It is all about the right tool for the job

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In Reply to: Mmmmmmm... (long) posted by cheap-Jack on December 15, 2006 at 08:39:01:

No, I was talking about common mode noise and a line filter for hot and neutral. In many circumstances the common mode noise on the grounded neutral would be shunted straight to electrical ground and would not go through the neutral winding of the common mode choke. In those cases the common mode choke would not be working as well as it could.
Now it is entirely possible for some common mode noise (imagine very high hertz like 2mhz) to find a lower impedance path to ground through the load and stray coupling. Say a cell phone site was on the top of a sky scraper. The normal electrical ground wiring, being perhaps thousands feet, could have a very high impedance to a 2mhz signal/noise. But due to bonding and lightning protection there might be a lower impedance path to ground through leakage and capacitive coupling for that 2mhz noise. Now the common mode choke can do its best job. So in most cases a pair of differential chokes or an isolation transformer works better for us at home. But they cost a lot more which is why the CM choke and X/Y caps are the norm. But they aren't usually the best tool for the job, especially at home.
A common mode choke can be a good thing to consider on a DC power circuit where a transformer can't be used. JW Miller offers a line of very nice differential mode chokes. Look at the 5524 and the 5520. Despite the DC rating they are UL approved for AC in a commercial surge suppressor. Jon Risch has some good plans for building a filter on his web site. The performance is far better than the commercial common mode choke based line filters.

Russ

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Follow Ups Full Thread

Topic - Bing Dave Cigna - here's a relevant reference for CM choke used as noise filter. - cheap-Jack 09:20:19 12/14/06 (5)

You Win! - Dave Cigna 15:43:19 12/14/06 (1)

Everybody wins. - cheap-Jack 07:41:14 12/15/06 (0)

Much better - Russ57 15:34:13 12/14/06 (2)

Mmmmmmm... (long) - cheap-Jack 08:39:01 12/15/06 (1)

It is all about the right tool for the job - Russ57 10:58:15 12/15/06 (0)

Follow Ups

It is all about the right tool for the job - Russ57 10:58:15 12/15/06 (0)

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