Why a DC (direct current) component is undesirable?

In summary, the author is saying that it is undesirable to have a DC component in a communication signal, because it can cause problems with the transformer.
  • #1
janu203
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When choosing Line Codes (e.g. Bipolar or Polar formats) for transmission of bits over a communication channel such as twisted pairs, it is always desirable that no DC component is present for a particular choice.
According to William Stallings (Digital Communication Book)
"With a dc component to the signal, there must be direct physical attachment of transmission components.
With no dc component, ac coupling via transformer is possible; this provides excellent electrical isolation, reducing interference"

I cannot understand what does he mean in above paragraph. I don't know much about AC/DC circuits and their workings
 
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  • #2
janu203 said:
When choosing Line Codes (e.g. Bipolar or Polar formats) for transmission of bits over a communication channel such as twisted pairs, it is always desirable that no DC component is present for a particular choice.
According to William Stallings (Digital Communication Book)
"With a dc component to the signal, there must be direct physical attachment of transmission components.
With no dc component, ac coupling via transformer is possible; this provides excellent electrical isolation, reducing interference"

I cannot understand what does he mean in above paragraph. I don't know much about AC/DC circuits and their workings
A DC component is undesirable for transformer-coupled communications, because it can cause saturation issues in the transformer cores. You would rather use all of the B-H curve of the transformer for coupling the AC communication information, and not have an offset B-H curve start to limit the AC components.

You want to use as small a transformer as you can for cost reasons, but as you make it smaller, the AC component of the communication signal starts to get close to the tips of the B-H curve. Adding a DC component to the waveform just pushes you that much farther toward one of the tips of the B-H curve, which is bad. In other words, to accommodate a DC component, you have to make the transformer physically bigger than you would like, which makes it more expensive.

Does that help?
 
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1. Why is a DC component undesirable in electrical systems?

A DC component is undesirable because it can cause problems such as electrolysis, which can damage components and lead to system malfunctions. It can also cause interference with other electronic devices and reduce the efficiency of the system.

2. How does a DC component affect electrical equipment?

A DC component can cause overheating in electrical equipment, leading to reduced lifespan and potential failures. It can also cause damage to sensitive components and disrupt the overall functioning of the system.

3. Can a DC component be eliminated from an electrical system?

While it is not always possible to completely eliminate a DC component, measures such as using capacitors and transformers can help reduce its effects and keep it within acceptable limits.

4. What are some common sources of DC components in electrical systems?

DC components can be introduced into electrical systems through sources such as unbalanced loads, rectifiers, electronic devices, and power supply issues. It is important to identify and address these sources to minimize the presence of DC components.

5. How does a DC component affect power quality?

A DC component can lead to poor power quality, which can result in issues such as voltage fluctuations, harmonic distortions, and power factor problems. This can impact the performance and reliability of electrical systems and cause damage to connected equipment.

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