micma18:
USB.org's FAQ snakker om "propagation", altså udbredelse, og at det er det der forhindrer så lange kabler. De nævner intet om at impedans og/eller kapacitet i kablerne har nogen indflydelse.
Det er altså ikke på grund af spændingstab eller "misdannede" pulser at signalet forsvinder...
Q2: Why can't I use a cable longer than 3 or 5m?
A2: USB's electrical design doesn't allow it. When USB was designed, a decision was made to handle the propagation of electromagnetic fields on USB data lines in a way that limited the maximum length of a USB cable to something in the range of 4m. This method has a number of advantages and, since USB is intended for a desktop environment, the range limitations were deemed acceptable. If you're familiar with transmission line theory and want more detail on this topic, take a look at the USB signals section of the developers FAQ.
2. I want to build a cable longer than 5 meters, why won't this work?
A: Even if you violated the spec, it literally wouldn't get you very far. Assuming worst-case delay times, a full speed device at the bottom of 5 hubs and cables has a timeout margin of 280ps. Reducing this margin to 0ps would only give you an extra 5cm, which is hardly worth the trouble.
DragonOne:
Prøv som de siger i den FAQ at sætte flere USB hubs op, så hvert kabel mellem dem kun er 3-5 meter. Det er en grim metode, men det er altså heller ikke formålet med USB, det her...
Jeg ville dog selv foreslå remote control med VNC eller lignende.