms

In the United States, the Federal Communications Commission defines modulated continuous wave in 47 CFR §97.3(c)(4) as "Tone-modulated international Morse code telegraphy emissions having designators with A, C, D, F, G, H or R as the first symbol; 2 as the second symbol; A or B as the third symbol." These symbols are defined by the International Telecommunication Union. The FCC classifies International Morse code telegraphy emissions as "digital information". All Modulated CW (MCW) emission types listed by the FCC (all are one channel and use a subcarrier):

Double-sideband amplitude modulation (A2A, A2B) – e.g. AM broadcast radio Vestigial sideband (C2A, C2B) Combination of AM and FM or PM (D2A, D2B) Frequency modulation (F2A, F2B) — e.g. FM broadcast radio Phase modulation (G2B) Single-sideband modulation with full carrier (H2A, H2B) Single-sideband with reduced or variable carrier (R2A, R2B). All CW emission types (not MCW), listed by the FCC (all are one channel):

Double-sideband amplitude modulation, no subcarrier (A1A, A1B) Vestigial sideband, no subcarrier (C1A, C1B) Single-sideband modulation with full carrier, no subcarrier (H1A, H1B) Single-sideband with suppressed carrier, no subcarrier (J1A, J1B) Single-sideband with suppressed carrier, with subcarrier (J2A, J2B) Single-sideband with reduced or variable carrier, no subcarrier (R1A, R1B)

See also Morse code Prosigns for Morse code Types of radio emissions On–off keying

References

"Amateur Radio Service Definitions (47 CFR §97.3)". Retrieved August 3, 2005. "Ham Radio Jargon, Abbreviations and Terminology". Archived from the original on September 19, 2017. Retrieved August 3, 2005.

Worked examples

Example 1 — a first encounter with Modulated continuous wave

Start with the simplest possible case. Write down what Modulated continuous wave claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, 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 Modulated continuous wave 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 Modulated continuous wave 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 Modulated continuous wave

In research: Modulated continuous wave appears in science 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 Modulated continuous wave 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: Modulated continuous wave is common in secondary-school and first-year university syllabi. It links to neighbouring topics Amateur radio stubs, Morse code, Radio modulation modes, so understanding it makes those chapters shorter.
In everyday life: Look for Modulated continuous wave 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 Modulated continuous wave in 20 minutes

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

Frequently asked questions

What is Modulated continuous wave in simple terms?

Why does Modulated continuous wave matter?

Because it connects several science 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 Modulated continuous wave?

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 Modulated continuous wave.