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Radio Frequency Interference Issue

Posted: Sun Jan 17, 2021 8:37 pm
by cartman
Twelve years ago, I had a whole house integrated Bose speaker system installed when my home when was constructed. The speaker system always provided a high-quality sound when connected to a stereo receiver. However, for the last few months I have had a severe Radio Frequency Interference (RFI) issue.

A local radio station is now causing radio frequency interference through all eight speakers in four rooms. This RFI even occurs when there are no stereo amplifiers, or any other electronic equipment connected to our speaker system. The station's transmitter is located approximately 3 miles away. I cannot determine why our speaker system is picking up this radio station's broadcast. When we do connect a stereo receiver to the speaker system, the radio interference competes well against the receiver output. The RFI is that loud.

I have done my due diligence by contacting the original installer, the local radio station (transmitter 3 miles away) and even the FCC. The FCC was most interested and via e-mails asked me a series of questions in an attempt to help. They asked a series of questions such as is the control box grounded, any lose wires in the control box and are all speakers working properly? None of this helped identify the issue. Everything remains properly working. I have not heard from the FCC or the radio station for weeks. I do not believe I will hear from them again. As best as I can determine, none of my neighbors are having a similar issue.

Any thoughts would be helpful or who I can contact next.
Thank you.

Re: Radio Frequency Interference Issue

Posted: Sun Jan 17, 2021 9:18 pm
by vitaflo
A radio station puts out a ton of power, especially if it's as close as 3 miles away. Most likely your speaker wires are acting as an antenna and picking up the RFI.

Two possible solutions, use shielded speaker wire or steel conduit to provide shielding, or install chokes (usually ferrite cores) to choke out the offending frequencies. What ferrite you use depends on the freq (AM or FM).

Will either of these hurt? No. Will they help? Maybe. Given the speakers were installed with the house, retrofitting these two solutions could be expensive depending on how it was installed and how easy it is to modify. And of course there's no guarantee it will work.

You're right that the FCC wants to hear from you because they have strict requirements on RFI from various sources. Any ham radio operator is very familiar with this. But you're also right you may not hear anything back on the matter.

Re: Radio Frequency Interference Issue

Posted: Sun Jan 17, 2021 9:30 pm
by David Jay
The FCC questions are “spot-on”. Something in your speaker system is rectifying the signal. A loose wire could be the rectifier. A bad ground could accentuate the problem.

A “field-fix” would be to put a ferrite bead on every speaker wire coming into the main control enclosure. That will significantly attenuate the level of signal getting into the system and hopefully make the rectified signal inaudible. PM me for more details, I hold an FCC General Radiotelephone License.

Re: Radio Frequency Interference Issue

Posted: Sun Jan 17, 2021 10:08 pm
by Mudpuppy
I have some sympathy. At my first apartment, I could pick up the phone and hear a local radio station. That was much more easily rectified, as the radio station had phone line filters for that very purpose. I just had to call them and arrange to pick the filters up at their business office.

Since this is a new issue in an old system, ask yourself what might have changed in the past three weeks. The original installer should be able to send out a service technician to make sure there are no loosened wires, damaged components, or other issues with the installation that could have brought the issue on.

If you can't find anything that has changed on your end, contact the radio station again, this time emphasizing that you have had the speaker system installed for over a decade without the issue. Focus on asking if anything changed on their end. Involve the FCC again as necessary.

Re: Radio Frequency Interference Issue

Posted: Mon Jan 18, 2021 7:45 am
by bob60014
Though you'll only need a couple of them, the ferrite cores normally work.

These and others are available from Amazon. https://tinyurl.com/y4p7cev7

Don't forget to check all the connections to the equipment , speakers also, to ensure that they're all good. After 12 years, things happen.

Re: Radio Frequency Interference Issue

Posted: Mon Jan 18, 2021 8:21 am
by Laundry_Service
Do you know the make and model of the system? Do you know if you can change frequencies?

Re: Radio Frequency Interference Issue

Posted: Mon Jan 18, 2021 9:09 am
by Call_Me_Op
vitaflo wrote: Sun Jan 17, 2021 9:18 pm A radio station puts out a ton of power, especially if it's as close as 3 miles away. Most likely your speaker wires are acting as an antenna and picking up the RFI.

