Getting rid of radio freqencies, qick, efficient and easy

K

kikling

New member
No, I'm not going to tell you how to do this, i need someone to tell ME, sorry if the subject sounded kind of misleading. Well Please someone help me out, i'm ony 14, well heres the question:
I have studio, (was formely a garage) that was constructed a year ago. Its 90% sound proof but there are things that suck about it. First is that it was made it not just for me to record and play, but for my sister to dance. So we had to put wooden floors, and a mirror that takes up a whole wall, second, it is perfectly squared in shape and third, i get strong radio frequenicies when my guitar cables are half plugged in and when i'm on the phone. So overall i have a room where sound bounces and Radio Disney is constantly playing. I would like to know if someone knows a simple, cost effecient way to help stop these frequenicies from screwing me up. Oh yah and i dont know if this matters but, my amp is on the west wall of the studio, facing east, located in Sherman Oaks,CA, USA the PLANET EARTH.
Thanks a lot
 
First of all ........ don't leave your guitar cords half plugged in!!!
Second .... ask your parents to sink a new earth line in, a better earth on your power supply will most likely do away with your radio frequency problems. It can be as simple as getting a brass pipe and hitting it into the ground as deep as you can.
 
If the better earth doesn't work you can always build a faraday shield around the room - this involves lining the wall with chicken wire or similar and earthing it.

cheers
John :)
 
No disrespect to the previous suggestions, but forget this room size Faraday shield idea. This is too complicated, too expensive, too immobile, and unless done extremely skillfully, usually results in no reduction in radio frequency interference at all.

1.Make sure you have a good ground.
2.Test your amp by turning the volume to all the way up without anything plugged in. You might hear some mild hiss, but you should not hear any hum or radio stations. If you do, take it in for repair.
3.Now plug your cable into the amp (turn down the volume first!) and make sure the free end is not touching anything (hang it off the edge of a table). Turn the volume up again and listen for the radio. Go buy a high quality cable if you hear anything but hiss. You can test the cable at the music shop in the same manner.
4. If all this is fine but you still get noise from your guitar, take it to a good guitar repair shop and have it shielded. This should include a foil (not conductive paint) lining of the electronics and full aluminum covers over the pickups.

This will cost you far less money and effort than shielding your room, plus it’s portable!
 
barefoot said:
No disrespect to the previous suggestions, but forget this room size Faraday shield idea. This is too complicated, too expensive, too immobile, and unless done extremely skillfully, usually results in no reduction in radio frequency interference at all.
Click to expand...

Too expensive??? See, that's the EXACT mentallity I get so upset over. Do you want to know how much the foil cost us? It was $25, and it covered ALL the walls in MY studio, which is a shit load of square footage. One room would be covered SO easily. And for $25 it's not like you're going to die. And it wouldn't have to be done SO skillfully... Hell, you could not even hook the foil to the ground and it will STILL work. It just works that way. You don't have to know any kind of formula or anything, just know that it works because it has to, it doesn't have a choice.
So, if you're going to choose between options, don't think that a foil faraday cage is expensive. And it's not complicated either. Just slap it up with wall paper paste, which is also in expensive.
 
Expensive:
Maybe not, if you’re going to leave exposed foil on the walls and floors. This doesn’t seem very practical. Kikling has a finished garage. Gutting the inside and refinishing seems like it would be pretty expensive to me.

Complicated:
Here are some good quotes from an AV engineering site I found. http://www.engineeringharmonics.com/papers/s_vc.htm#3

"Whenever a conductive material passes through a shield, for example, when a conductor passes into a metal enclosure, the effectiveness of the shield is greatly diminished. This is simply because any fields impinging on the shield on one side are conducted through the shield on the conductor and re-radiated on the far side of the shield. See Figure 3-2. Even the smallest opening with a conductor through it is a significant shielding problem."

Do you have any wires, metal posts, or such entering your shielded room? They conduct radio signals into the room.

"Any opening in the shield will diminish its effectiveness. The most interesting thing about electromagnetic leakage through slots is that the longest dimension on the opening is critical not the total area of the opening. For example, a ten by 1/10th inch slot will be about 10 times more leaky than a 1 by 1 inch square hole, even though both have the same total area. The general guide line is that slots should be kept shorter than 1/20th of the wavelength of the highest frequency of concern.”

Do you have any gaps in your shielding like windows, door seals or such? They leak like sieves.

Also, the shielding does not save you from any radio generators like computers that are inside the room. Every piece of audio equipment you own should be properly shielded. If they are not, fix them. This simple step makes a shielded room superfluous.
 
