engineering

Intercarrier method

Intercarrier method 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 Intercarrier method rather than just read about it. In short: The intercarrier method is a system in television that reduces the cost of transmitters and receiver sets by processing audio and video signals together and minimizing the number of separate stages for audio and video signals. Transmission of audio and video signals In television, unlike monophonic radio, at least two signals should be transmitted; audio (AF) and video (VF) signals.

Key takeaways

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

Reference excerpt

The intercarrier method is a system in television that reduces the cost of transmitters and receiver sets by processing audio and video signals together and minimizing the number of separate stages for audio and video signals.

Transmission of audio and video signals In television, unlike monophonic radio, at least two signals should be transmitted; audio (AF) and video (VF) signals. Transmitting those signals by means of separate transmitters and antenna systems is a very costly solution, because every stage must be used twice, one for AF and one for VF. Two separate transmitters, a high power combiner and a common antenna system, known as the split sound system, is also quite costly. But if the signals are combined at an earlier stage, the number of costly outer stages is reduced. The same logic also applies to receiver sets. If the modulated signal is separated just before the picture tube the number of separate stages for AF and VF is minimized. This common signal processing system is known as the intercarrier system.

Intercarrier as used in TV transmitters

In TV transmitters, both AF and VF modulate intermediate frequency (IF) carriers. (The frequency difference between the two carriers is 4.5 MHz in System M and 5.5 MHz in System B/G) Then the modulated IF signals are added either at the output of the vision modulator or at the output of the vestigial sideband stage. In both cases, the added signals are low level signals and no special combining circuitry is required. Frequency conversion and amplification is common. So a frequency converter (or a mixer) and a series of amplifiers for aural signal as well as an output combiner are spared, which reduce the cost of the transmitter and electricity consumption of the amplifiers considerably. Although a notch filter to suppress the intermodulation products is used at the output of the intercarrier transmitter, the cost of the notch filter is not comparable to the cost of extra amplifiers and the output combiner. (See the subsection Intermodulation products below)

Intercarrier as used in receiver sets

In TV receivers, the received radio frequency signal is converted to IF in tuner and then demodulated. The output of the demodulator consists of a VF and an aural signal which is in fact an FM subcarrier modulated by AF. (The subcarrier is 5.5 MHz in system B and 4.5 MHz in system M.) The aural signal and the VF are separated by a simple filter. The only extra stage needed for AF (other than the loudspeaker) is an FM demodulator. The intercarrier receiver system makes for easier tuning of a TV station. The viewer could fine tune such a set to get the best picture reception, and not lose sound reception. (Although AF VF signals are combined in the IF stages of the transmitters, they are separated in baseband stages of the receivers.)

Intermodulation products and notch filters

When VF and the aural signal modulate the same carrier the inevitable non-linearity of the electronic circuits cause unwanted signals which are called intermodulation products. The unwanted signals appear on RF spectrum at regular intervals, the interval being equal to the frequency difference of the visual and aural carriers. In TV broadcasting the intermodulation products of the aural subcarrier and the main carrier appear out of the RF band of the TV channel. However, out of band product means an unwanted transmission in the neighbour TV channels. For example, intermodulation products of channel 7 appear in channel 5,6, 8 and 9. That is why notch filters are used in intercarrier system.

References

Worked examples

Example 1 — a first encounter with Intercarrier method

Start with the simplest possible case. Write down what Intercarrier method 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 Intercarrier method 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 Intercarrier method 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 Intercarrier method

In research: Intercarrier method 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 Intercarrier method 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: Intercarrier method is common in secondary-school and first-year university syllabi. It links to neighbouring topics Broadcast engineering, Broadcast transmitters, Television technology, so understanding it makes those chapters shorter.
In everyday life: Look for Intercarrier method 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 Intercarrier method in 20 minutes

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

Frequently asked questions

What is Intercarrier method in simple terms?

Why does Intercarrier method 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 Intercarrier method?

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 Intercarrier method.