# headphone wires as antennas? **URL:** \ **Category:** Factual Questions\ **Created:** [August 14, 2014, 8:23pm UTC](https://boards.straightdope.com/t/headphone-wires-as-antennas/695541 "2014-08-14T20:23:36Z")\ **Posts on this page:** 19\ **Page:** 1
**Author:** ![EdwinAmi](https://avatars.discourse-cdn.com/v4/letter/e/5fc32e/32.png) [@EdwinAmi](https://boards.straightdope.com/u/EdwinAmi)\ **Post date:** [August 14, 2014, 8:23pm UTC](https://boards.straightdope.com/t/headphone-wires-as-antennas/695541/1 "2014-08-14T20:23:36Z")
So, being an awkwardly old-fashioned guy for someone who grew up with computers and programming, I kept using the iPod my little brother got me for Christmas like 10 years ago. Had the moving hard drive and everything. Finally, it conked out on me, so I bought an iPod nano. I was surprised to find the thing can pick up radio. Then it says the headphones need to be plugged in for it to work. Clearly they’re using the headphone wires as the antenna. But how can this be? Doesn’t the much stronger electric signal going up to the headphones mess with receiving the radio signals? Can a wire that’s conducting like 5 volts of eletcrity and .2 amps or whatever it is even pick up radio waves in the first place? Do the signals get picked up anyway, and just slightly modify electricity that’s going up/down the wire, and so the iPod just filters that out? I know there must be some kind of filter in general. Is it an electronic filter, or does it use the computer of the iPod to do it algorithmically? What the dilly, yo? ---
**Author:** ![GaryM](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/garym/32/241_2.png) [@GaryM](https://boards.straightdope.com/u/GaryM)\ **Post date:** [August 14, 2014, 8:32pm UTC](https://boards.straightdope.com/t/headphone-wires-as-antennas/695541/2 "2014-08-14T20:32:17Z")
Think about your phone line carrying your conversation with a friend and your son’s dsl data as he games with his online friends. ---
**Author:** ![engineer\_comp\_geek](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/engineer_comp_geek/32/504_2.png) [@engineer\_comp\_geek](https://boards.straightdope.com/u/engineer_comp_geek)\ **Post date:** [August 14, 2014, 8:37pm UTC](https://boards.straightdope.com/t/headphone-wires-as-antennas/695541/3 "2014-08-14T20:37:44Z")
One of the first things they teach you in EE school is how easy it is to make a radio receiver. Then you spend a lot of time learning how to make all of your circuits NOT be radio receivers. If you don’t very carefully design your iPod (or whatever else you are designing) then radio noise from the headphone wires can easily end up all over the place in your circuits. A good example of this is computer speakers. Most computer speakers these days (except for the really small and cheap ones) have an amplifier in the speakers and don’t rely on the (usually smaller) amplifier that is built into the sound card. Place a cell phone next to your speakers, and your speakers will “chirp” periodically, and will get very chirpy just before a call comes in (as the phone and the tower talk to each other, setting up the call). The reason the speakers chirp is that radio noise from the cell phone gets picked up by the speaker wires and gets coupled into the speaker’s circuitry, resulting in unwanted noise in the speakers. It’s fairly easy to make a high pass circuit that only passes radio frequency energy into the radio receiver part of the iPod while rejecting all of the much lower audio frequency stuff that is going up to the headphones. It’s a bit of a challenge to make these kinds of circuits fit into the size of an iPod, but overall it’s not that difficult compared to other things these days. ---