Two possible solutions, use shielded speaker wire or steel conduit to provide shielding, or install chokes (usually ferrite cores) to choke out the offending frequencies. What ferrite you use depends on the freq (AM or FM).
I assume that this is AM, since the RF is getting rectified in the speakers. AM is easily demodulated by an even-order non-linearity.

I agree with the suggestion of trying (common-mode) chokes. If some of the speaker wire is exposed, a ferrite core designed to operate in the frequency range of the radio station can be clamped over the wires.

If you have any friends who are ham operators, consult with them. Many hams know a lot about this type of thing.

Re: Radio Frequency Interference Issue

Posted: Mon Jan 18, 2021 9:26 am
by NCPE
I concur with David Jay and Vitaflo on with their responses, given that you are having a problem and your neighbors are not it is probably in your system.

It is unusual that you can hear the radio station with nothing connected to the system, unless you have speakers that have a built in amplifiers. The ferrites should help, but you also may have a loose wire that is allowing the speaker wiring to be come an antenna. If the interference is present all the time it will be easier to trouble shoot that if it is intermittent.

The system installer should be able to help and determine what can be done to mitigate the RFI. If you have a local amateur radio (Ham) club they may have someone that can assist determining the cause of the interference.

(Also hold a FCC General Radiotelephone License and a lot of other certifications that I don't need much any more).

NCPE

Re: Radio Frequency Interference Issue

Posted: Mon Jan 18, 2021 11:24 am
by jimmyq
Assuming that everything is grounded correctly, I would recommend applying ferrite cores to all the cables going into the control unit (which was one of the suggestions already provided).

I assume that the radio station is AM, as that is more likely to cause the issue you describe. For AM frequencies, I would recommend using ferrites with a material type that is more effective for that range, such as the "31 material" from Fair-Rite Corp. You can do a search on Amazon for "31 material ferrite core". Clamp one these cores onto each of the input wires, including the power cable and speaker cables. If there is room to loop a wire twice through the core, then do that as it will increase its effectiveness dramatically.

This is a very effective method that we use in the electronics industry to reduce or eliminating interference when you don't have the luxury of fixing the circuits themselves.

Re: Radio Frequency Interference Issue

Posted: Mon Jan 18, 2021 12:07 pm
by Bob.Beeman
cartman wrote: Sun Jan 17, 2021 8:37 pm Twelve years ago, I had a whole house integrated Bose speaker system installed when my home when was constructed. The speaker system always provided a high-quality sound when connected to a stereo receiver. However, for the last few months I have had a severe Radio Frequency Interference (RFI) issue.

A local radio station is now causing radio frequency interference through all eight speakers in four rooms. This RFI even occurs when there are no stereo amplifiers, or any other electronic equipment connected to our speaker system. The station's transmitter is located approximately 3 miles away. I cannot determine why our speaker system is picking up this radio station's broadcast. When we do connect a stereo receiver to the speaker system, the radio interference competes well against the receiver output. The RFI is that loud.
Like many of the other responders, I am also a "Ham" radio (Advanced Class) operator, hold an FCC 1st Class Commercial Radiotelephone license and earned a BS in Electrical Engineering from U of Illinois. I worked my way through college as an engineer at WILL AM, FM, TV in Urbana, IL.

Some basic info would really help a lot:
  • Station Call Letters
  • AM or FM (almost certainly AM but it would be helpful to know for sure.)
  • Frequency
  • City of license
  • Your home location in Latitude and Longitude
    (to determine distance and bearing from station to you. You can get this from anybody's cell phone while standing on your property. CAUTION: this reveals your address, but without it we can only make wild guesses as to why the apparent field strength at your home may have changed.)
Regardless of your location the problem is yours. The station is not broadcasting any audio, only RF. Your system is not supposed to respond to RF energy, it's an audio system, not an RF system. The interference results from your system rectifying radio signals and converting them to audio.

Years ago (the mid 1980s) there were proposals before the FCC to regulate susceptibility of audio devices to RF, but this was the era of deregulation, and nothing was done. So it is your problem, or at least a dispute between you and the manufacturer of your system.

