Chapel Sound System Receives Unwanted Radio Broadcasts

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scottmcintyre
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Chapel Sound System Receives Unwanted Radio Broadcasts

Postby scottmcintyre » Sun Jan 17, 2021 11:36 am

We have noticed that our meetinghouse and our stake center both have an intermittent issue where a radio station can be heard quietly playing over the chapel sound systems during meetings. The members that sit in the overflow area between our chapel and the gymnasium seem to notice the unwanted music most often. This is possibly because the lower ceiling in the overflow means the members sit closer to the sound system speakers.
Today it was smooth jazz. Previous weeks have featured pop/rock music as well as talk radio. We initially thought that the sound and video equipment we use for zoom broadcasts of our Sunday service were the source of the unwanted signal. Although the music isn't heard until our A/V equipment is connected, powering off all the external A/V equipment and disconnecting it does not make the unwanted music stop. In doing some testing, we found that the signal can be heard immediately after a speaker at the podium pauses speaking. It may be happening while they talk as well but it can't be heard over the speaker's voice. When the sound system is first powered on, the signal can not be heard until after someone speaks into the pulpit microphone.
As far as I have been able to tell, the only thing that we can directly tie to the presence of the radio signal is having an electrical extension cord plugged in to an outlet on the stand or having a microphone (XLR) extension plugged in to one of the two XLR inputs at the front of the Chapel.
Our zoom broadcasts use both an electrical extension cord and an XLR extension cable.
The unwanted radio sound can't be heard over the Zoom broadcast.

It may not be relevant, but our Sunday broadcast uses the following external equipment.
Rode Rodecaster Pro audio mixer
BlackMagic Design ATEM Mini HDMI video switcher
(2) GoPro Hero 8 Black video cameras with Media Mod attachments for HDMI output (cameras are powered using USB external battery packs)
Lavalier microphone clipped to pulpit mic that plugs into one of the GoPro cameras (our meetinghouse does not have a system audio out jack)
Laptop computer

If anyone has suggestions for troubleshooting or experience resolving this issue your advice would be most appreciated!

russellhltn
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Re: Chapel Sound System Receives Unwanted Radio Broadcasts

Postby russellhltn » Sun Jan 17, 2021 12:28 pm

RFI (Radio Frequency Interference) is always a fun one to chase down. You've done a lot of the legwork.

The first step is to identify the affected input. If you have access to the rack, you can watch the LEDs on the processor as it switches between different inputs.

Otherwise, what you can do is after getting the radio station to come in, try plugging in a mic with a short cord into other inputs to see if the sound goes away. Don't overlook the sacrament mic. The idea is to put a "load" on the open input just to make sure an unused input isn't the source.

Ultimately, the sound system is FM's problem. But there may be a significant delay before they can get someone out to look at it. The following is based on the idea that you can do the work without messing things up. If the vendor decides the problem is due to someone tampering with the sound system, FM may be billed for the vendor's travel (which in my case includes airfare and hotel). Needless to say FM isn't going to be happy with anyone who sticks them with an unexpected bill. So, perhaps the first step would be to undo any modifications that have been done to the system.

Next step is to look at the wiring of the inputs. Make sure the grounds and shields are intact.

Next would be to put ferret beads/coils around the wires. It sounds like what's happening is that the added wire is acting like an antenna and bringing in too much RF energy for the sound system to handle. The ferret cores will choke the signal riding ON the cable, while leaving the signal IN the cable intact. I'm suspecting the issue is with the pulpit mic as many of them have power supplies in the base. That would explain why adding a power extension cord contributes to the problem.

I'd also try to identify on what band the radio station you're getting. That makes a difference in the formula/mixture of the ferret cores you use. There's a difference between AM (1MHz) and FM (100MHz).

I'm sure there's more information about using ferret cores for RFI by doing a web search. But check the grounds/shields first. A bad job there will open the system up to all kinds of problems.
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Mikerowaved
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Re: Chapel Sound System Receives Unwanted Radio Broadcasts

Postby Mikerowaved » Sun Jan 17, 2021 4:59 pm

russellhltn wrote:...ferret cores...

Those are "ferrite cores". Looks like a spell checker got the best of you. ;)

BTW, they can be very affective at reducing unwanted stray signals from entering your sound system. Here's one example of a kit you can buy, although the "mix" isn't specified. Mount them on the end of the cable(s) nearest the sound system.
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