1. What Is Velocity Factor in Cables?

Definition: Velocity Factor (VF) is the ratio of the speed of an electromagnetic wave in a cable to the speed of light in a vacuum.

Purpose: It helps determine signal propagation speed in transmission lines and is crucial for timing and phase calculations in RF systems.

2. How Does the Velocity Factor Work?

The velocity factor is calculated using:

Where:

• \( VF \) — Velocity Factor (dimensionless)
• \( c \) — Speed of light in vacuum (299,792,458 m/s)
• \( v \) — Wave velocity in the cable (m/s)

Explanation: The velocity factor indicates how much slower signals travel in the cable compared to light in a vacuum.

3. Importance of Velocity Factor

Details: Knowing the VF is essential for designing transmission lines, calculating electrical lengths, and ensuring proper signal timing in communication systems.

4. Using the Calculator

Tips: Enter the speed of light (default 299,792,458 m/s) and the wave velocity in your cable. Both values must be > 0.

5. Frequently Asked Questions (FAQ)

Q1: What's a typical velocity factor for common cables?
A: RG-58 coax has VF ≈ 0.66, while CAT5 Ethernet cable is about 0.64. Fiber optic cables typically have VF ≈ 0.67.

Q2: Why is the velocity factor less than 1?
A: Signals travel slower in cables than in vacuum due to the dielectric properties of the insulating material.

Q3: How does VF affect antenna design?
A: When using coaxial cable feed lines, the electrical length differs from physical length by the VF, affecting impedance matching.

Q4: Can VF vary with frequency?
A: Yes, some cables exhibit dispersion where VF changes slightly with frequency, especially at higher frequencies.

Q5: Where can I find a cable's velocity factor?
A: The VF is typically specified in the cable's datasheet or technical specifications from the manufacturer.