There are many possible fixes, including all of those suggested by previous posters. When I was in HS my English teacher lived across the street from WOPA 1490 AM's (1 kW power) transmitter and had the same problem. This was resolved by attaching a 0.001 microfarad ceramic capacitor from each speaker wire to chassis ground right at the screw terminal ground. Probably harder for you to do, as most audio equipment doesn't have screw terminal outputs.

This worked for that one time, we need more details. It's possible the station in your case may have a directional antenna (multiple towers) and may have recently changed its antenna pattern.

We need more input.

Re: Radio Frequency Interference Issue

Posted: Mon Jan 18, 2021 1:49 pm
by Bob.Beeman
PS:

3 miles is a quite a long distance from which to receive this kind of signal strength. Have you verified beyond any doubt that the transmitter (which you have yet to identify) is actually the source of the RF?

Re: Radio Frequency Interference Issue

Posted: Mon Jan 18, 2021 4:03 pm
by cartman
Thank you for all of the comments and recommendations. They are all valuable. In response to some of the questions;

* I am certain of the specific a.m. radio station that is causing the interference since the signal is so clear, particularly when I turn up the speaker volume in each of the rooms.
* The radio station is a.m. 1320 is located in Pittsburgh. As I mentioned, the main transmitter is only 3 miles away from my home and sends out a stronger signal to my home than the dominant a.m. station in the Pittsburgh region (KDKA).
* There are no built-in amplifiers in the system.
* I agree, the problem is mine.
* I will install a series of ferrite cores as an initial option.
* Guardian Home security services originally installed the speakers and in fairness to them, I have not had an issue for 12 years.
* Thank you for the added suggestion of contacting a ham radio operator.

Re: Radio Frequency Interference Issue

Posted: Mon Jan 18, 2021 4:16 pm
by radiowave
cartman, agree with all of the above. Curious that the speakers are picking up the signal with equipment off. One simple thing you can do before you start getting serious with ferrite, is to disconnect the wires to the back of the speaker and see if the AM signal goes away. If it does, that's likely the audio wires becoming an antenna problem. If the signal is still there with the wires disconnected from the speakers, the problem is likely in the speakers for some reason (that would be an odd finding but still within the range of possible).

I'm a ham radio operator and agree with contacting a local club. Our club has helped with community interference problems like yours.

Re: Radio Frequency Interference Issue

Posted: Mon Jan 18, 2021 4:40 pm
by meebers
From Wiki description of the station. 7000 watts. https://en.wikipedia.org/wiki/WJAS. KDKA AM is showing 50,000 watts.

Re: Radio Frequency Interference Issue

Posted: Mon Jan 18, 2021 5:00 pm
by MathIsMyWayr
I doubt that the AM radio station is in violation of the OOB emission requirement of FCC part 15. The transitting antenna cannot radiate strong EM waves in the audio frequency range, either. Your problem may originate from PIM (passive intermodulation products). Since you did not experience a problem before, loosened or corroded contact(s) somewhere the speaker cable paths might be the culprit. Can you remove, clean, and re-tighten all the contacts/joints?

Re: Radio Frequency Interference Issue

Posted: Mon Jan 18, 2021 5:41 pm
by teCh0010
So what changed?

Have you had any work on the house before right before this all started? Electrical, plumbing, roofing, etc?

Re: Radio Frequency Interference Issue

Posted: Mon Jan 18, 2021 5:59 pm
by Electron
This site has a very informative application note that may help.

https://palomar-engineers.com/tech-supp ... u-tutorial

Look for the link to "Curing Consumer Electronics RFI".

Re: Radio Frequency Interference Issue

Posted: Mon Jan 18, 2021 6:24 pm
by adestefan
Before you go down the route of ferrites double check all the connection. I bet you have the start of some corrosion on one of the connections and it’s turned into a point detector that’s demodulating the signal.

Re: Radio Frequency Interference Issue

Posted: Mon Jan 18, 2021 6:26 pm
by Thesaints
Your Bose system operates in the band close to zero- up to 20-something MHz. The station transmits on a 10 kHz bandwidth around 1.32 MHz, which is included in the band of your audio system. Cables from amplifier to speaker carry an amplitude modulated signal, so that anything you do to kill the AM station will affect your audio quality. That includes the ferrite rings. If you are not a purist for your sound, by all means try it.

