[amblin]

You know, those little clamp things on many cables such as USB , LAN,hdmi and power cord. That the kids usually develop a special interest once figured how to open them.. 

Like these :  http://datasheet.octopart.com/ZCAT3035-1330-TDK-datasheet-8884035.pdf

According to the above datasheet, they're quite useful : a ferrite core increases the cable impedance at high frequencies thus filtering out some HF noise while apparently NOT affecting the impedance in the audible range and will not affect the AC frequency.

My question is.. IF they're so useful,simple and cheap (30 - 50 cents each), why hi-end cable/ interconnect  makers never use them? Not even on digital and AC cables?

Thanks.

[brucek]

My question is.. IF they're so useful,simple and cheap (30 - 50 cents each), why hi-end cable/ interconnect  makers never use them? Not even on digital and AC cables?

Thanks.

The assumption is that every input circuit that cables are connected to already enjoy a low pass filter that removes any high frequency noise.

brucek

[Speedskater]

Ferrites are very effective at blocking interference riding on cables of all types.  But it's somewhat tricky selecting the correct setup depending on the interference in question.

Jim Brown is both Audio Engineering Society past committee chair on EMI/RFI interference and a Ham radio operator. Don't let the title of this paper fool you, much also applies to audio systems.

"A Ham's Guide to RFI, Ferrites, Baluns, and Audio Interfacing"

by Jim Brown K9YC
Audio Systems Group, Inc.
http://audiosystemsgroup.com

The basis of this tutorial is a combination of my engineering education, 55 years in ham radio, my
work as vice-chair of the AES Standards Committee working group on EMC, and extensive research
on RFI in the pro audio world where I’ve made my living.

http://www.audiosystemsgroup.com/RFI-Ham.pdf

****************************************

Many more Jim Brown papers.

http://www.audiosystemsgroup.com/publish.htm

[amblin]

Thanks for the info, that's a very good read, took me 3 days to digest just the fundamentals and now I'm curious about ham radio...

[Speedskater]

A US west coast Ham group sometimes buys ferrite cores in lots of 1000.

But each core model has a limited interference frequency range.  Hams have a great advantage when it comes to fighting interference (but hen Hams have much bigger interference problems) they have radio receivers that can measure the interference frequency and strength.  So they can see if their filter is effective.