RF interference help

mikedaul · Post by **mikedaul** » Wed Jan 25, 2006 4:39 am

Hello - I have a small (one bedroom) project studio in my house, which was built in 1980. I have a terrible amount of RF interference (in the form of a radio station) that comes in through my guitar amps and my monitors. I've tried ferrite beads and an isolation transformer from ebay, both did little to nothing. I do have a dimmer in the room, but I keep the lights off and still get the radio stations coming in. This bedroom studio is upstairs (two-story home). I also get the radio station noise occasionally in my stereo downstairs, but it is not nearly as bad as upstairs.

I recently had a new oven range + microwave installed (which required a new dedicated circuit) and asked the installer guy about improving the ground to the house (and explained the problem). He was not very helpful.

Short of moving, or building a faraday cage in my room, what can I do to get rid of the damn radio station? Would a balanced power device (equitech/furman/etc) make a difference? Should I pursue another electrician about improving the ground to the house?

Thanks very much for any advice!!

Post by **Aaronw** » Wed Jan 25, 2006 5:27 am

Greetings and welcome to the site.

How far from the broadcast tower are you?

Short of a faraday cage, a tech gave me a few ideas about another option for RF.

Delta Ground.

Option 1: Get 3 copper ground rods, and drive them in vertically in a triangular pattern (about a foot apart from each other), tie all 3 rods together. Also, (a little more difficult doing vertically) dig out the ground and mix the soil w/ copper sulfate.

Option 2: Same as option 1 w/ 3 grounding rods, tie them together in a triangular pattern about 1 foot apart or so, dig as deep of a hole as you possible can, attach the ground wire to the rods, bury the rods horizontally, and mix the soil w/ copper sulfate. Over time, the copper sulfate is attracted to the copper, allowing one large ground plane.

I haven't personally tried these yet, so I don't know the results, but it made some sense.

Also check all your groundings on your equipment.

mikedaul · Post by **mikedaul** » Thu Jan 26, 2006 5:42 am

Thanks for the help and suggestions!

There is a TV broadcast tower a little more than a mile down the road, but so far as I know it's only for the local pbs station, and the interference I hear is definitely a top-40 radio station (I don't recall the station name/frequency, but I've matched it up before).

Here's the google map link:
http://maps.google.com/maps?f=d&hl=en&s ... tnG=Search

Am I just SOL here?

Any ballpark of what an electrician would charge for installing a grounding scheme like that? I'll help dig the hole

If it is more than $1000, would a balanced power box like the furman make any difference?

knightfly · Post by **knightfly** » Thu Jan 26, 2006 6:24 am

Balanced power might help, but it's kinda an expensive experiment -

exactly WHERE did you use ferrite beads, and how? If it's riding in on your power, you might need the beads around your power conductors where they enter the room if you've not already tried that (VERY CAREFULLY)

Does this station come in only when mics are up, or always? Guitar pickups live, or does it matter?

It might cost around a couple hundred $ for the electrician to redo your ground, but if the RF is riding your hot leads that won't help much if at all.

For a proper sheild (faraday) an FM station would need around 20 mesh per inch copper, and it ain't cheap - $2 per sf for what you'd need, check out this

http://www.twpinc.com/twp/jsp/product.jsp?type=11

specifically the 48" wide, 22 x .015 copper at $800 per full roll (400 sq ft) which wouldn't do your entire room - I'm not sure if a partial, line of sight shield would help that much. I'd think at least one wall, floor and ceiling would help some, not sure how much.

Maybe as a test, you could order their minimum (25 sf) for around $75 and try moving a large chunk around your room with speakers up, to see how it works ??!?

Also, that site offers a book suggestion that might help - click on the link,

"All you need to know about RFI Shielding", and scroll to the bottom of the page.

HTH... STeve

mikedaul · Post by **mikedaul** » Thu Jan 26, 2006 1:47 pm

Thanks Steve!

On my monitors, I've got 1 ferrite bead on the power cord and two on the input cable (xlr). I forgot to mention that the "reception" is sometimes not as bad as other times. For example, tonight I can barely hear it through the monitors.

As for the amps, I've tried beads on both the power cord and guitar cable. The amps are definitely worse than the monitors.

For both monitors and amps, the radio signal only shows up when an input is plugged in. If the amp/monitor is just powered on (with nothing attached to the input) I hear nothing. As soon as I plug in a cable I get the radio station. This is true of both tube and solid state amps, but it is worse with some than others (I have 7 tube amps and 2 solid state).

Also, another interesting observation, if I touch the jacketing of the guitar cord the "reception" goes away to a degree. Having an instrument attached to the other end of the cable makes no difference.

If it's riding in on your power, you might need the beads around your power conductors where they enter the room if you've not already tried that (VERY CAREFULLY)

This sounds interesting. But if it requires any house wiring knowledge, I'll leave it to a pro. I'll definitely check out that book as well.

One last bit of valuable info. The offending station is WDCG (in Raleigh, NC). (here's their website: http://www.g105.com )
And according to this site, the damn station does indeed have their antenna alongside the wunc tower: http://www.fybush.com/site-030807.html

"Public TV comes from the University of North Carolina's WUNC-TV (Channel 4), the flagship of the statewide "UNC-TV" service - and its tower sits on Terrells Mountain, southwest of Chapel Hill, where it was presumably placed to provide some service to the Triad as well.

Today, it shares the ridge with WUNC-FM (91.5), Durham-licensed WDCG (105.1) and Burlington move-in WRSN (93.9); we don't have a good picture because it was pouring rain and foggy when we visited!"

Is it possible to selectively block these frequencies in my AC?

Also, some fcc info:
FCC Link

The copper mesh is also very intriguing. There's no way I could afford to do the whole room (although it is small).

