Ethernet extension cables do not inherently reduce speed, as long as they meet the following conditions:

1. Cable Category: The extension cable should match the category of your existing cable (e.g., Cat5e, Cat6, Cat7). Each category supports specific speeds and bandwidth. For example, a Cat6 cable supports up to 1 Gbps over a distance of 100 meters (328 feet). If you extend a Cat6 cable with a Cat5 cable, you’ll be limited to the performance of the Cat5.

2. Total Length: Ethernet cables have a maximum effective length of about 100 meters (328 feet). If the combined length of the original cable and the extension exceeds this, signal degradation can occur, which may reduce speed or cause packet loss.

3. Quality of the Extension: A poor-quality extension cable or Ethernet coupler could introduce signal interference or loss. Make sure to use a high-quality extension that matches the original cable’s category and quality.

If these factors are considered, you should experience no noticeable reduction in speed when using an Ethernet extension cable.