If I use this ferrite bead for a USB cable, what can be said about the noise attenuation for 1 MHz and 10 MHz.

The plot only shows the impedance versus frequency, whereas I would like to see the attenuation roughly for a USB cable's interference. I would like to see how much a 1 MHz and 10 MHz interference would attenuate.

Noise originating from the PC and through USB Hub goes into the System. This happens when a nearby device next to PC is activated like motor. All I want to suppress and try if I can attenuate the noise coming through earth or mains through USB cable first.

enter image description here

  • 3
    \$\begingroup\$ Attenuation is dependent on source and load impedance. So you would want to know these impedances in USB transmission. \$\endgroup\$ – Stefan Wyss Dec 12 '18 at 11:08
  • \$\begingroup\$ I see but how can i know that? I there a typical value for USB port input impedance? \$\endgroup\$ – Genzo Dec 12 '18 at 11:09
  • \$\begingroup\$ You need to show how it is being used - try adding a schematic and show where the noise source is and what circuit nodes you want attenuated. \$\endgroup\$ – Andy aka Dec 12 '18 at 11:09
  • \$\begingroup\$ @Andyaka It is used from a PC USB port to a USB Hub's port \$\endgroup\$ – Genzo Dec 12 '18 at 11:10
  • 1
    \$\begingroup\$ Nothing you try basically makes sense until you find the silver bullet. After that it starts to make sense. Be random; try things that don't make sense. No need to worry if they don't make sense just try them and keep trying things additively until you hit the spot. Then remove stuff that you tried until it goes belly-up again. That's the only way I know how to fix these problems generally. \$\endgroup\$ – Andy aka Dec 12 '18 at 12:17

All filters are voltage dividers, like this


simulate this circuit – Schematic created using CircuitLab

  • \$\begingroup\$ In summary, I think you can say this: until current flows through a ferrite bead, you can't know its attenuation. If R2 is infinite, R1 doesn't attenuate. \$\endgroup\$ – glen_geek Dec 12 '18 at 16:45
  • \$\begingroup\$ But dont you guys have any idea what can R2 be roughly if it is a USB port? \$\endgroup\$ – Genzo Dec 12 '18 at 16:51
  • \$\begingroup\$ @analogsytemsrf I like this kind of circuit involved precise explanations thanx \$\endgroup\$ – Genzo Dec 12 '18 at 16:52
  • \$\begingroup\$ What will R2 be (what is the impedance) if that impedance is the input to a USB hub? Suppose you want 12,000,000 bit rate? You'll need about 20 nanosecond time constant. Suppose you need 100 ohms to terminate the USB line. The USB line needs to look resistive up to about 100MHz to minimize reflections. Thus you can insert 100 ohms into R2. What if your USB is much faster? Then the USB line still needs to look resistive, but to much faster data rates. \$\endgroup\$ – analogsystemsrf Dec 13 '18 at 14:19

I've used something similar to get 'hash' off a usb line. I will sometimes loop the cable through a few times. (more turns) I think of this as a common mode choke. But a lot depends on where the noise/hash comes from.


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.