Anyone with knowledge on RF Interference? I’m giving up, please help.

[galli]

Although I love my Dynaudios BM15a, I’m up to return it. Cannot solve the strong radio interference. Impossible to work with.

Have already made a dedicated electrical connection, with no results. Besides, the speakers are connected on a Furman.
I believe the interference is being picked up by the speaker itself (not by the electric net).

Anyone with knowledge of RF interference to suggest any solution?

Really appreciated.

[Kiwiburger]

Get a local expert to help you out. From your post, I don't think you would have enough electronic experience to continue by yourself.

There are so many possible questions that should be asked - here are some obvious ones:

Is it a radio station? Or ham operator? Or Radio Telephones?

Normall it's high gain stuff that pickups up RFI - what are you monitoring, and are you sure that the problem isn't further back? E.G. - if you are only monitoring a stratrocaster plugged into a POD, I wouldn't be blaming the speakers.

A Furman could be anything - they make a range of products, and most are useless for RFI.

Your electrical ground can act as an antenna. An isolated ground reseptacle might help - talk to a registered electrician who knows about audio.

Are you using balanced sheilded cables???

[sismofyt]

quite a lot of internal amps in the powered speakers are not well sheilded, some only use the heatsink on the back. you could try to reduce the bandwith of the amp with a simple first order filter, but you need a (or to be) tech and preferably you need a schematic. have you tried contacting dynaudio?

have you tried moving the speakers around? different cable? are you going balanced? are you sure it's the speaker?

maybe ferritcores around the cable will do it...

[Jim Williams]

Does it happen when nothing is connected to the speakers? If not, it's the cabling or something external.

Jim Williams
Audio Upgrades

[galli]

[QUOTE=Jim Williams]Does it happen when nothing is connected to the speakers? If not, it's the cabling or something external.


Yes. Same interference when nothing is connected to the speakers. So I guess it confirms that the interference is being picked on the speakers, right?

It’s a radio station (more than one, from what I could identify).

I guess I’d need a tech expert to tweak the speaker…

Is there any other thing that I can try? Any electronic device able to block RF signals?

I contacted Dynaudio a while ago. They guaranteed the interference was coming from the power line. I then made a direct connection from my home’s main power to the studio. No changes…

Thanks a lot for the help.

[Kiwiburger]

Are your home and studio on the same property? If so, they probably share the same RFI contamination.

It could just be the ground - worth lifting to see. If it's the main offender, put in a dedicated ground stake for your audio stuff.

Otherwise a very strong RFI filter might be needed - consult an electrician. Most of the appliance type Furman boxes are toys that achieve very little. The serious industrial strength stuff is what you need. It will probably benefit everything else in your studio - if it can affect speakers, it can probably affect preamps and everything else.

[galli]

Originally Posted by Kiwiburger

It could just be the ground - worth lifting to see. If it's the main offender, put in a dedicated ground stake for your audio stuff.

In pratical steps, how can I "lift the ground"? (sorry the lack of knowledge).

And a dedicated ground stake... is this a filter? I do have a furman, but it's probably really just a toy...

Thanks.

[synapse]

That's about right. If you disconnect all the audio input cabling (excepting power) to the back of the BM15a's and with them powered on you STILL get the interference "radio stations",and being sure to disconnect the actual monitor-end of the cable, not just unplug from console to avoid the antennae effect of the cable to the monitor, then it is most likely a grounding problem.

I have exeperienced this before. Some areas offer a poor earth-ground due to soil conductivity problems. In one case it took a 30 ft copper rod/bar to be inserted into the ground outside the premise and then attaching that new earth ground to the premise electrical panel to get a proper ground circuit that would draw off the interference.




s.

[Kiwiburger]

In pratical steps, how can I "lift the ground"? (sorry the lack of knowledge).

That's really one of those questions where, if you have to ask, you shouldn't be playing around with that stuff. AC power can kill you very rapidly if you don't know what you're doing.

Can you borrow somebody's UPS, and run your monitors off batteries for a while, to see if the radio goes away? Make sure there is absolutely no connection to an AC outlet - otherwise the ground would be still connected and possibly carrying the RFI.

[overbias]

Can you identify the station(s) you are hearing? AM or FM? How close are their towers to your location?

