RFI/EMI Issues

[Keith Moore]

I have had an RFI/EMI issue some years ago. I ended up lining the inside of my live room with copper screen and grounding it. This reduced the noise to a very usable level. Recently it appears to have gotten worse and I would like to try to trace the heart of the problem. Below I have attached an audio sample of this noise interference.

To suss out some suggestions I have shut off the main breaker in the house and the noise is still present using a guitar and a battery powered amp. I also took the guitar outside and walked over to a field across the street where the sound lowers significantly. I added 2 grounding rods to the earth connected in series and attached to the copper screen. I also added 2 grounding rods attached in series and attached them to the service panel. I will be trying Ferrite Chokes later today but as I said before I am looking for advise on how to trace down the source. I've read about using a battery powered AM radio, where can you acquire one and what exactly do you do with it?

Any other suggestions are welcome.

RFI/EMI Sample: http://dl.dropbox.com/u/8032276/RF.wav

Thanks,

Keith Moore

[Fletcher]

You should see how many holes you have in the copper shield... you should only have one [and that should be by or under the door... which should also have copper screening that mates with the screening in the rest of the room when the door is shut].

What you're essentially building is a Gaussian sphere which will take any airborne electricity [RFI - EMI] and drain it to ground. You want one ground stake [not two] and one path to ground. If you have a window in the control room you need to figure out a way to include that in the sphere. In the past I've done it by running other light copper wires through it forming like 1/2" cubes that were between laminated layers of glass and then soldering those wires to the screening on the rest of the room.

Its not for the faint of pocket book... but it works like a charm if its done right. As an added bonus - there is abso-fvckin-lutely zero "cell service" inside one so you never have to tell a client to shut off their cell phone -- the room does it for you!!

Peace

[John Willett]

Originally Posted by Fletcher

As an added bonus - there is abso-fvckin-lutely zero "cell service" inside one so you never have to tell a client to shut off their cell phone -- the room does it for you!!

Surely there is even more reason to shut off a cell phone.

A phone inside a Faraday Cage will ramp up more and more trying to contact the cell it can't reach and cause even more interference!

[Keith Moore]

Hey Fletcher,

When I first tackled this issue I has a fully surrounding cage which made a HUGE difference. I decided to get cocky and redesign the live room some years ago, I disassembled the cage and only lined the walls connecting it to the ground of a single outlet receptacle. I didn't notice a significant increase in interference at the time and for years after. But now it seems to have increased. I "could" get more copper screen and just go nutty. But before coming to that I wanted to attempt to do some ghost hunting and see I'd I can locate and hopefully find an issue that can be fixed rather than hissing from it under copper blankets. Do you have any insight on efforts of tracing down such anomalies?

Originally Posted by Fletcher

You should see how many holes you have in the copper shield... you should only have one [and that should be by or under the door... which should also have copper screening that mates with the screening in the rest of the room when the door is shut].

What you're essentially building is a Gaussian sphere which will take any airborne electricity [RFI - EMI] and drain it to ground. You want one ground stake [not two] and one path to ground. If you have a window in the control room you need to figure out a way to include that in the sphere. In the past I've done it by running other light copper wires through it forming like 1/2" cubes that were between laminated layers of glass and then soldering those wires to the screening on the rest of the room.

Its not for the faint of pocket book... but it works like a charm if its done right. As an added bonus - there is abso-fvckin-lutely zero "cell service" inside one so you never have to tell a client to shut off their cell phone -- the room does it for you!!

Peace

[Keith Moore]

Any other suggestions for EMI/RFI source hunting?

[edva]

Originally Posted by Keith Moore

Any other suggestions for EMI/RFI source hunting?

I always seem to find it with a hot single-coil guitar pick-up, as you said you were doing.

[Keith Moore]

Originally Posted by edva

I always seem to find it with a hot single-coil guitar pick-up, as you said you were doing.

And what did you end up discovering as the source of your problem? And how did you go about solving it?

[baskervils]

Originally Posted by edva

I always seem to find it with a hot single-coil guitar pick-up, as you said you were doing.

Same issue recently. It was the single coil pickup in the guitar, which I replaced.

