ARRL Technician Practice Exam

Which of the following is a common reason to use shielded wire?

1. To enhance the appearance of the installation

2. To improve the power transmission

3. To prevent coupling of unwanted signals to or from the wire

4. To increase the weight of the wire for stability

The correct answer is: To prevent coupling of unwanted signals to or from the wire

Using shielded wire is commonly done to prevent the coupling of unwanted signals to or from the wire. Shielded wire has a conductive layer that surrounds the insulation and the inner conductor. This shield serves as a barrier against electromagnetic interference (EMI) from external sources, which can introduce noise and degrade the quality of the signal being transmitted. The effectiveness of the shield in blocking unwanted signals is particularly important in environments with high levels of interference, such as in industrial settings or near other electronic devices. The shielded wire thus helps to maintain the integrity of the signal and ensures reliable communication, making it an essential choice in many applications where data fidelity is crucial. While other options might contain elements of truth in different contexts, they do not capture the primary function of shielded wire, which is to safeguard against interference. For instance, enhancing the appearance of the installation is not a primary function of shielded wire, nor does shielded wire inherently improve power transmission or increase the wire's weight for stability. The core utility lies in the protection against unwanted signal coupling.