The only "perfect" remedy is shielding those long cables serving your speakers and the good news is that they should already be shielded.
A test you can do (if practicable) is disconnecting the speakers and see if you still hear noise and from which speakers, which would point to direct coupling from AM station to the speaker. If that is the case and it is aesthetically acceptable, you could try to wrap the affected speakers in aluminum foil, leaving their front open.
If instead you don't hear anyhthing from disconnected speakers, coupling is through the wires. If you can inspect them, likely culprits are where the wires are connected to speakers/amplifier, check if you see any exposed copper wire. Sometimes the jack-wire junction gets damaged; try to gently play with it and see if noise increases/decreases: you may need to install a new jack, or replace the wire.
Another possibility, is the wire getting nicked somewhere along its length. Again, if you can inspect them, look for spots where the insulation looks compressed, or interrupted, or where the wire goes through some tight corner.

Re: Radio Frequency Interference Issue

Posted: Mon Jan 18, 2021 6:50 pm
by MathIsMyWayr
Thesaints wrote: Mon Jan 18, 2021 6:26 pm Your Bose system operates in the band close to zero- up to 20-something MHz.
:?:

Re: Radio Frequency Interference Issue

Posted: Mon Jan 18, 2021 7:00 pm
by whodidntante
It would be extremely useful to isolate which component(s) are being impacted by the interference. You can do this through a process of elimination.

Disconnect all current speakers from the amp and connect 1 or two other speakers to the amp via short cables.
Connect another receiver to speakers.
Disconnect all radio antennas and Ethernet connections, and basically any wire possible that still retains the basic function of the unit.
If you have a true sine wave AC voltage source other than the utility, try that. Some high end UPS units or generators would work.
Etc. You are looking for the minimal change that solves the problem, then you know exactly what to focus further efforts on.

Re: Radio Frequency Interference Issue

Posted: Tue Jan 19, 2021 12:37 am
by Bubba24
This discussion solves a 70 year-old mystery of tire chains playing the programming of a nearby radio station. They were suspended horizontally from two nails in the barn of a farm and perpendicular to the tower. I now understand how that could have happened, if unattached speakers can be activated, why not tire chains left out to dry? Thank you.

Re: Radio Frequency Interference Issue

Posted: Tue Jan 19, 2021 6:28 am
by othermike27
Bob.Beeman wrote: Mon Jan 18, 2021 12:07 pm
When I was in HS my English teacher lived across the street from WOPA 1490 AM's (1 kW power) transmitter and had the same problem.
When I was in HS a classmate lived across the street from that same radio station and claimed they could hear its programming emanating from their toaster at breakfast in the morning.

Re: Radio Frequency Interference Issue

Posted: Tue Jan 19, 2021 8:19 am
by Valuethinker
It occurs to me, for this thread, there's actually a case for wearing a tinfoil hat.

I knew there was a reason why I have so many tinfoil hats ... :sharebeer :happy :happy

Re: Radio Frequency Interference Issue

Posted: Tue Jan 19, 2021 8:45 am
by Call_Me_Op
Valuethinker wrote: Tue Jan 19, 2021 8:19 am It occurs to me, for this thread, there's actually a case for wearing a tinfoil hat.
Enveloping the head and tied to earth ground.

Re: Radio Frequency Interference Issue

Posted: Tue Jan 19, 2021 8:50 am
by Call_Me_Op
Thesaints wrote: Mon Jan 18, 2021 6:26 pm Your Bose system operates in the band close to zero- up to 20-something MHz. The station transmits on a 10 kHz bandwidth around 1.32 MHz, which is included in the band of your audio system. Cables from amplifier to speaker carry an amplitude modulated signal, so that anything you do to kill the AM station will affect your audio quality. That includes the ferrite rings.
Not necessarily. The chokes will attenuate the common-mode signal. The audio is differential-mode. Also, the ear will not respond to anything above 20 kHz (0.02 MHz), so the relevant audio is much lower in frequency than the radio waves - regardless of what anyone says.