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Thread: Mobile Phone interference on radio mics

  1. Default Mobile Phone interference on radio mics

    Hi
    I was shooting a wedding recently using a shotgun mic and Sennheiser G2 radio mics. I got a lot of mobile phone interference throughout the speeches on the radio mics. I'm based in Ireland but am still wondering if there are any particular frequencies that are less prone to mobile phone interference?
    Thanks
    Paul

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    Mobiles can be a right pain for this... I doubt there's a deal you can do - I even heard it on a live BBC news report recently - so even their gear suffers too.

    Rembrandt Rob is the man who'll know if there is a solution... but I doubt there is one other than trying to keep packs a yard or more away from mobiles.

  3. Default

    That's not a bad idea to try and keep a good distance between the packs and mobiles.
    Cheers

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    Mobiles are a right pain and there's very little you can do.

    Distance helps. The further you keep mobiles away from transmitters and receivers the better. Sound technicians are the worst offenders! They put their mobile on "silent" or "flightsafe" (a freelancer NEVER turns off his mobile), place it on top of the rack and then are surprised when they get the da-da-dit-dit-didaa coming through loud and clear.

    What happens is that the mobiles regularly send out a signal, even if you're not telephoning. This 'search" signal is a lot stronger than a normal telephone signal as it's required to find the nearest base station. This signal gets "picked up" by the radio-mic's carrier wave and added to the mix. The signal is obviously on a different frequency to the radio mic but, close to the mobile, the signal and its harmonics are so strong that they can be scooped up by other signals. It can happen with wires too, but is very rare and almost unheard of with shielded cables unless you actually place the mobile in contact with the wire.
    On the receiver end, if the mobile's close enough, those same harmonics are strong enough to be picked up and converted into a signal.

    There are urban-myth solutions like don't have the mobile parallel to the transmitter/receiver but at right angles, or make sure there's metal between them but the only solution I found was distance. My regular soundie still bitches about "the devil's boxes" so it would appear that the latest 'phones are still causing problems.

    The best solution is to have the radio bridge as short as possible. ie, as little distance between the transmitter and receiver as you can get. On a set, for example, have the receiver just out of frame on a c-stand. On stage, have it in the wings or right at the edge of the stage (though not resting on a speaker or anything elctric or electronic) and run the rest of the way with a wire. Have the transmitter cranked up to maximal signal and the transmitter cranked down to minimum. If you can adjust the "squelch" have it cranked right the way up so that the mic signal only just opens the gate.

    Most importantly though, turn off your mobile when you're on a job.

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    Smile

    Quote Originally Posted by Rembrandt Rob View Post
    ...Have the transmitter cranked up to maximal signal and the transmitter cranked down to minimum....
    Rob... can you claify?

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    Yeah, some transmitters have a power setting, sometimes a two position switch high/low. The idea being that you use the minimum power necessary so that others can use the same frequency more than a few hundred yards away without clashing. Stuff it!. If you're getting interference, put your transmitter on max.
    The receiver also has a filter, a sort of sensitivity control so that you can make the receiver very sensitive, used if your transmitter is a long way away, or less sensitive. Often pre-set but some are adjustable. By having it at the less sensitive setting, only strong signals will be received which is why you have the transmitter on maximum.

    Think of it as shouting loudly at someone with cotton wool in their ears. The only thing they will hear is the person shouting as everything else is filtered out.

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    Go back and read the quote mate..... transmitter and transmitter cranked up and down.....

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    Oh balls!

    Quite right, I meant to say transmitter cranked to the maximum output and receiver on the least sensitive setting.

    It's the alzheimers mate!

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    Thanks very much for the info. I'm going to sound like a spanner here but, are mobiles on flight safe still a problem?

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    In theory they shouldn't cause a problem. The "Flight-safe" mode stops them from constantly seeking out the nearest base station and changes them into a "receive only" mode... theoretically.

    Personally, for the duration of the job I would suggest that you turn off all mobiles within your sphere of control (ie the crew).

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