How to keep iPhone from picking up an unwanted radio signal

Question

Level 1

116 points

How to keep iPhone from picking up an unwanted radio signal

The iPhone appears to be picking up a radio station. I believe that it is the phone because I don't hear the station when (a) I only have the headphones on, or (b) when I have the headphones on and the headset cable is attached to the headphones (but not to the iPhone).

As soon as I attach the headphone cable to the iPhone I hear the radio station. It doesn't matter whether I am listening to the iPod music or, in fact, have any app running. I even hear music when the iPhone is "off" (standby). I hear music until I hard power down the iPhone. Then, when I turn it back on, as soon as I see the 'apple' (before the system is fully up) I start hearing the music. I have tried two headphone sets -- one with a noise-cancelling feature and the others just cheap old headphones. No difference.

I have tried turning off WiFi, even putting the phone in "airplane" mode. So far, nothing works.

Any ideas on how to block the unwanted music? I want to use the headphones outside (to block roadwork on the street below) but obviously this is not feasible since the annoying, secondary music is playing in the background. It is almost worse than the city's ditch-digging equipment!

2nd Gen iPhone, iPhone OS 3.1.2

Posted on Dec 30, 2009 1:22 PM

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Answer 1

keriah Author

Level 1

116 points

Jan 3, 2010 9:40 AM in response to Denis247

Denis247 wrote:
...If very annoying, it would be possible to fit a simple radio-frequency filter to the headphone lead to prevent these signals being fed back into the ipod and being 'processed'.
As a first effort, try wrapping the plug end of the lead around a ferrite bead, similar to that 'lump' you find on leads such as usb cables etc.

It took some time to locate the little black 'bead' (from our years-ago futile attempts to block that ghosting TV signal) but when we did it worked like a charm! Since it is designed to surround a thicker (TV) cable, we wrapped the headphone cord around it three times before snapping it shut (which also keeps it from slipping down the cord). It blocks the radio signal, even on the Shuffle (where the interference was strongest). Thanks for the explanation and tip.

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Answer 2

Denis247

Level 1

85 points

Dec 31, 2009 10:37 AM in response to keriah

Most probably the headphone cable acting as an antenna is feeding the radio frequency signal to the audio circuit in the iphone/pod which is demodulating it and outputting it as an audio signal back to the headphones. The other player would have different audio circuitry which explains the different response.

I doubt whether the rf signal on it's own would be able to reproduce the audio without the effect of the ipod's audio circuitry to demodulate and amplify it.

If very annoying, it would be possible to fit a simple radio-frequency filter to the headphone lead to prevent these signals being fed back into the ipod and being 'processed'.
As a first effort, try wrapping the plug end of the lead around a ferrite bead, similar to that 'lump' you find on leads such as usb cables etc.

Message was edited by: Denis247

Message was edited by: Denis247

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Answer 3

wjosten

Level 10

95,369 points

Dec 30, 2009 2:16 PM in response to keriah

If you put the phone in airplane mode, with both bluetooth & wifi turned off(they be be turned on in airplane mode through settings), then all radio chips are off. Perhaps your headphone cable is acting like an antenna if the signal is strong enough.

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Answer 4

keriah Author

Level 1

116 points

Dec 31, 2009 10:07 AM in response to Tamara

Tamara wrote:
I don't have an answer but you're the first person to ever report this happening in these forums in the 2 1/2 years the iPhone has been around.

Lucky us, eh!

FWIW, this isn't the first experience with unwanted signals. We are on the 44th floor in a dense urban area. We are line of sight with several radio and TV towers.

Before the DTV transition we had an annoying TV signal that 'ghosted' over a particular cable channel. For over a decade we tried everything to get rid of it -- we were told that the boxes were acting as receivers, that the wires were acting as receivers, and finally that the entire living room (wiring in the walls) was acting as receiver.

This morning I determined that our iphone-radio signal is 94.7 -- I just wish they had a more interesting broadcast.

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Answer 5

keriah Author

Level 1

116 points

Dec 31, 2009 10:14 AM in response to wjosten

wjosten wrote:
If you put the phone in airplane mode, with both bluetooth & wifi turned off(they be be turned on in airplane mode through settings), then all radio chips are off. Perhaps your headphone cable is acting like an antenna if the signal is strong enough.

Good thing we have plenty of devices for testing. I tried again with both iPhones (1st and 2nd gen.) -- Bluetooth is already off and putting it into Airplane mode didn't make a difference. Then I tried the Shuffle -- it received an even stronger version of the broadcast.

Yes, I would begin to suspect the headphone wire, except that when my husband (same location on the lanai) plugged the headphones into his MBPro and listened to a CD he didn't pick up the radio station signal.

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Answer 6

Tamara

Level 6

13,744 points

Dec 30, 2009 2:11 PM in response to keriah

I don't have an answer but you're the first person to ever report this happening in these forums in the 2 1/2 years the iPhone has been around.

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