Oh yeah kikling! I remember you! You were the kid who out-recorded your friend some months ago who owned a VS Daw. How ya' doin??!!I have no advice 4 u, but just wanted to say Whassup!!
Peace
Mr.Q
 
Dude Dude Dude... you're making it a bit more complicated than it needs to be.
I agree 100% that unless this guy intends to refinish his surfaces that my idea isn't practical.
But the whole shielding thing doesn't need to be SO complicated. The question you have to ask is, do you want to try protecting against radio waves from the outside, or do you not care? So, you could either ignore it and not do anything, which would leak everything, or at least do a little bit and do what I'm doing. In electronics I work with shielded cable all the time and I see how foil protects from interference. I've run motor power wires through some pretty noisy areas and the motors control perfect and get no cross talk. All I'm doing with my studio is making it as close to that as possible. And about sheilding your equipment... that all comes later, but you have to protect the building before you do that, and you have to do it before you put up the final layers of the walls.
I just wanted to make sure everyone doesn't get scared when thinking about making a faraday shield for their studio. You just have think of these simple things: Ground your sheild from various spots, and make sure to cover as much surface area as possible with the shield.

Later,
-Brian
 
It sounds like he’s talking about stepper motors. These are precision motors like those used in robotics. They rotate incrementally in discreet “steps” or fractions of a rotation. The steps are controlled by electrical pulses. In very high precision applications like computer chip manufacturing equipment, where thousandths of a millimeter can make or break you, these motors are very sensitive to bad connections and cable interference.
 
?? Nope.

barefoot said:
It sounds like he’s talking about stepper motors. These are precision motors like those used in robotics. They rotate incrementally in discreet “steps” or fractions of a rotation. The steps are controlled by electrical pulses. In very high precision applications like computer chip manufacturing equipment, where thousandths of a millimeter can make or break you, these motors are very sensitive to bad connections and cable interference.
Click to expand...

Ahh, no, that's not what I'm talking about. I know what those are, but that's definately not what I'm talking about. What I'm talking about are electric motors for things like exhaust fans, blowers, these kinds of things are all electric motors. When you've got 100 feet of wire that can give off quite a bit of cross talk to nearby wires, up to 60 volts in some cases here. The cable I'm talking about is a 3 conductor cable, 12 AWG, each conductor is shielded and then the entire case has a shield. This eliminates all cross talk. The foil cuts the magnetic lines of flux (caused by the expanding and collapsing electric fields of AC) and the shield, which is just a wire touching the foil, is connected to ground. The lines of flux won't go further than the foil becuase they actually induce a voltage into the foil which is grounded. That's the basis of my studio's shield.
Shields are used for a lot more than precision work, don't automatically assume I'm talking about a stepper motor with 10,000 stopping points.

Later,
-Brian
 
Brain,
Cool, I was just guessing. I usually don’t associate high power applications with interference like that. I’m glad to learn something new every day.

But, I still disagree with you on the efficacy of room shielding.
 
Shielding

One other cheap idea for eliminating radio from your guitar amp (which, as a high gain piece of equipment, seems ultra susceptible), although I've not tried it for other types of inputs:

place a piece of tin foil over the input of your amp, and plug the cable directly through it. It really works! I was in the studio once (a professional studio with very poor shielding) and we were ready to cut, and you could hear the radio in the cans. We tracked it down to my amp, and we did this trick, and voila, no more radio.
 
I'm with barefoot. Shielding a whole room is very difficult to do really well. Don't get me wrong: you can actually get some good out of doing it haphazardly, but doing it well enough to *predictably* make a significant difference in EMI is pretty difficult to do. And cut-and-try gets to be time-consuming...

Several good points have been made. It is very hard to shield apertures like doors and windows, and leaving a slot in the shield tends to create a waveguide and let the cooties come pouring in anyway. However, having said that: you still get some attenuation in some cases, and some may just be enough for youre specific case.

One thing I have to mention, though. Brian said "Hell, you could not even hook the foil to the ground and it will STILL work." This, unfortunately, isn't true in general. It *may* work, but it might actually make matters worse- just as building a good shield with a bad ground bond may actually make matters worse, not better.

If you put a big hunk of something conductive in a strong RF field, and the dimensions of the "something" are just right with respect to the wavelength of the source, you can set up a resonator and make the problem locally *worse*, not better! Think "microwave oven". If you are going to shield things for RF rejection, the *first* priority is to get a good ground bond: and for RF shielding, that means a very low inductance ground bond. Short, fat, straight- use the minimum possible number of bends, and for _sure_ no loops. The bottom line is that RF behavior is a completely different world than our nice, simple, essentially-DC audio stuff, and inductive effects simply cannot be ignored.

