Mobile Phone Interference

[PurPleY11]

Hi All

 

I a conferencing and events technician and sometimes I have had intermittent mobile phone interference (that horrible noise that you cant help but cringing at)

I have read on a few forums that it could be down to GSM networked handsets but this seems quite a vague answer as why with the advancement in microphone and speaker cabinet design would this still be a problem?

Personally I have always put it down to poorly shielded microphone capsules as it only seems to happen when using the Shure MX412 goosenecks that the company that I work for uses. but today I had that problem on a wireless Shure ULX handheld. This has never happened before on ANY wireless product ive used (and I use these handhelds day in and day out!!)

 

Now I know one solution would be to ask all the delegates to turn off their mobile devices but you ask any corporate client to turn off their blackberry and they'll look at you like you've walked on stage and exposed yourself

 

Does anyone have any pearls of wisdom?

 

Thanks in advance

Tom

[chelgrian]

I a conferencing and events technician and sometimes I have had intermittent mobile phone interference (that horrible noise that you cant help but cringing at)

I have read on a few forums that it could be down to GSM networked handsets but this seems quite a vague answer as why with the advancement in microphone and speaker cabinet design would this still be a problem?

Personally I have always put it down to poorly shielded microphone capsules as it only seems to happen when using the Shure MX412 goosenecks that the company that I work for uses. but today I had that problem on a wireless Shure ULX handheld. This has never happened before on ANY wireless product ive used (and I use these handhelds day in and day out!!)

 

It's fundamentally hard to keep out a 900MHz or 2.1GHz signal that could be transmitting at anything up to 2W.

 

However to induce enough signal to get interference the phone would need to be quite close to the single ended bit of the chain, the mic capsule. More than a couple of feet away and it's unlikely you'll get a problem unless the mic is badly designed.

 

Is it possible that there is a phone anywhere near the mixer which is inducing a signal inside the mixing desk itself? Are there any unbalanced connections going in to the mixer which could have a phone anywhere near them?

 

The line you have to use with the mic users is 'if you don't turn your phone off then the audience may not be able to hear you or may be distracted from your talk/presentation whatever so its in *your* interest to make sure that it's completely off'.

[azlan]

Re the wireless one, what frequencies are using, afaik the ulx gear we have can tune into some of the mobile phone spectrum?

 

Ch38 is only really covered in groups 7 and 8 on them

[Shez]

Re the wireless one, what frequencies are using, afaik the ulx gear we have can tune into some of the mobile phone spectrum?

I'd be very surprised if you could legally use the same spectrum that the mobile phone companies have paid millions to use.

[laolu]

I was already wondering out loud (also in this forum) why a hand-phone creates interference with VHF, but not with UHF radio mics? No idea. Logic would suggest it is the other way round, no? :blink:

 

Norbert

[paulears]

Sennheiser explained that much of the problem comes from the fact that filtering on mobile phones to keep their output in their band, gets cut once phones are in production, making the ones in use quite different from the ones tested. They had been looking at 4g phones that had measurable output in ch 70. You hear mobile interference everywhere, and stopping it is difficult. The fact they try so hard to get you to turn them off on a plane shows that it's out of band problems they're worried about, not it's supposed operating frequencies.

[Andrew Edwards]

I have noticed that the latest generation smart phones from various manufacturers do not seem to exhibit as much but it also seems to depend on the network.

 

The iPhone 5s (on Three or EE) does not cause anything on my el cheapo pc speakers in the office, even right up close on a call. Yet if someone comes up to the front desk (about 3m away) I can get interference from whatever phone they have. A 4s on 02 is horrendous for it too.

 

OT

I watched an old aircrach investigation last week where mobile phone was a potential cause as the familiar noise was heard on the CVR. It was a crash from the early 90s and it turned out not to be the case but only after flying about in a similar plane with various mobile phones on. If nothing else, keeping the CVR (or comms for that matter) clean is a good enough reason to not allow phones on a flight.