Why does a USB4 cable become unstable when it gets longer?

Why does a USB4 cable become unstable when it gets longer?

Many customers think a USB-C cable is just a little longer, so it should not make a big difference. But for USB4 40Gbps high-speed transmission, cable length is a critical factor.
The higher the data rate, the higher the signal frequency. And the higher the frequency, the more sensitive the signal becomes to cable structure, conductor design, shielding, impedance control, connector quality, and overall signal integrity.

One key parameter is Insertion Loss.
Simply put, this means the signal becomes weaker as it travels through the cable. The longer the cable, the higher the loss, and the weaker the signal received by the device.

Another important parameter is Return Loss.
Return Loss is related to signal reflection. If the cable impedance is not well controlled, or if the connector structure is not stable enough, part of the signal may reflect back and affect high-speed transmission quality.
Engineers often use an Eye Diagram to evaluate whether the high-speed signal is stable. A clear eye opening usually means better signal quality. If the eye becomes narrow, messy, or distorted, it may indicate that the signal is affected by loss, reflection, noise, or interference.

That is why the USB4 cable length limit matters.

For short-distance use, a high-quality passive USB-C cable may work well. But if the cable needs to be longer while still maintaining 40G transmission, an Active USB-C cable may be required. Active cables may include a Retimer or signal enhancement chip to clean up and strengthen the signal, helping maintain stable transmission over longer distances.

For customers using external SSDs, docking stations, professional displays, workstations, test equipment, medical imaging systems, industrial devices, or other high-speed connectivity applications, the cable is not just a simple accessory. It directly affects system stability.

STAR FIRE TECH provides various USB-C and USB4 cable solutions for high-speed data transfer, charging, video output, and professional connectivity applications.

Stable signal. Fast data. Reliable connection.

📌 Learn more:
www.starfirecableshubs.com
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