RFI is a strange thing with tons of variables.

Jack

[thethrillfactor]

If you can identify the radio station call up the station manager and complain.

Here in the states there are rules to enforce this.

[thethrillfactor]

Originally Posted by Kiwiburger

It could just be the ground - worth lifting to see.

Please do not do this!!!tutt

[Kiwiburger]

Why? Because it might help solve the problem?

I didn't actually specifiy whether to lift the ground on the audio or the power. And I did suggest that if he doesn't know how to do this, he shouldn't do this at all.

But the practical reality is that audio engineers often lift the ground for troubleshooting AC power issues.

I find it unbelievable that anyone would ever get anywhere by complaining to a radio station. They are liscensed to transmitt, and no doubt are complying with every little rule and regulation. I don't see them dropping their power or anything just because somebody complains.

Power lines act as antenna. I used to make crystal radios when I was a kid, and I found a connection to ground was just as effective as an antenna. Electrical grounds are often connected to waterpipes, hot water tanks, steel roofs etc. The actual ground spike is often dried up and not working, so you basically have this massive network of wires and antenna, randomly tuned to all sorts of frequencies. Not the most ideal thing to connect to your audio cable shields.

A dedicated ground spike - well watered in moist ground - with short high quality cables can solve a lot of audio problems.

[Jim vanBergen]

While Thrill's plea is ABSOLUTELY right, you can TRY doing something else: replacing your compromised ground with a replacement ground. You'd have to get a licensed electrician to do this legally, but it takes very little time. He needs two ground lifters that have the ground wire coming off to a spade lug, bond them both to a 12gauge 600V rated mains wire, and solder THAT wire direct to a copper stake you can put in your basement, or find the the clean water mains pipe coming into your establishment and bond it to that. TREAT THE WIRES AS IF THEY ARE ALL LIVE, ALL THE TIME!

Most importantly, don't risk your life over a grounding issue. If in doubt, sell the speakers.

[thethrillfactor]

Originally Posted by Kiwiburger

I didn't actually specifiy whether to lift the ground on the audio or the power.
.

This is the problem bro.

Its a big one.

All it takes is a short circuit and our friend in Brazil will be no more.

Lifting the audio ground may only work if its a star ground setup and still this may not solve the issue.

His best bet is to go one by one on the gear.


Take everything out of the control room and check each piece one by one.


The culprits can be any digital gear,computers and modems, the light dimmers, unbalanced gear or speaker cables.


Check these first and see what happens.

[Kiwiburger]

I think he's already identified that the powered speakers, unconnected, pick up a radio station.

Unless there is a fault in the speaker amp circuity, there must be a strong RFI field directed into the speaker. The power lines/ground are an obvious conductor of this RFI field.

While it can be useful to find out which radio station is responsible, I can't imagine the problem can be resolved. Not without a laywer, and lots of time and money.

The reason I suggest a UPS (uninterruptible power supply) is that it can be used as an alternative source of AC power while disconnected. If the problem goes away when the speakers are powered from a UPS, you know that the AC power is carrying the RFI.

Maybe it's just easier to return the speakers and buy another pair. There's an element of luck and design which can avoid a tuned resonant circuit. Or maybe you'll just get a different radio station.

[thethrillfactor]

Originally Posted by Kiwiburger

While it can be useful to find out which radio station is responsible, I can't imagine the problem can be resolved. Not without a laywer, and lots of time and money.

Well here in the states there are FCC rules how powerful a radio station can broadcast.


All of the FM stations try to out do each other during the crucial hours so they tend to over broadcast to come across louder to the listener.

If they are in an area where they shouldn't be you can call up the station manager and complain and by FCC rules they have to turn it down.

I don't know what it likes in Brazil but its possible they have the same rules.

[dshay]

I worked at a radio station as a cheif engineer of a college radio station (engineer apprentice), and I can tell you, there is probably no legal recourse for what's happening to our man here.

IN most likelyhood, the radio stations in the area are operating well within their licensure, and it's a problem either within his piece of equipment, as kiwiburger explained rather well, or, within his electrical system of his home.

Theres a good chance they didn't ground the facility properly. You might be on bedrock, the water table is really low, or the electrician was lazy and not up to code.

