Hear some occasional buzzing in your ANR headset? Check your Iphone..

I was getting some occasional buzzing while sitting on the ground in my new Zulu headset. It was driving me crazy since I could not tell where it was comming from. I never heard it in the air. I thought I had a bad headset.

Tonight I heard the same thing (same buzz same pattern) over my computer speakers and it turns out it is my Iphone in my pocket causing the buzz...

The Iphone puts out some nasty RF that must have a harmonic in the audible range!!! It only does this occasionally like when it is syncing mail or something similar.

Every digital cell phone I've ever had did this. I don't think it has anything to do with the I-Phone in particular.
It does this when it is searching for a tower.

Switching to airplane mode is now part of my preflight checklist. I too thought I had some big-time electrical problems until I realized it was my phone causing the problem you describe.

Cell Phone Interference

Make that "Darn", it happens to my car radio too....lol. Let's all just get SAT phones.

Something I've noticed, is that cell phones of a certain network type (ATT, T Mobile on the GSM network) make that noise, but Sprint and Verizon (on CDMA network) do not. I have sprint and I never make noise near sound equipment

Another reason to turn it to "Airplane mode" is to save battery life. If your flying where you can't get a cell signal the phone will continually try to find a cell tower. And in the process it will help drain your battery.

I've heard the same thing with my iPhone/Zulu combination. I've felt it was more apparent with the bluetooth on, but in thinking back, I heard the same thing via my truck speakers, pre-iPhone and no bluetooth (all ATT though).

Brian or others with iPhone/Zulu...does the noise seem to correlate to bluetooth on/off at all in your experience?

Interesting that CDMA phones don't do this...hmmmm.

Thanks for the info!!

Cheers,
Bob

fm_weasel said:

Something I've noticed, is that cell phones of a certain network type (ATT, T Mobile on the GSM network) make that noise, but Sprint and Verizon (on CDMA network) do not. I have sprint and I never make noise near sound equipment

Click to expand...

All GSM based phones (850/900/1800 Mhz) will cause audio interference which occurs when the phone is moving between towers, or when the phone is actively transmitting data - e.g. checking for mail, etc.

CDMA based phones operate in different frequency ranges, and do not exhibit this behaviour.

We have to be very careful with what SIM cards our customers put into sat/cell dual mode tracking units, otherwise it becomes unusable due noise in the headsets. Repeated, albeit anecdotal, advice from our customers is that GSM phones are much noisier and less "friendly" to avionics than CDMA, and are designed with distance filtering which results in more tower hopping and less range. I'm sure that there will be more qualified people than I here who can talk with more authority than I can on this.

new iphone... silence on the airwaves

just another data point... i recently replaced my first generation iphone with the new 4th generation unit and noticed immediately silence on the airwaves with the phone on the nightstand next to the radio. my first gen unit would click and tick over just about any nearby speakerphone or radio whenever it transmitted; it would need to be at least 4-5 feet away to keep quiet. in the plane the rf transmitted from the old phone was terrible.

the new iphone is completely silent everywhere i have tested it...

Unfortunately, you guys with newer iPhones will still get the GSM buzz as soon as the phone loses 3G and falls back into Edge data mode.

Boring facts:
It has nothing to do with the radio carrier frequency (800MHz, 1800MHz, etc) but is related to the 'packet transmission frequency'. That is, it only sends a burst of data every so often, and it just happens to do that at regular intervals about 218 times a second. It's that 218Hz tone that is audible.
There are two useful implications of this:
One is that it requires an active element to be audible.

Bare headphones -> no sound. Headphones plugged into a radio or amplifier -> buzz. This is due to the headphone wire picking up the radio signal as an antenna, conducting it to the active elements in the amplifier, the amplifier converting it in a way similar to an AM radio, and sending it back to the headphones as audio buzz.

The second is that it is possible to design electronics that reject the carrier frequency OR the audio frequency, or both.

The carrier frequency can be very difficult to filter, depending on how close it is to the active electronics. In this specific instance, it sounds like the phone is inducing the ANR circuit in the headset to buzz. I have also seen a PS Engineering intercom pick up the buzz with regular headsets, when the headset cord runs by my pocket.

There are a few things I'd recommend in your case:
Move the phone away from your headset wiring
Turn the phone off (obviously)
If those aren't options, you can experiment with snap-on ferrite EMI supressors:
http://mouser.com/Passive-Component...-RFI-Suppressors-Ferrites/_/N-194jj?P=1yzv8sh
That link should show you only the snap-on type. Try to find one that matches your cable diameter (the ID or inner dimension of the ferrite should be close to the cable you're snapping it on).
Put them between where interference might be getting in (long lengths of wire) and active elements. So, something I might start with, is headset-ferrite-cable-ferrite-jack, with the ferrite placed close to the active element it is protecting.
There is no guarantee to this approach, but it might do what you want.

Hi Daniel

Thanks so much for the correction and clear explanation - boring facts indeed! I now know something I didn't yesterday. I love this forum!

Cheers
Chris