[thronechild]

I am having similar issues with bass and guitar instruments and while researching came across a conductive paint:

Electromagnetic Field Shielding Paints

Anyone ever used or heard of this?

Also Maybe this is the type of tool you are looking for, haven't tried it just came across the info while researching.

Emf or gauss meter

[Keith Moore]

So I found some time the other day to do further testing on this issue. I plugged in a single coil pickup'd guitar (as they seem to pickup interference the most) to a battery powered amp. I first disconnected the lighting rod that goes to an old antenna on top of the house. That proved to do nothing. Since it was nice outside I took a stroll around the house. When I entered the garage it was almost completely gone. So I proceeded to walk around the house itself where I found myself a set of wires that come in from the street and travel down the side of the house. When standing in front of this wires with the guitar the interference screams louder than I've ever heard it before. This wires turned out to be for the Cable TV.

I did not have the time to screw around with this as I was heading home at the moment but I had a close look at it with my brother who seems to believe that the ground connection from the street is not connected anywhere. The ground where the street line splits into the coax line into the house has a wire which I still need to trace.

I know calling the cable company "should" be the first thing I do but I figured I'd reply to this thread and see what you guys think. Should I just ground this line into the ground with an 8' grounding rod myself? Or call the cable guy who will most likely look at me like the idiot I am walking around the streets at 3am with a guitar and pocket amp

[audiotech]

It sounds to me that CATV has a nasty leak in their line. It could be their actual cable, a splitter or even the connectors on the cable. If you need an AM battery powered radio, you can probably get them at Radio Shack cheaply. AM radios will pick-up just about any type of noise generated in the environment. Depending on the antenna, sometimes you can locate the troublesome noise just like directional finding equipment by just turning the radio in the direction of the noise until the noise nulls or gets louder.

It's always better to eliminate the noise rather than to suppress it, if you can.

Dennis

[Syncamorea]

Originally Posted by Keith Moore

I know calling the cable company "should" be the first thing I do but I figured I'd reply to this thread and see what you guys think. Should I just ground this line into the ground with an 8' grounding rod myself? Or call the cable guy who will most likely look at me like the idiot I am walking around the streets at 3am with a guitar and pocket amp

Wow, deja vu. When we moved into our current home in '04, we had the same problem and it peaked each day around dinner time. Turns out most of it was coming in on the TV cable also. I called the provider and asked for them to send their best tech out. He did a great job, initially reducing the noise level in my DAW mix buss out by 6dB by just installing a new piece of cable that connected their distribution box to the house. I got studio grade coax at Lowe's that claimed to have 90dB of isolation whereas the cable company's stock cable is spec'ed at -45dB. The cable guy went around and cleaned & greased all of the connections and put in a new main splitter in. I then went through the basement with a fine toothed comb, replacing all of the old cable I could get to, removed two useless splitters, etc. I routed the new cable away from A/C - the original stuff was right on top of the A/C line that fed the microwave and oven, which was probably contributing to the peak noise issue at dinner time.

I have since fought the battle to chase down and replace the cable up to the 2nd floor - what a pain in the ass! The noise is still detectable but is down 10 to 12dB compared to where it was at when we moved in. It may be worth your time to reorient your gear a little to see if you get noise reduction. Sometimes angling a transformer a few degrees makes a significant difference. I also put in a separate ground rod outside for the cable and that brought audible reduction in the noise in the 1K to 2.5kHz range. Having all gear plugged into good quality A/C line filters brought another 2-3dB of noise reduction and that only cost ~$2K.

[Syncamorea]

Originally Posted by Fletcher

What you're essentially building is a Gaussian sphere which will take any airborne electricity [RFI - EMI] and drain it to ground. You want one ground stake [not two] and one path to ground. If you have a window in the control room you need to figure out a way to include that in the sphere. In the past I've done it by running other light copper wires through it forming like 1/2" cubes that were between laminated layers of glass and then soldering those wires to the screening on the rest of the room.

That's the hardcore approach, but it is the correct approach. I helped to design and build an instrumental analysis laboratory and managed to get the lab chief to fork over for a Farady cage. Mind you, the lab had a footprint of over 30K square feet and a height of 30', so there was a over ton of copper mesh involved. When we got down to checking for leaks, I made a coil of copper wire and ran it into a spectrum analyzer and a high gain audio amp with a cheap little speaker attached. We were like Sherlock Holmes, looking for clues.

