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I am using a ferrite core to remove video noise in an NTSC video system. I am using the ferrite core on the video and video GND lines.

I am merely winding the video and video GND lines on the ferrite core. The core used is - this.

The impedance charachteristics is as shown below -

Impedance curve

Now, analog video consists of a base-band signal of approx 5Mhz. I was connecting 2 different video sources to the same connector on my board. The video signals come to the connector as shown below -

Video conn.

Now, I kept observing a lot of roll noise on both my video signals. Now,I coiled the 2 video lines (and their respective GNDs) over 2 independent ferrite cores. This absolutely removed the roll noise and made the video very clean. I gave about 8 turns on the torroid. How did that happen ? How does a ferrite core work ?

Also, can I acheive the same impedance charachteristics using passives ?

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    \$\begingroup\$ That means you hace common mode interference. Check your star grounding of the system. A choke IS a passive element. \$\endgroup\$ – winny Dec 26 '16 at 7:55
  • \$\begingroup\$ @winny. Thank you for the reply. Can I acheive the same with inductors and caps ? \$\endgroup\$ – Board-Man Dec 26 '16 at 11:56
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    \$\begingroup\$ Your common mode choke IS an inductor. Why do you want to get rid of it? \$\endgroup\$ – winny Dec 26 '16 at 12:50
  • \$\begingroup\$ @winny , the physical dimensions of the choke is killing me. I wanted to achieve the same in small packages. \$\endgroup\$ – Board-Man Dec 26 '16 at 12:55
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    \$\begingroup\$ No problem. Get a thinner wire and smaller core or get yourself a very small PCB mounted common mode choke. Also, how do you ground your entire setup? \$\endgroup\$ – winny Dec 26 '16 at 13:00

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