Intermittent noise on TOA wireless mic system

[Blaise Douros]

The first thing I would check would be that there’s no RF interference–most receivers have the ability to scan for clean frequencies, and then set the transmitters to match. Also, I note that it’s happening on two channels, so it might be worth checking to make sure that those two mics aren’t set to the same or similar channels, thus interfering with each other.

How about the batteries in the mic packs? Are they nice and charged? Sometimes weird things happen on a struggling low battery.

[Mick Wall]

Cheers

New batteries in both packs, these are on channel 70 on these frequencies

Ch C 863.125 deregulated

Ch D 863.375 deregulated

Ch E 864.125 deregulated

Ch F 864.375 deregulated

Thanks

[Mark Suszko]

Sounds like a squelch? Are these mics gated at all? Do they have some kind of auto-level-control applied to them? Also, because I’m just grasping at straws, is the power supply to the receivers clean and isolated, or are these power spikes getting thru? How irregular are they?

[Mick Wall]

No level controls, power supply is pretty clean. The installation has been fine for quite some time but now we get this noise. I would say quite regular, 1 to 2 every few minutes

[Blaise Douros]

I think the first thing to look at is whether there is some faulty electrical equipment you can link to the noise. So turn off the fluorescent lights, for example–if the noise goes away, start looking for the bad fixture.

Does this ONLY happen when there are multiple mics turned on? If so, then it’s possible they’re interfering with each other–that being the case, you can start switching channels around. How close are the receivers to each other? Sometimes receivers that are stacked closely together can also cause problems.

Anyone get a new cell phone recently? This doesn’t sound like GSM noise, but it’s always possible.

[Blaise Douros]

One last thing–I found something suggesting that cell phone 4G signals sit just below the low end of channel 70, near the 863 range. https://www.soundservices.co.uk/wireless-microphones-radiomics-uk/ So maybe pushing the channel settings up to the top of the available settings, to the 865 range if possible, might help, too.

Listen to the noises produced here: https://www.apwpt.org/technical-papers/dr-h-b-karcher/lte-interference-to-wireless-headphones/index.php sounds like longer versions of what you posted, no?

[Mick Wall]

Thanks, I think it maybe the 4G issue, we have a transmitter not too far away.

I am going to try and get the radios hopefully retuned, if not I feel we may have to replace them and get some we can “licence”

[Ty Ford]

Hi Mick and thanks for reaching out. Thanks also to everyone who responded. It’s been a bit quiet here. I appreciate your thoughtfulness and effort.
I’ll add another weird possibility. The video you provided — and thanks for that! — reminded me of a situation in Boston some years back after the install of a new DAW. In that case, the timing was very cyclical; like every 10 seconds or so. It was eventually found that the new studio’s location on the third floor of the house, put it in the way of a Boston Airport radar tower some miles away that was sweeping for air traffic.

Regards,
Ty Ford

Cow Audio Forum Leader

[Blaise Douros]

Weird possibilities abound in this business. When I was working for a small studio in Monterey, California, we kept getting this weird staticky interference on our powered studio monitors in one of our edit suites. I checked EVERYTHING. Power grounding, loose connections between audio interface, ferrite on the computer’s power cables, sound card, different output channels on the mixer, different sources, but it was always intermittent and I could never trace it. Then one day, the static resolved into the local radio station–the cables were coiled in such a way that they were acting as a perfect antenna, and the powered monitors were amplifying the signal. I switched to shielded cables.

[Ty Ford]

If local RF is turns out to be the issue, using the Neutrik EMF suppression XLR connectors has worked here for blocking client iPhone induced RF into a mic cable.
https://bhpho.to/3o7an5k
Maybe try a pair on one cable….
Oh! and another anecdote! Peabody Conservatory’s BIG transformerless input console, a Sony I think, was having problems. Preamps were blowing out. It was found that the very long mic lines leading to the console from the concert hall were long enough to pick up stray voltages. They solved the problem by putting transformers in front of the mic inputs on the long lines.