Radio Interference with Audio Technica ATW R310 Recievers, Help!!!

[AlecIrwin]

I have never been more exhausted from trying to track down an issue. Let me describe the nature of the problem.

It started several days ago after I set up a sound system for a community theater musical performance. We are using 14 wireless microphones in total, some are Shure model, some are Audio Technica and a couple are Sennheiser. The system was left completely muted and idle. I was working on another project in the theater when a piercingly loud high-frequency whine filled the room. It went away a moment later. I went to the board and saw that everything was in fact, still muted. I sat by the board for a while and it happened again. Even though everything is muted, one of the receivers was getting such strong interference that it managed to push through the board anyhow. (To my understanding, in extreme cases, this is possible.) I changed the frequency on that receiver, and the problem occurred again, on a different receiver. I have spent the past few days shuffling frequencies again and again only to find that nothing I do helps.

The only receivers this seems to be a problem with are the Audio Technicas.

The theater is located in an industrial area, is there maybe some heavy machinery causing this interference?

There is no pattern to this problem. Sometimes it will happen several times in a minute, other times it goes away for an hour and comes back, at most times of the day.

Any clue? We have a show tomorrow, and I don't want to be responsible for causing ear damage to our audience...

 

[standup]

I just want to clarify this, is the receiver actually showing that it is picking up an audio signal when this happens? Or is the channel on your board showing the signal?
Also, what kind of board are you using?

Short answer, I don't know. I've never heard of something like this happening, but let me try to help.

Since it is only affecting some of the receivers, start by checking cables. It seems more likely to me that you could have an unbalanced cable somewhere farther down the line (between board and amp) that could be picking up radio interference, or there could be a problem with the amp picking up rf, like old tube guitar amps. Loose cables and jacks could also cause some obnoxious noises.

There could also be something wrong with the channels that the AT receivers are plugged into. Try rearranging how the receivers are patched and see if the problem continues.

There could be a problem with the power supply leaking DC voltage to the output, causing all sorts of noises. HOw clean is your power? A power conditioner might help solve the problem.

Honestly, I do not know what is causing your problem, but it doesn't sound like a RF issue to me. Unless the receiver is broken, try looking for other parts of your system that could be at fault.

 

[Aman121]

I could be wrong here, but my understanding is when a channel is muted on most consoles, it is electrically isolated from the mix bus by either a switch or on nicer analog consoles a relay. So while I guess its possible that signal is getting through the muted channels just by cross talk to the main bus or an unmuted channel, I wonder if the issue may in fact be with you board or other components of your PA.
That is my take on the problem, others can likely offer better advise on wireless troubleshooting.

 

[Chris15]

Please post the operating frequencies of all your systems
This may help uncover a range of RF related issues...

 

[AlecIrwin]

I am sorry that I did not post more details about the problem, I hopped on the computer really quick in the midst of final dress rehearsal preparations.

I spent some time further troubleshooting the problem, and it gets weirder.

It is definitely a radio interference problem, because the only way to solve it has been to turn off the receiver it is effecting. When this occurs, the receiver reads as if it has "locked on" to a wireless microphone transmitter, and displays RF signal and audio level indicators. I should clarify, the sound is more of a white noise than it is a high frequency whine. The strange part is, if I shut off one receiver, the problem will come back on a different receiver. The same thing has happened whenever I change frequencies. (Which I have done at least three times on all 6 receivers. There is also no pattern whatsoever as to when this problem occurs. It has happened past normal business hours, so even some strange tool or machine creating interference is improbable.

Today I happened to run into my go-to for these types of questions, (someone with an actual degree in electrical engineering) and he was just as stumped as I was. I showed him my set up, and his thought was that there was probably some device (being in an industrial area) that was causing interference. He said that I might be getting harmonics or sub-harmonics from a radio system someone else was using, (which makes sense), or perhaps some sort of automated system. Nonetheless, I have my failsafe during the show which is to power off the receiver for a moment to stop the noise, but he suggested when the show was over I call the FCC and let them know about some sort of interference in my area.

Thank you for all of your help!!!

 

[Les]

I'd still be interested to know what frequencies you're using. There is a certain MHz range that has been banned recently (in the last few years) by the FCC, and while I'm not inferring that you're operating within that now illegal portion of the spectrum, it would be a good thing for us to rule out.

he suggested when the show was over I call the FCC and let them know about some sort of interference in my area.

The FCC may be able to help narrow down the source, but I'm afraid they can't do much to eliminate it. Wireless mics operate in sort of an unprotected range. If you look in the manual, I'm almost certain that you'll see a familiar clause:

"This device complies with part 15 of the FCC rules. Operation is subject to the following two conditions:

1). This device may not cause harmful interference, and
2). This device must accept any interference received, including interference that may cause undesired operation."

Either way, I hope you get it sorted out soon!

 

[Chris15]

Yep, as Les alluded to, it may be you that's interfering with a licenced user of the spectrum and that FCC call could backfire badly...

Hence I reiterate my request for you to post your operating frequencies...

 

[BillESC]

Audio Technica's ATW-T310 receivers operate in the following frequency ranges.

C Band - 541.500 - 566.375MHz

D Band - 655.500 - 680.375MHz

I Band - 482.000 - 507.000MHz

BTW, some Sennheiser wireless units create loud white noise when the transmitter is powered off while the receiver is still on. We had this problem in a theatre I work at.

 

[Stookeybrd]

BTW, some Sennheiser wireless units create loud white noise when the transmitter is powered off while the receiver is still on. We had this problem in a theatre I work at.