Thanks SO MUCH for your help with this!

knightfly · Post by **knightfly** » Thu Jan 26, 2006 8:50 pm

Here's a real cheap test - go to Homely Despot and buy a male, "U" ground power plug like you'd put on the end of an extension cord - get one that has actual screw terminals, such as the one on this page (just the black and white plug is all you need)

http://www.hifi.org.uk/products/mp_prod ... eos_hubble

Then go to Radio Shack and ask for at least three 0.01 uF, 1000 volt or greater, ceramic capacitors - more if you're fumble-fingered

I scrounged around in the back and found enough stuff to illustrate what you need - the following pix are in order of operation, and I'll explain each -

Pic 1 is an Arrow-Hart 120 volt plug, the Hubbel ones are similar and either will work.

Pic 2 is the rear of the plug, with cap removed (3 captive screws, seen sticking out in pic 1)

Pic 3 is the plug with the cable strain reliefs (3) spread out for better visibility - this is a new plug and I don't want to ruin it for normal use, but YOU would cut these off flush with the body of the plug.

knightfly · Post by **knightfly** » Thu Jan 26, 2006 8:56 pm

Next, in

Pic 4 - These are the capacitors you need

Pic 5 - A closer view

Pic 6 - Two caps held together before twisting leads to join them

Pic 7 - Leads bent across each other to make twisting easier

Pic 8 - First pair of leads twisted together

knightfly · Post by **knightfly** » Thu Jan 26, 2006 9:13 pm

Pic 9 - Shows the last pair of leads to be twisted together - we're making a TRIANGLE here.

Pic 10 - Shows the assembly, ready to be trimmed short enough to fit snugly into the three holes in the power plug - one twisted pair of leads per hole.

Pic 11 - Shows the leads being trimmed.

Pic 12 - Shows the assembly inserted in the connector holes, ready for screws to be tightened.

Pic 13 - This is one of the screws to be tightened - hold the caps down so their leads stay in the holes while you tighten the screws. It doesn't matter which pair of twisted leads goes in which hole, just so connections are tight and short enough so they DON'T TOUCH EITHER OF THE OTHER PAIRS.

Next, after making sure you've cut off those three "fingers" I mentioned, you can cut a small piece of foam to fit the rear hole of the cap, and install the cap on the plug. The three screws sticking out in Pic 1 should be tightened evenly to do this.

Then comes the scary part -

Just kidding - this isn't going to hurt a bit - just plug the device into the same outlet you're using for your gear - if you want, do it with the power on so you can hear if it helps the noise.

This isn't dangerous at all, even though it sounds like it; that value capacitor sees your normal 60 hZ power as DC, and blocks it so it's NOT a short. However, to the 105 MEGAhertz RF signal, the caps ARE a short - if the noise is riding your AC, this should make a noticeable amount of difference.

Needless to say, do NOT put this device together while it is PLUGGED IN

unless you want to be considered for the posthumous DARWIN awards; however, it's perfectly safe to plug it in once it's been assembled completely.

Good luck... Steve

mikedaul · Post by **mikedaul** » Thu Jan 26, 2006 11:08 pm

Steve - thanks so much! Now I have a fun project for the weekend

I'll report back on any success or lack thereof.

mikedaul · Post by **mikedaul** » Sun Jan 29, 2006 10:27 am

Well, I built the plug contraption this afternoon and sadly it didn't help with the RFI. I could hear a slight pop sound through the speakers when I plugged it in (and removed it), but other than that I noticed no change.

At any rate, I greatly appreciate your help with this!

Are there any other things I might try, or is it time to call the electrician?

Thanks,

-Mike

knightfly · Post by **knightfly** » Sun Jan 29, 2006 8:46 pm

Before you do that, do you know if your building's cold water supply is copper, and if so is it continuous to where the water supply goes into the earth? IF so, you may be able to buy a couple of clamps and just connect your power ground directly to the water pipes.

I doubt seriously if you'll find ANY electrician that can help with RFI problems, but if your ground is clean and tight then maybe a more serious filter will help - here's one such option

http://www.mfjenterprises.com/products. ... d=MFJ-1164

I'd still get that book, there may be some common things I've not thought of (most likely

) that could solve it for small change... Steve

Post by **Aaronw** » Tue Jan 31, 2006 12:28 am

Are your monitors shielded?

As far as guitar amp, you might try the aluminum foil trick. Just be careful not to shock the shit out of yourself.

chrisgraff · Post by **chrisgraff** » Thu Feb 16, 2006 9:51 am

Hey all,

I just stumbled on to this topic. Some questions:

I'm just about to have the electric and plumbing redone in my detached garage (yes, I got permits

).

Is there anything I can do now to ensure I don't have similar problems down the road? I assume asking my electrician about delta ground would be a good place to start.

Is there anything I can have the plumber do to help? I do have copper supply lines, coming underground from the house, up into the attic, and down to kitchen/bathroom (not good, I know).

The electrician is starting in two days....any advice now would be appreciated!

knightfly · Post by **knightfly** » Fri Feb 17, 2006 2:26 am

Delta ground? Do you mean star ground?

I would print out the thread(s) on star grounding here, and discuss them with your electrician - if he doesn't think it's necessary and won't do it, find another electrician.

Copper water pipes and your ground system should all be bonded together, BTW - but this doesn't change the need for a single, common ground point for all your electric supplies in the studio... Steve

Don T · Post by **Don T** » Wed Mar 01, 2006 3:58 pm

Hello:
You can't always count on your copper pipes either. Most cities are replacing supply lines with plastic pipe. More than once I have found a breakerbox tied to pipe that did not go out underground. That's why most building codes require ground rods. Here in Portland that means 2 rods.