Audio-Technica Wireless Problems

[Spectre7]

Okay the company I am employed by just did sound and lighting reinforcement for a high class fundraiser for the Children's Miracle Network. Here are the very basic room and equipment parameters so you can get an idea of the venue.

We located our FOH at the back of the theatre no more than 150 feet from the stage. Had 5 AT-2000 w/l units racked with no combiner and located at FOH. Channels were 1, 2, 3, 4, and 5. Channels 1-4 were handhelds and channel 5 was a beltpack with a TS cable on it for instruments that could have a 5th handheld if the beltpack wasnt needed. Mics 1 and 2 were given to the emcees and were instructed to hold onto for the duration of the show.

Sound checks went flawlessly. Changed all batteries just before show. Then during the show, just as the first act began, wireless number 1 began to cut out randomly. Checked the screen of the receiver and it showed it wasn't using antenna A or B. Then when it would cut back in, it would show either A or B just as it would when it was operating normally. Had the guys back stage swap batteries again just to be safe, and then it did the same thing during the second act. Then for the 3rd, our beltpack just started cutting out. We then concluded it may be RF interference overpowering our equipment so we changed the channels to 20, 19, 18, 17, and 16. The same problem occurred with the same mics. Also, these mics were purchased brand new about 4 months ago and have had light use and been kept in a rack case the entire time.

I've never had any problems like this before, and I use AT-2000's and 3000's very frequently and they always perform well.

 

[FMEng]

You might want to check your channel frequencies against the UHF TV channels in your area. A strong digital TV signal can wipe out your receivers. First, get out the book for your wireless receivers, and find out what frequencies are used for the channel group.

Then, go to the following web page to convert from frequencies to TV channels.
Television Frequency Table

Then, you'll need to see if there are TV stations broadcasting on or adjacent to the TV channels your mics use. Note that with digital TV, the TV channel that is advertised is NOT the channel they actually broadcast on.
TV Fool

Use the channel number called "REAL," not the one called virtual. This takes a little work, but not taking these steps can lead to surprises like the ones you had. This kind of thing is more of a problem now because digital TV doesn't make the tell tale sound of sync buzz in the receiver the way analog TV did.

The other thing I am suspicious of is that you didn't use antenna distribution. That increases the likelihood of IF frequency (local oscillator) leakage from receiver to sneak into another and cause interference. With five receivers in close proximity, that is a real possibility.

Okay the company I am employed by just did sound and lighting reinforcement for a high class fundraiser for the Children's Miracle Network. Here are the very basic room and equipment parameters so you can get an idea of the venue.

We located our FOH at the back of the theatre no more than 150 feet from the stage. Had 5 AT-2000 w/l units racked with no combiner and located at FOH. Channels were 1, 2, 3, 4, and 5. Channels 1-4 were handhelds and channel 5 was a beltpack with a TS cable on it for instruments that could have a 5th handheld if the beltpack wasnt needed. Mics 1 and 2 were given to the emcees and were instructed to hold onto for the duration of the show.

Sound checks went flawlessly. Changed all batteries just before show. Then during the show, just as the first act began, wireless number 1 began to cut out randomly. Checked the screen of the receiver and it showed it wasn't using antenna A or B. Then when it would cut back in, it would show either A or B just as it would when it was operating normally. Had the guys back stage swap batteries again just to be safe, and then it did the same thing during the second act. Then for the 3rd, our beltpack just started cutting out. We then concluded it may be RF interference overpowering our equipment so we changed the channels to 20, 19, 18, 17, and 16. The same problem occurred with the same mics. Also, these mics were purchased brand new about 4 months ago and have had light use and been kept in a rack case the entire time.

I've never had any problems like this before, and I use AT-2000's and 3000's very frequently and they always perform well.

 

[mbenonis]

What he said. I have nothing more to add really, FMEng hit all the key points. Hmm, I really should add a link to TVFool to my FAQ...

 

[waynehoskins]

Coordination would be my first guess, though that wouldn't tend to be as intermittent as described.

There's been talk about white-space devices for some time now. Are any of those actually in production?

Cross-polarized antennas maybe? How were the receiving antennas oriented? Where were the ends of the antennas pointed? That would tend to explain intermittent dropout of all on-channel RF instead of reception of an unintended signal.

Any other radios there? Cell phones don't usually mix into TV band, but other things might.

Could also be front end overload, possibly in-band, could even be out-of-band if the interfering signal were strong enough and the front ends of the receivers aren't very tight.

At 150 feet, I'd think you'd want to use gain antennas with an antenna splitter. Who knows?, it could simply be body shielding from the audience since the transmitters are so low-power and so far away.

 

[BillESC]

From AT's web site:

The following Wireless channels/frequencies should work in this area:

Series: 2000 Channel Frequency (MHz)
1 - 3 656.125 - 660.000
4 - 5 662.125 - 665.125
6 - 7 669.750 - 671.500

I don't know the last time the application was up dated. Channel # 2 certainly should not have been used.

 

[NUSound]

FCCInfo.com is where I go to find problematic TV channels. It's updated quite a bit and has several search options. BTW, it is not published by the FCC.

 

[mbenonis]

Cavell Mertz also had a Google Earth plugin made for them that shows many different types of broadcast-related licenses on a map, including microwave links. Very, very useful.