cell phones

spong8

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Joined
Jul 23, 2006
Can Cellphones dirupt a wireless mic system?

If it does how can you keep this from happening, besides asking people to turn off there cell phone.
 

Foxinabox10

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May 1, 2004
Location
Boston, MA
The answer is yes. And unfortunately there is no legal way to stop the cell phones from interfering. The only way that I know of would be to scramble the signals in the airways, but that is illegal.

The way high-class professional shows get around it is they're are normally allocated special frequency bands that are much cleaner signal-wise and they have much better microphones that operate very well using a couple of different frequencies so that if one drops, the connection is still solid on the other.
 

mbenonis

Wireless Guy
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Location
Chicago, IL
Yes and no. Cell phones cannot directly interfere with the wireless link between your mic transmitter and receiver, because they are in different frequency bands and your mic receiver filters it out. However, cell phones CAN inject noise into your mic lines and cause beeping in your system. Because of this, we usually lie to the audience and tell them that their cell phone "will interfere with the wireless microphones used in this production."

Professional shows do not have access to any frequencies that we do not have access to - they simply plan their system out better and use better equipment (read: more expensive equipment). They also, as Foxinabox said, sometimes have two transmitters on a person to minimize the risk of losing the mic.

Examples of wireless systems used in high-end professional shows include Lectrosonics Digital Hybrid Wireless systems and the Sennheiser 5000 series systems.
 

Foxinabox10

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May 1, 2004
Location
Boston, MA
Actually, mbenonis, many professional shows do have access to different frequencies, especially in high-show traffic areas like on Broadway. I talked to the sound operator when I saw 42nd Street and she said they were running over 70 wireless mics (including 13 implanted in people's shoes to pick up the tap) and because of the large number that they, and every other broadway show uses, they were given access by the FCC to more frequencies than the average sound engineer is given access to. All of their microphones had to be specially ordered to accomodate the different frequencies.
 

mbenonis

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Really? I wasn't aware of that - I stand corrected. Do you know what frequency bands they used?
 

Bob

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Jul 24, 2006
Location
chicago
Things to try to help with interference issues...
ban cast members from using them during shows, AND make sure that they are turned off!
always make sure that your not trying to use an active TV channel in your area (it's bitten me in #$% a few times!)
keep receivers on stage as close as possible to transmitters (and away from the audience.)
keep any antenna cables as short as possible.
with multiple mics, try to use an active antenna splitter with a band filter.

try reading thru some of the FAQ / Knowledge Base on www.shure.com
you may pick up some hints there.
 

PhantomD

Joined
Mar 3, 2006
Location
Brisbane, Australia
We have 8 shure UT systems in our permanent wireless mic system.

Last year, we had trouble with a couple of them dropping out (read: the receivers and transmitters were beside each other, receiver on, transmitter transmitting, receiver reporting no signal).

Can somebody who is familiar with the specifics of the UT systems tell me whether actors using phones could have contributed to this? Doesn't sound likely - but anybody else who may have a reason for this strange problem is VERY welcome to contribute!).
 

Chris15

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Jul 15, 2005
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I seem to recall something about there needing to be a degree of separation between transmitter and receiver. Maybe the transmitter & receiver were too close to one another? Are there frequency controls? Could someone have bumped one?

Sounds like an unusual problem.
 

PhantomD

Joined
Mar 3, 2006
Location
Brisbane, Australia
It is weird. The mics in question had been in use onstage and dropped out (perhaps beside a phone?), and so I had to replace them and try and figure out what was going on. One got sent for repairs.
 

fosstech

Active Member
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Jun 7, 2004
Location
Tacoma, WA USA
Yeah, Nextel phones are pretty bad. I've never had one interfere with a wireless mic, but I have had them interfere with some VHF high band communications before. Never had a problem with my Verizon phone interfering with anything.
 

mbandgeek

Active Member
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Apr 1, 2006
Location
North Carolina
I guess i count myself lucky that there are only 3 local tv stations and the mountains block most of the Tv stations from the north and south. Meaning no interference, even when running 4 or 5 units at the same time.
 
Joined
Dec 25, 2003
i have heard, not sure if this is fact, that the transmitters can overload the recievers if they are too close together. do they work if they are further away.
 

PhantomD

Joined
Mar 3, 2006
Location
Brisbane, Australia
i have heard, not sure if this is fact, that the transmitters can overload the recievers if they are too close together. do they work if they are further away.
No.

Fifty percent offtopic: can phones disrupt a lights board? I read this the other day:

yeah board may emit a miniscule amount of magnetic energy which the phone catches onto and thinks its a phone tower and tries to connect
I was the victim of a board reset the other day and I still haven't tracked it down. A mobile was under the console.
 

Chris15

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Sounds very much like a conspiracy theory to me... I would think the amount of EMR in question so tiny that it is implausible. Though I am willing to stand corrected if there is a reason why it would occur...
 

mbenonis

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Sep 1, 2003
Location
Chicago, IL
i have heard, not sure if this is fact, that the transmitters can overload the receivers if they are too close together. do they work if they are further away.
Two receivers close together can't overload the receivers, but they *can* cause intermodulation, thus possibly causing noise on other channels. If they are more than a foot or two away from each other they should work fine (unless your frequencies are poorly coordinated, in which case you're going to have problems no matter what you do).
 
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