Low Pass Filter for Lab Wiring

Call around local radio stations until you get your hands on a station engineer, and ask them what they do and/or use.

You may get different answers from an AM station than an FM, so think about what frequency of RF you're concerned about.

Consider, also, that the Best Damn Filter in the Universe, applied at the breaker box or plug, won't keep the line cords from picking up common- mode RF and bringing it into your boxes.

--
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My conservative friends think I'm a liberal kook.
Why am I not happy that they have found common ground?

Tim Wescott, Communications, Control, Circuits & Software
http://www.wescottdesign.com

And it may not help at all. I was once plagued by an FM station at

100.1MHz resonating the steel studs in an office building ;-) ...Jim Thompson

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| James E.Thompson, CTO                            |    mens     |
| Analog Innovations, Inc.                         |     et      |
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I love to cook with wine.     Sometimes I even put it in the food.

Thanks but, I am really only concerned about EMI that is already contaminating the 110V wall socket circuit, not what may be picked up through induction.

Just neeed a black box to plug into any socket, that will shunt this to ground. IOW it would clean the entire circuit.

Kevin Walters

I used to pickup our local AM radio station (1430) on my scope when I cranked up the gain. Not only could I hear Rush's voice, I could see it too! Mikek

Corcom, and quite a few other companies make powerline-filter modules, which are intended to be wired between the line and the load. They typically seem to consist of several stages e.g. a hot-to-neutral cap and differential-mode inductive filter, followed by hot-to-ground and neutral-to-ground caps to help take out common-mode noise.

Filters of this sort can be wired into equipment, wired into the mains, or installed in a box which you plug into a wall outlet and which provides a filtered outlet for your equipment.

They're designed primarily for filtering out RFI, and their filtering efficiency drops off fairly sharply below 1 MHz or so. Some types designed for switching-power-supply use (e.g the Corcom EP/VP series) do have some amount of useful noise attenuation down to 20 kHz or so, but it's definitely less than at RF.

Filtering out noise below 1 kHz is going to be difficult (read, "big expensive components with nontrivial electrical losses", I think).

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It sounds like you need a shielded room, with the proper power line filtering. All of your test equipment should already have line filters and if they can't handle the job, it's time to reduce the overall RF levels.

--
You can't have a sense of humor, if you have no sense.

Triplite ISObars work well. Try one of those first. They have cascaded filters for each duplex pair.

Cheers

Delta CA302R will cover the whole 120/240V, how perfectly I can't say (it's a capacitor, basically) but it is a "whole system" device. Wires in at the breaker box (or you can be paranoid/cautious and put one there, and another closer to the point of use). Toss an LA302R on there for the big stuff, too, if you like, or just to be complete. The CA302R (website info is kinda sparse) has a label on it that lists it as a Facility EMI Filter or words to that effect, even though it's billed as a "surge capacitor" for most sales purposes. A capacitor is a capacitor, for both purposes....

Just a customer (I have a set (LA+CA) on both ends of my well circuit, and another on my other panel - seemed a reasonable investment .vs. the price of a well pump, and .vs. lots of little surge protectors - or in addition to / before, depending.)

Shop around. You can do better than the prices listed here:

I think Galesburg Electric was the best deal with shipping the last time I bought any. May or may not still be true (or depend how many you are buying - I think the first pound is kinda expensive at Galesburg since they only do UPS.)

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Cats, coffee, chocolate...vices to live by
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I think the idea sucks. If it's going to work, it needs to be upstream. You want to pass downstream. Adding noise to ground must be at a good point. On a dedicated outlet use an isolation transformer with secondary tied to ground, the first measure of reducing noise.

Greg

We use a LRE-2030 for our shielded room. 150KHz to 18GHz.

I did some googling in the last month as I have the same problem: qrm over mains lines makes almost impossible operating a radio receiver at home, save for multi kilowatts local FM stations. HF is unusable.

Here are a couple pages worth looking at.

I'll probably make one identical to the silicon chip one, except I'll rewire the toroids differently in order to take into account both differential and common mode junk.