Jim VanBurgen, why would you explain the method of doing something that one of these kids is going to kill themselves with? I know you put a caveat of hiring a licensed electrician first, but why did you need to explain the method after that? Just enough information to make them dangerous. You could've left it at hiring a licensed electrician. All these guys should be doing is playing with audio level voltage, which you can stick in your mouth and lick all day long. Unless they're a geek slut, and even then....

Now, here is some valuable information for all you studio engineers.

There are two types of transmission that could be causing this. The regular radio spectrum, wavelengths from 88.1mhtz to 108, which is usually propegated omnidirectionally, or in directional, kindof a cardoid lobe, for miles upon miles.

The other type of transmission is if the studio is at a different location than the main transmitter, they'll use a Studio to Transmitter Link (STL) to send their radio signal from the studio to the transmitter. I'll get to why this is important soon.

Sometimes your gear design, circuits will act like an antennae for certain frequencies, as kiwi was explaining. Othertimes your instrument chord is just the right lengh or improperly shielded, or there are ground issues within the particular equipment. This is your problem, not the FCCs or the radio stations.

Radio waves are propagated by magnetics. Antennaes pick this up with the electric concept of inductance. Magnetism causes pieces of metal to have an electric charge. The wave of this charge can be picked up by an antennae, interpreted and is analogous to sound.

The ground of your home is supposed to take care of this. However, there are some factors that might make things worse.

STLs are rather powerful and directional. they operate at the 950mhtz spectrum (the length of the waves) and can be pumped up to around 10 watts. If your home or studio lies directly in the path of one if these, it might cause issues.

If you have radio interferance, find out what radio station it is. Go down to that radio station, and ask to see their Public Inspection File (an FCC requirement that they upkeep and keep it open for your inspection any time they are broadcasting). Ask the engineer to show you the STL layout map of the area. All radio stations are required to have the coordinant of their studio and their transmitter on file, as well as a map of all the STL pathes in the area. See if your home is in the path of an STLs signal(particularly the station you can hear broadcast through your amp).

This wont help you all that much if you find out the STLs are pointing directly at you other than tell you what's likely the cause. This is more handy in helping decide if you should buy a home or studio in particular areas. Find out the path, and know that the pattern radiates out about twenty degrees.

But proper ground, shielded balanced cables and equipment that is well designed usually takes care of STLs if you're in the path.

Listen to the advice Kiwi is giving.

Oh, and another thing, the engineer at that station has probably delt with RFI extensively and can offer some advice with dealing with it. It's going to be the same advice Kiwi is telling you though.

[Jim Williams]

If it's the AM band, here in the states the transmitters are forced to power down at around 5 pm due to atmospheric changes that reflect AM radio energy back to earth. Many of the non clear channel stations that are 50k watts during the day power down to 5k watts at night. Does this rfi change between day and night?

Don't mess with Brazil grounding yourself, hire a smart electrician.

As one salesman once said; "Death is bad for repeat business".

Jim Williams
Audio Upgrades

[galli]

OK.

I borrowed a UPS and ran the monitors off batteries for a while… nothing changed at all. Same interference, which is distinctively a FM radio station.

What that means? Could it mean that the problem is entirely on the speaker and that I can forget about asking a tech to lift the ground?


Thanks for all the help so far.

[Kiwiburger]

That information from dshay is excellent advice.

I would think that if the speakers, running off battery power, and with nothing else connected, still pick up that radio station, you should replace the speakers.

As dshay said - you could be in the direct path of a Studio to Transmitter Link. You could find out as he suggested, but it probably won't change much.

Properly designed, shielded & balanced & grounded equipment won't be affected. Your speakers either have a fault or a design weakness, or just bad luck to have some circuitry resonating at he same frequency as this transmission. You could try another similar pair, or try a totally different brand.

I would still get an electrician to make sure you have a solid earth connection for your electrical ground. Perhaps a ground spike that you can water from time to time to stop it drying out.

[Jim vanBergen]

Oh, COME ON Dshay. If you're going to flame me, at LEAST spell my name right! tutt

I wrote a legitimate response with a proper caveat in response to AC grounding, an ACCURATE and FACTUAL response as to basic grounding issues since its obvious he has a two fold problem, RFI and AC ground, and I showed respect for other opinions whether I agree with them or not.

