How Can Headphones Act as Antennas

  • Thread starter peter.ell
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  • #1
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If you've used Apple's latest iPods, you know that they feature a built-in radio that uses the headphones themselves as an antenna. But how is this possible?

I really have two questions about this:

1.) Aren't the headphone wires shielded and insulated so that they should not be able to pick up radio waves?

2.) If the insulation has little affect, then this means that radio waves passing through the headphone wires induce currents in the wires that match the radio waves, right? But then this must happen all the time, not just when I select the radio app on my iPod, right? So then how can radio waves all around us be constantly inducing currents in headphone wires without those currents interfering or distorting the audio signals already traveling within them?

Thank you so much!
 

Answers and Replies

  • #2
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If you've used Apple's latest iPods, you know that they feature a built-in radio that uses the headphones themselves as an antenna. But how is this possible?

I really have two questions about this:

1.) Aren't the headphone wires shielded and insulated so that they should not be able to pick up radio waves?

2.) If the insulation has little affect, then this means that radio waves passing through the headphone wires induce currents in the wires that match the radio waves, right? But then this must happen all the time, not just when I select the radio app on my iPod, right? So then how can radio waves all around us be constantly inducing currents in headphone wires without those currents interfering or distorting the audio signals already traveling within them?

Thank you so much!
1. I expect that the shield is used as the antenna. The shield is not connected to ground, therefore it can receive radio signals.

2. The frequency of the RF signals are much higher than the audio range so we can't hear them.

Besides, the headphones would not operate at those frequencies either.
 
  • #3
The person in question might not be around, but still.
2. The frequency of the RF signals are much higher than the audio range so we can't hear them.
RF signals are EM waves, not longitudinal waves like sound!
 
  • #4
berkeman
Mentor
58,023
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RF signals are EM waves, not longitudinal waves like sound!
He was referring to the frequency difference between RF and audio, not the modality of the wave propagation.

EDIT -- Also, the audio signals in the iPod and in the headphone wires are indeed electrical signals, not in-air sound waves.
 

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