Ferrite Beads

[speakerman1]

Do you guys use them? Do you know what they are? Was reading this AM. Will look for it again. Makes very good since. kept wanting to type choke yesterday while talking about RF signals. If I remember right you tune an antenna by using a choke. The longer the antenna the lower the freq. I believe. There is circuitry that can make the antenna think it is longer though. I think. If I am wrong step in and let me know.

larry

 

[laatsch55]

Anything above 20Khz is out of my paygrade.

 

[Gepetto]

Yes use them all the time Larry. Primary usage is on power supply filtering, they work somewhat similar to a choke or inductor but are resistive in their energy absorption and dissipation characteristics. A small wire through the center coupled with a downstream ceramic type bypass cap effectively blocks high frequency noise from propagating through this network. The wire present almost nil DC loss, unlike RC filters that create DC voltage loss dependent on current that is flowing.
Most common usage is power supply filtering for high speed PLL type integrated circuits.

What do you intend to use them for?

 

[speakerman1]

What I read about today was on the ICs. To block out the RF that they pick up. If I read right. Treating the ICs as an antenna. I think that is what I read. Read alot today so I may be confused. Wouldn't be a first time.

Larry

 

[Gepetto]

They are often used on AC power cords to block conducted and radiated EMI that comes out of equipment with switching power supplies in order to conform to FCC and CE requirements. You no doubt have some on the power cords for your computer equipment. They act like an inductor when put around the cable diameter. The frequencies typically are over 10MHz where the beads are most effective, certainly way above any audio frequencies.

 

[rtp_burnsville]

Larry,

We use them sprinkled on all of our circuit boards for the reasons mentioned above. We also use them on I/O ports which contain clocks or fast edge rate logic switching.

Robert

 

[speakerman1]

I'm trying to get this right in my head. I do understand what you guys are saying. When I was reading they said they could be tuned. I'm not up to that point yet in my thinking. When we tuned antennas we used what was called a choke. It wasn't a transformer. It was about the size if a golf ball. We placed it a certain length on the antenna to keep it from going out of the freq. range it was designed for or what the radio was designed for. We could move it when we tested the antenna to get it in a specific range.

Some antennas we used were full wave. What I was reading yesterday was and I agree with this. Is that any conductor can be an antenna. Thus picking up RF. I'm glad Johnny said EMF. I thought I was losing my mind when it kept coming up in my thinking. I didn't realize that that ferrite beads were iron ferrite. Till I read it. OK as I read. This was my thought process. If you use the ferrite on ICs. The RFs will be stopped at the ferrite beads due to the iron content. Am I correct on that assumption? If not please enlighten me.

Larry

 

[speakerman1]

This is where I got my info.

http://audiosystemsgroup.com/Ferrites-Ham.pdf

Larry