**Author:** ![iljitsch](https://avatars.discourse-cdn.com/v4/letter/i/77aa72/32.png) [@iljitsch](https://boards.straightdope.com/u/iljitsch)\ **Post date:** [August 14, 2014, 8:40pm UTC](https://boards.straightdope.com/t/headphone-wires-as-antennas/695541/4 "2014-08-14T20:40:39Z")
Phone/DSL: Not the same thing, as those are both high power. FM frequencies (~ 100 MHz) and audio (~ 10 kHz) are so far apart that they really don’t get in each other’s way. I’m also pretty sure they only use the ground wire as the antenna, further reducing the problem. The radio needs to be tuned to a specific frequency to pick up a specific station, even if another station is only 200 kHz away. The audio 99.99 MHz away then really isn’t a problem for the filter, even though it may be quite strong. What I never understood is how some two-way radio systems presumably send and receive at the same time using the same antenna. Or are they actually using time devision multiplexing, so the sending and receiving alternate? ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [August 14, 2014, 9:01pm UTC](https://boards.straightdope.com/t/headphone-wires-as-antennas/695541/5 "2014-08-14T21:01:22Z")
Note that this method of using the headphone wire as an antenna is nothing new. Walkmans (remember those?) with an included radio did the same thing. ---
**Author:** ![johnpost](https://avatars.discourse-cdn.com/v4/letter/j/f17d59/32.png) [@johnpost](https://boards.straightdope.com/u/johnpost)\ **Post date:** [August 14, 2014, 9:11pm UTC](https://boards.straightdope.com/t/headphone-wires-as-antennas/695541/6 "2014-08-14T21:11:34Z")
everything metal is an antenna. tuning circuitry filters out (hopefully) all but the desired signal. ---
**Author:** ![EdwinAmi](https://avatars.discourse-cdn.com/v4/letter/e/5fc32e/32.png) [@EdwinAmi](https://boards.straightdope.com/u/EdwinAmi)\ **Post date:** [August 14, 2014, 10:56pm UTC](https://boards.straightdope.com/t/headphone-wires-as-antennas/695541/7 "2014-08-14T22:56:37Z")
> [@](#): > > Think about your phone line carrying your conversation with a friend and your son’s dsl data as he games with his online friends. Good point. I should have thought of that ---
**Author:** ![EdwinAmi](https://avatars.discourse-cdn.com/v4/letter/e/5fc32e/32.png) [@EdwinAmi](https://boards.straightdope.com/u/EdwinAmi)\ **Post date:** [August 14, 2014, 11:01pm UTC](https://boards.straightdope.com/t/headphone-wires-as-antennas/695541/8 "2014-08-14T23:01:22Z")
OK, so here’s a related question I’ve always wondered about. I’ve seen those pictures where they show one fiber optic line, and it can transfer the data of a also-shown giant bundle of copper cables. From what I understand about fiber optics, all data is transmitted by flashing on and off. And what I was told is that it’s (apparently) easier to make a machine that can see a bajillion flashes per second and interpret them… well apparently this capability with these interpreters is so high as to replace the classic copper cables that carry/carried the audio signals. What the hell did old phone lines carry? My understanding is it was just a typical AC audio signal from the phone… So I guess the same principle applied to phones, that is one wire can carry multiple signals? But apparently there’s a limit due to interference when you have too many signals? In that case, how did bigger cables help cary more signals? Or was that just a bunch of cables wrapped together? ---
**Author:** ![beowulff](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/beowulff/32/542_2.png) [@beowulff](https://boards.straightdope.com/u/beowulff)\ **Post date:** [August 14, 2014, 11:06pm UTC](https://boards.straightdope.com/t/headphone-wires-as-antennas/695541/9 "2014-08-14T23:06:57Z")
> [@EdwinAmi](#): > > OK, so here’s a related question I’ve always wondered about. I’ve seen those pictures where they show one fiber optic line, and it can transfer the data of a also-shown giant bundle of copper cables. > > From what I understand about fiber optics, all data is transmitted by flashing on and off. > > And what I was told is that it’s (apparently) easier to make a machine that can see a bajillion flashes per second and interpret them… well apparently this capability with these interpreters is so high as to replace the classic copper cables that carry/carried the audio signals. > What the hell did old phone lines carry? My understanding is it was just a typical AC audio signal from the phone… So I guess the same principle applied to phones, that is one wire can carry multiple signals? But apparently there’s a limit due to interference when you have too many signals? In that case, how did bigger cables help cary more signals? Or was that just a bunch of cables wrapped together? Oh, so you are asking for the history of telephony in a paragraph? 