That's not created by the receiver, the receiver is just doing it's job on a noisy frequency. Raise you squelch with the transmitter off until the white-noise disappears. This way if you lose a transmitter during a show, the receiver will simply mute instead of allowing white-noise to pass through.

 

[AlecIrwin]

Here are the frequency settings (as they are now) on the Audio Technica recievers -

680.000 Mhz
678.000 Mhz
660.000 Mhz
674.000 Mhz
663.000 Mhz
665.000 Mhz

This is after I have changed them a few times. I am aware that some frequencies are illegal to use, but between my school and every other group in this area I have seen use them, I figured that I didn't need to worry. Of course, I wouldn't try to use that as an excuse, and I need to be responsible for whatever operations I run. I appreciate that Les alluded that I might be operating somewhere I shouldn't be, after all, that's why I wrote here, this is something I haven't needed to deal with yet. I do not think that any of these frequencies are reserved, but I could be wrong.

It looks like I am operating on the D band.

Thank you again for all of your help!

 

[museav]

Here are the frequency settings (as they are now) on the Audio Technica recievers -

680.000 Mhz
678.000 Mhz
660.000 Mhz
674.000 Mhz
663.000 Mhz
665.000 Mhz

This is after I have changed them a few times.

How did you come up with those frequencies? While it would be nice to have an actual RF scan on site and use some of the nicer software, you can at least use some of the resources the wireless manufacturers offer such as Shure Americas | Wireless Frequency Finder, Audio-Technica - Microphones, headphones, wireless microphone systems, noise-cancelling headphones & more : Using Wireless Systems and Sennheiser: Headphones, Microphones and Wireless Systems. Those might help indicate what frequencies may be in use by licensed users and which may be good options for you to try. Some of the more advanced software will also look at intermodulation and help avoid using frequencies that may negatively interact between your wireless systems.

 

[AlecIrwin]

I chose the frequencies by scanning through on each receiver until I found a frequency that didn't display any junk in the "RF" signal meter. I will refer to those websites, thank you!

 

[Stookeybrd]

I chose the frequencies by scanning through on each receiver until I found a frequency that didn't display any junk in the "RF" signal meter. I will refer to those websites, thank you!

I have no idea what your particular spectrum looks like, so I used the 94203 zip code to start. The two FCC protected channels for wireless mics only in 94203 are TV 36 and TV 38. Tough break. But 19, 24, 27, 29, 30, 31, 33, 34, 39, 41, 43, 47 and 50 are restricted to mobile TVBDs. The D range of the AT mics is 655.5 to 680.375, which is TV44-TV48. That means that the only DTV free and mobile TVBD device free channel is TV47 in 94203. Try and make sure that all your mics exist between 668MHz-674MHz and you'll be much more interference free.


680.000 Mhz in DTV48
678.000 Mhz in DTV48
660.000 Mhz Fine.
674.000 Mhz in DTV48.
663.000 Mhz in DTV46.
665.000 Mhz in DTV46.

Now, this may be alright in your building in your area, but upon initial inspection it is a recipe for trouble. Again, try to stick within TV47 and you'll nearly interference free with properly coordinated frequencies.

 

[Chris15]

Yep, sitting on an active TV channel would do it...
There also appear to be some 3rd order 3 Transmitter Intermods at play as well

Here's a set of IMD and TV free frequencies based on a Zip Code of 94203
656.500
658.750
660.375
669.125
669.750
671.625
672.625 (spare)

 

[AlecIrwin]

Thank you!!! I will try those frequencies! However, if I was trying to use a TV frequency, why is it so "sporadic"? Wouldn't it be a constant interference, as opposed to bouncing in and out at random intervals?

 

[MilesDenison]

When you scanned through each frequency, were all of the other receivers/transmitters on/had a pilot tone active, if applicable? Once you scan through/adjust, take another couple of passes through turning each transmitter off and checking what sort of signal you have on the receiver.

Also, what is your squelch set at?

I dread using more than 20 or so transmitters in a show, for just this sort of reason. Interference is pretty evil, and finding completely clear frequencies can be a chore.

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[Stookeybrd]

I dread using more than 20 or so transmitters in a show, for just this sort of reason. Interference is pretty evil, and finding completely clear frequencies can be a chore.

Give me a call, I don't break a sweat until I hit 200.

At this point in time, purchasing the right equipment band is more important than the right frequencies. If you purchase gear that covers either of the two protected 6MHz chunks than you'll have little problem fitting 10 channels into that space. Wireless is no longer a throw-and-go part of production. Frequency planning should occur even before purchase/rental.

 

[MilesDenison]

I think in our situation, it's much worse with our video system. We run coax lines with RF modulators for video monitoring up into the booth, backstage, in the green room, etc. That hits one of our bands pretty hard.

Where are you using 200+ transmitters?

 

[museav]

I think in our situation, it's much worse with our video system. We run coax lines with RF modulators for video monitoring up into the booth, backstage, in the green room, etc. That hits one of our bands pretty hard.

A properly cabled and terminated RF video distribution system should not affect your wireless systems unless it is a matter of something like the wireless antenna cables being run along side of the video coax. If your cabled video system is radiating enough RF energy to affect your wireless then you may have problems with your RF video distribution system.

 

[MilesDenison]

A properly cabled and terminated RF video distribution system should not affect your wireless systems unless it is a matter of something like the wireless antenna cables being run along side of the video coax. If your cabled video system is radiating enough RF energy to affect your wireless then you may have problems with your RF video distribution system.

We do. Definitely

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