A decent engineer OR a blooming idiot can take what I wrote and either a) ignore the warning and possibly electrocute themselves, or b) use it to explain to a licensed electrician what the goal is and how to achieve it quickly and efficiently.
That's why I wrote my response.

I was pleasantly surprised that you show a decent knowledge of broadcast technology and RF, though none of us who are responding knows intimately what the communication and broadcast laws are in Sao Paolo. Soooooo, I suggest he look at:

Brazil's RF Regulatory Body,
http://www.anatel.gov.br/home/default.asp

and the frequency allocation:
http://www.anatel.gov.br/Radiofreque...CodTopicoFim=1

to have a better understanding of his countries policy and current RF allocation.

Now, Dshay why do you call Galli a KID? Look at his link and you'll recognize a professional ADULT who will appreciate decent advice, although your tendency to dispute anyone elses' opinion makes you sound a litte insecure. Are you expecting that Galli is a 15 year old high school student? Get real! Even if Galli WERE a child, basic AC grounding is easily found online, at Home Depot in any Home Electricity text, or perhaps in Phillip Giddings' industry standard textbook. He could get my answer from a hundred easy locations. Like FM transmission, building main AC is not rocket science. As a former college radio engineer apprentice, you have enough to know that mains AC can kill you, and MY point is NOT to lift the ground, as had been suggested before me, but to have a licensed electrician install a PROPER & LEGIT replacement ground, which has a greater chance of improvement that trying to fight city hall, which is all you will achieve if you get into a pissing match with the chief engineer (be it an apprentice or not) if he can get that far, with a local AM/FM transmitter.

[QUOTE=dshay]I worked at a radio station as a cheif engineer of a college radio station (engineer apprentice), and I can tell you, there is probably no legal recourse for what's happening to our man here.

(snip) Jim VanBurgen, why would you explain the method of doing something that one of these kids is going to kill themselves with? I know you put a caveat of hiring a licensed electrician first, but why did you need to explain the method after that? Just enough information to make them dangerous. You could've left it at hiring a licensed electrician. All these guys should be doing is playing with audio level voltage, which you can stick in your mouth and lick all day long. Unless they're a geek slut, and even then....

Now, here is some valuable information for all you studio engineers. "

--------------
Nice way to assimilate with the rest of the Gearslutz, and believe it or not, I look forward to meeting you at AES.

Jim (MY REAL NAME) vanBergen


PS- Galli, I hope you solve your problem on the first try with professional help, and can stop asking us for opinions on RF and grounding because, like *ssholes, everybody has one.

[quincyg]

to add a new ground to your main is very simple. buy a ground rod, 10' or so and you pound it into the ground next to your old ground rod. then you just attach your old ground wire to the new rod. really nothing very serious or dangerous, to the best of my knowledge. or you can add it in addition to the old ground. ask the guys at the electrical supply house what you need.

[quincyg]

also go pick up a $5 outlet tester and see if your outlets are all grounded correctly. they have a couple of lights that indicate the status of each receptacle.

[overbias]

I've fought this many times over the years. Contact the station and ask them where their transmitter/ tower is located. Any non-linear circuit will act as a detector of RF signals (could even be a rusty nail in a fence). If they are extremely close, you may be in trouble. My best guess would be that they are close and you are being inundated with RF. In this case, you're in trouble. I would agree, DO NOT mess with the grounding.

two cents from an old fart....

jack

[Kiwiburger]

If he was being inundated with excessive RFI, you would think that everything else he owns would be picking up the same station. Monitor speakers are not huge gain amps, and should have balancing circuitry and magnetic shielding (so they don't upset CRT monitors).

If the RFI was excessive, I would have expected all his other equipment, especially unbalanced stuff, guitar amps, mic preamps, mixers etc to suffer the same problem.

I would expect changing the monitors would solve the problem. Maybe it's a fault, or just bad luck.

But improving the ground is usually very worthwhile for all audio and video circuits. The advise to NOT do this is presumabably just SAFETY advice. That makes perfect sense - if you don't know exactly what you are doing, get an electrician to do it.

A bad ground could very well be compounding the problem.