Every single instrument we installed in the lab operated beyond manufacturer specs, typically generating resolution and sensitivity numbers better than the manufacturers had seen at any installation. Part of that performance advantage was due to the vibration isolation that we designed in (30 foot pilings 3' in diameter supporting the slab with high tech polymeric dampening between the pilings and the slab. I found out about that polymer by talking to a recording studio builder.

BTW, Fletcher, I assume you know that RFI isn't actually airborne electricity. I try to keep lightning out of the studio whenever possible, unless it relates to performance energy. I should rename my place Plasma Studios!

[Fletcher]

Originally Posted by Syncamorea

Fletcher, I assume you know that RFI isn't actually airborne electricity.

That would be an incorrect assumption... I frankly never gave it much thought [suppose I should have] - but now that you brought it up... any suggestions on where I can look so I can learn more about it?

[Speedskater]

Just some random thoughts:
a] For others planning on screening a room. One expert suggested using steel screen material rather than copper. As being lossy might be a good thing.
b] Connecting to Mother Earth might increase interference. (see link)
c] If you connect the screening to the electrical ground (PE, EGC) do it at the Service Entrance rather than at a room outlet box.
e] Jim Brown being both the AES committee chair on EMI/RFI interference and a HAM (Amateur Radio Operator) has several papers on interference.

Audio Systems Group, Inc. Publications

[Speedskater]

I would say that some RFI is airborne and some is wire-borne.

[Syncamorea]

Originally Posted by Fletcher

That would be an incorrect assumption... I frankly never gave it much thought [suppose I should have] - but now that you brought it up... any suggestions on where I can look so I can learn more about it?

Wikipedia's pages aren't too bad.

Electromagnetic radiation - Wikipedia, the free encyclopedia

Electromagnetic interference - Wikipedia, the free encyclopedia

Whereas "airborne electricity" would be some kind of discharge like an electrical arc:

Electric discharge - Wikipedia, the free encyclopedia

I can't believe how much I'm referencing Wikipedia these days but alot of the university sites I used to use have been poorly maintained. May as well look at the Wiki for plasma physics too, just to see the cool picture!

http://en.wikipedia.org/wiki/Plasma_(physics)

[kafka]

Been there, done that, wrote a big thread on GroupDiy on it: Extreme EMI. I shut the main breaker off and still had horrible hum. The issue turned out to be a broken neutral to the houses downstream from mine. All return current was going through the water main, through my house, and across my good neutral to the transformer. I measured 12 amps and more at times. Aside from the hum, this was an astronmically dangerous condition. It's a wonder nobody was electrocuted over the years.

The good news was that the power company took it seriously and replaced all of the power to my block. My neighbor's power improved dramatically as a result as well. I was fortunate because it was the power company's issue. However, it could just as easily have been caused by a loose or disconnected neutral inside one of my neighbor's houses, which would have left it to them to solve. The neighbors thought I was an absolute nut until the power company came out and dug up our lawns, and all of their electrical problems (i.e. TV interference, dimming lights, etc) went away.

Pick up a handheld EMF meter to try to track down the source. It's easier than lugging around a guitar. Mine is similar to this: Amazon.com: Lutron 822-A Fully Digital EMF Meter (Wide Range, High Resolution): Home Improvement

Also look for a copy of Edward Leeper's Silencing the Fields. It's a very accessible book on the subject. Unfortunately, it's also out-of-print.

As far as room-sized shielding goes, absolutely forget about it. It's not practically possible under any circumstances. The only solution is to balance your power. i.e. if a conductor carries current, there has to be another conductor right next to it that carries an opposite current, which will nearly cancel out the magnetic field.

[Keith Moore]

Hey guys, thanks so much for all your replies. I have just gave my cable guy a $20 hand shake as he just solved my issue. Turns out there was an analog signal booster in the mix plus a ton of old "59" wire which is poorly shielded. After swapping some wires around and removing the last "59" wire from the chain the interfering frequency dropped about 90%.