Interference with Audio-Technica 5000 Series mics

[MHSTech]

Well, here we were, middle of the second show of the weekend. Last nights show wasn't great because the frequencies were overlapping some, it's a new school, it's something I hadn't gotten to yet. So I come in today and the sound guy and I changed all the frequecies so they work perfect. By this time everything was flawless, we could pick up the mic from anywhere in the venue, within reason. Well we get to about 5 minutes before show and I hear this over the radio "Mike, get up here NOW". I go up and every mic is dead, just plain dead. Dead as in the reciever is picking up absolutely nothing from the transmitter. The transitters were in the same places they were before where we got 3/4 strength for the signal. During intermission we set the frequencies to a different set. No luck, so we hurry our butts up and change them back to the defaults. No luck. So we just said screw it and set up more floor mics and other random wired mics.

So what the hell is going one here? How can they work before the show and not during. Also, they weren't working when I left tonight either. This is $12k in wireless mics, so they just dicide to take a crap? Or is there something else going on? We had another AKG wireless mic that was VHF running along with this system and it was fine. Another thing was that you would only get so far from the reciever it would just drop out. The signal wouldn't fade out or anything, just be fine and then cut out when you got so far.

Let me set the scene for you. There was a awfully big rain storm moving in during the show. Most of the government communications around here are VHF or low-band. The building is wireless with 802.11G, but that's always on. The city has a wireless network covering the whole town for all the city building around town, but that is also always on. All the HVAC and other random controls for the building are wired, as far as I know. The radios we were using are FRS/GMRS. The Telex intercom system runs over UHF, but nobody was on it and the base station was on before when we had everything working too.

Any help would be GREATLY appriciated.

[mbenonis]

Sounds to me like a transmitter problem and not an interference problem, since the receivers aren't picking up anything. I'm going to assume that you tried fresh alkaline batteries in the transmitters, and that they failed to work even with new batteries. Was anyone handling the transmitters who was not experienced? I know some units have an option to be on but not emit any RF for various diagnostic purposes - is there a chance this mode was enabled? If not, and if the transmitter does not show any error codes, you might try using a radio scanner to scan to the frequency they are transmitting on to see if they are indeed emitting any RF. If they are emitting RF, then the problem is likely in the receivers. In either case, call A-T and get them to send you new receivers or transmitters ASAP.

By the way, you didn't say how many channels you were using. Based on your cost figure, it sounds to me like 8-12 channels. Are ALL of them exhibiting this behavior, or is it just some?

[MHSTech]

We have 6 recievers, but 10 mics between those (8 pack, 2 handhelds). I extremely doubt that this is a hardware issue. Why? Because they all went down about the same time. The only people I know of that handeled the transmitters were us and the actors. Even then they were locked so no changes could be made to them.

There were fresh batteries in them and there is no option to turn the RF off in the menu on the transmitter, just a Hi/Lo option.

[mbenonis]

This really is an odd problem. Basically, these are the causes of failure that I can come up with:

*The weather. It's possible (but pretty unlikely, IMO) that the storm reflected some interfering RF waves your way. However, changing the frequency should have fixed this problem, and it would have been fairly intermittently to begin with.

*The receivers are overloaded. This means that there is a signal that is so much more powerful than the wireless mics that the receiver just freaks out (This is similar to trying to whisper to someone at a rock concert). There really isn't a good solution here other than better wireless gear with better front-end filters (e.g., Lectrosonics).

*The transmitters are not emitting any RF at all. This can be verified with a basic radio scanner. If this is indeed the case, and the batteries seem to be fine, you would need to call A-T.

*The receiver is just broken. The only solution to this is to call A-T and get them to replace them.

But before calling A-T, I would try a mic and a receiver somewhere else to eliminate hardware failure as a possibility. Take them outside or to a different room and see if you get any RF. If so, there is something in the room interfering, but it's anyone's guess as to what it could be.

You might also post a message to the theatre-sound listserv to get some opinions from them. There are a number of experienced RF engineers on the list who may be able to point something out that I've missed here. Info: http://www.brooklyn.com/theatre-sound/

[RelativeMischief]

Do you have a Squelch on the recievers? If you do make sure it's set for the proper distances between transmitter and reciever.

[soundlight]

Is the whole rack run through one single antenna distro? If the antenna distro went down, all the recievers would stop receiveing.

[cutlunch]

Do each of the receivers have their own aerials or do you use an aerial splitter system? If the latter did you check the power hadn't been turned off or the aerial wire come loose. You hadn't moved anything around in the booth that might have caused sheilding of the receivers. I can't see the storm blanking all the receivers at one time. It is more likely to cause interference with signal dropout not complete blanking.

Edit:
MSHTech I wrote the above before I found an old post of yours stating you have an UHF distribution system. This just confirms my suspicions. I believe that after the tests maybe the power was turned off to the UHF splitter if you have one, or a cable may have come loose or being damaged, also check the antennas weren't knocked out of alignment or damaged.

[MHSTech]

The UHF ditro. was on at the time. It was all 6 of our recievers that went down.

This has nothing to do with the squelch or a hardware failure. This WAS some kind of interfernce or some sort. Also, I absolutly will not move the recievers or touch the wiring. They are rack mounted and if I do anything with them, I'll void the warranty on the work done by the company. I already have enough time with getting them to come in and fix things.

We ran the show again today. The mics worked fine. They were around half strength at times on stage, but overall, they were over 50%. Only thing I did different today was change the frequencies back to what they were when they worked yesterday.

[jbeutt]

Interference across your all your frequencies? What kind of range are you on? Seems like an awfully swift rush to a conclusion without actually inspecting anything.

[cutlunch]

Originally Posted by jbeutt

Interference across your all your frequencies? What kind of range are you on? Seems like an awfully swift rush to a conclusion without actually inspecting anything.

jbeutt I think the same as you that inteference that would take out all 6 receivers out at the same time is quite unusual. The only thing I can think off is if there was a really strong magnetic field induced around the receivers aerials.

The Audio-Technica 5000 actually has a built-in anti-inteference system to help minimise this problem.

I'll be really interested to find out what the interference was.