Cable Passing Through Metal: What Is It?

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The cylindrical container near the USB connection on the camera is identified as a ferrite choke, which helps eliminate high-frequency electromagnetic noise from the cable. This choke works by presenting high common-mode impedance to RF signals, effectively acting as a barrier to reduce radiated electromagnetic interference (EMI). While it is common to find these chokes in various devices, their placement is not critical for EMI reduction, as the "break" in the line can be effective at different points. The discussion highlights that while ferrite chokes may not always be necessary, they can improve signal integrity in certain situations. Understanding the function of these components can aid in grasping basic electrical engineering concepts related to noise reduction.
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Hi,
My camera USB cable has this cylindrical container close to the end where the USB connects to the camera. When I opened it up, the cable was going through two holes in the metal. The metal wasn't perfectly black, and it wasn't smooth.
What is that piece of metal for? I don't know much about electrical engineering.
Thanks.
 
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It's a ferrite choke, to kill high-frequency electromagnetic noise on the line. Arguably, they don't do much under normal circumstances.

- Warren
 
Thanks. I notice the same thing in other devices as well. Why isn't there one at the end close to the computer?
 
The choke presents a high common-mode impedance to any RF signals on the cable, so it effectively looks like a break in the line for RF common mode signals. RF common mode signals are what cause radiated electromagnetic interference (EMI), which shows up as noise on broadcast TV receivers and radio receivers. It usually doesn't matter where the "break" is placed in the line for EMI purposes (but not always).
 

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