I've personally had mixed luck in building adequate Faraday cages for audio, but given that even the best professionals in the field have a hard time achieving adequate results, I don't feel too bad about it. In the late '70s, I was involved with a band that rehearsed in a garage at the base of the WBZ radio/TV broadcast tower in Needham, Ma. What was their ERP back then, maybe 5 megawatts? The back yard fence was literally right against the perimeter fence of the transmitter site, and the RF field strengths were so high that the 8-foot flourescent light tubes in the garage would never go all the way out- they'd always glow just a tad bit, even if you took 'em out of the fixture. I vaguely recall it being on the order of 5-6volts/meter when we measured it! Now, _that_ was an interesting challenge.

We built the shield for that one with tight-mesh aluminum window screen wire, bonded to #8 solid copper that ran directly to ground rods outside the garage walls (6-inch total length from the corners of the room!), and with phosphor-bronze grounding fingers around the periphery of the door so that that aperture would be shielded when the door closed. We also completely shielded the floor under the carpet and bonded it to the wall runs, since you need to make the cage _complete_ if you expect good results. I put in some heavy-hitter Webcor EMI filters on the power feed, since an unbelieveable wad of hash could get in that way. After some more hackery, we also bonded the chain link fence in the back yard to ground at 4 points, because I got the inkling that it was reradiating some harmonics at us (maybe the corona discharge visible at the gate latch on cold, clear nights told me that). We got to the point of being able to tolerate the EMI, but never killed it anywhere near completely. At least the lights would go out all the way after we were done!

Doing this sort of work can be a crapshoot, unless it is really carefully designed. You absolutely can get satisfactory results with just aluminum foil, a staple gun, and good intentions. The problem is that you can also get no benefit at all, or even make it worse. RF is gnarly stuff, dude, and it can be a hard beast to tame.

For the original poster: IMNSHO, the very first place to start is with a good, low inductance, single point ground for the rig. Setting up a clean, solid star grounding arrangement is good enough to tame probably 75% of the EMI problems commonly encountered in the field. If that doesn't do it, _then_ you can pull out the bigger hammer.

Jeez- I'm a junior member now, not a newbie any more. Whee!
 
skippy,
That’s a pretty amazing situation! At those signal strengths there might have been significant ground penetration. Your ground rods could have even been floating on WBZ! You might have needed to drill all the way down to the water table.

On a similar note, if your studio is close to a power station you have an even bigger problem. In this case thin, non ferrous shielding like aluminum foil will not help you. Low frequency (60Hz) signals will pass right through it. Here you need a thick, high magnetic permeability material.

But, it’s not just power stations. 60Hz signals are everywhere, and rather difficult to control. In fact, they are so ubiquitous that we often don’t even notice them. Refrigerators, ventilation systems, lights, computers, etc. are continuously humming away. I’ve never tried it, but it would be interesting to look at a bunch of recordings with a spectrum analyzer and see how many contain low level 60Hz hum. I bet a lot of them do. Those brushed aluminum cases look nice and don’t rust, but steel does a better job.
 
Barefoot wrote: "At those signal strengths there might have been significant ground penetration. Your ground rods could have even been floating on WBZ! You might have needed to drill all the way down to the water table..."

It was _ugly_. That part of Needham is a thin layer of dirt over the top of granite bedrock, and getting any kind of a real ground was somewhere between "this is a freakin' major pain in the ass" and "please let me slit my wrists now". I'm sure that we _were_ floating on a few tens of volts of their AM carrier, because we never could clean it up to my satisfaction, despite all our best efforts. Luckily, they didn't want to try to record- they just wanted a practice space where they could turn on the PA without having the traffic reports be louder than the drums...

Any super-high-power transmitter can't really use just a single point ground for the tower- you need to synthesize a ground plane, which is usually done by trenching ground cables radially out from the tower base (like the spokes of a wheel) to ground rods at the other end. The further you can go with them, the more efficient your antenna becomes. I could see traces of 3 of the radial trenches from the yard, and one ended only 30 or so yards away. Ugly. Ugly, ugly. I don't want to have to do that again.

Anyway, this is probably a nonissue for just about everybody. I just wanted to use that somewhat unpleasant experience to illustrate a point: in that case, ungrounded aluminum foil would have simply become slightly warm to the touch, and the room would still have been full of hash! When you're talking about severe EMI problems every situation is different, and one size will _never_ fit all...
 
Now that was one hell of a post, I give you a ton of credit for that.

The thing about the shielding making it worse possibly... the chances of me making my shield the exact size as to be at the radio waves' resonent frequencies, are very very slim. I can say with 95% confidence that my shielding will help. I can say this because of the experience I have with shielding.

Guys, you have to remember, this is "home recording", we're not going for 100% proffesional, at least that's what I've been told. We make due with what we have.

You also have to remember, by using foil I'm leaving about 99% less gaps as what chicken wire will leave, and if chicken wire will work just fine as a shield won't foil?
 
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