😃 Originally, there was only one conversion/line. That required a lot of switched circuits, and a lot of wires. Pretty quickly, it was discovered that there is a lot of dead air in voice, and if you chop the sound up fast enough, you can _multiplex_ several conversions onto one wire. When things went digital, that became much easier, since now you could buffer the data, and do all kinds of neat compressions on it to reduce the amount of data that had to be transmitted. ---
**Author:** ![EdwinAmi](https://avatars.discourse-cdn.com/v4/letter/e/5fc32e/32.png) [@EdwinAmi](https://boards.straightdope.com/u/EdwinAmi)\ **Post date:** [August 14, 2014, 11:16pm UTC](https://boards.straightdope.com/t/headphone-wires-as-antennas/695541/10 "2014-08-14T23:16:58Z")
> [@](#): > > Pretty quickly, it was discovered that there is a lot of dead air in voice, and if you chop the sound up fast enough, you can multiplex several conversions onto one wire ohhhhh, is THAT what they do!? That’s so clever but also simple! Ohhhhhhh! I feel like an idiot. Again, I should have figured it. OK, OK, I’m less dumb now, thank you. That shit was annoying. I usually freaking know everything but that was one simple tech I didn’t know about ---
**Author:** ![Saint\_Cad](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/saint_cad/32/18907_2.png) [@Saint\_Cad](https://boards.straightdope.com/u/Saint_Cad)\ **Post date:** [August 14, 2014, 11:17pm UTC](https://boards.straightdope.com/t/headphone-wires-as-antennas/695541/11 "2014-08-14T23:17:00Z")
To add to beowulff Telephone lines carried information at the same frequency as the sound. That is why various tones (or when pushing a number, # or \* two tones are used) were used to transfer information (in-band). It wasn’t until recent that the idea that copper could transmit frequencies outside of the aural range could be used to allow for out-of-band signaling and DSL. ---
**Author:** ![beowulff](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/beowulff/32/542_2.png) [@beowulff](https://boards.straightdope.com/u/beowulff)\ **Post date:** [August 14, 2014, 11:20pm UTC](https://boards.straightdope.com/t/headphone-wires-as-antennas/695541/12 "2014-08-14T23:20:16Z")
> [@iljitsch](#): > > Phone/DSL: Not the same thing, as those are both high power. > > FM frequencies (~ 100 MHz) and audio (~ 10 kHz) are so far apart that they really don’t get in each other’s way. I’m also pretty sure they only use the ground wire as the antenna, further reducing the problem. > > The radio needs to be tuned to a specific frequency to pick up a specific station, even if another station is only 200 kHz away. The audio 99.99 MHz away then really isn’t a problem for the filter, even though it may be quite strong. > > What I never understood is how some two-way radio systems presumably send and receive at the same time using the same antenna. Or are they actually using time devision multiplexing, so the sending and receiving alternate? Most radios that use the same antenna for transmit / receive use a special [switch](http://www.cel.com/pdf/brochures/rf_switch_ic_web.pdf) to switch the antenna from the power amplifier to the low-noise amplifier. This means that the transceiver can’t transmit and receive at the same time - which is generally not a problem, since most systems spend the majority of their time listening. ---
**Author:** ![tanstaafl](https://avatars.discourse-cdn.com/v4/letter/t/ba8739/32.png) [@tanstaafl](https://boards.straightdope.com/u/tanstaafl)\ **Post date:** [August 15, 2014, 11:56am UTC](https://boards.straightdope.com/t/headphone-wires-as-antennas/695541/13 "2014-08-15T11:56:45Z")
> [@EdwinAmi](#): > > ohhhhh, is THAT what they do!? That’s so clever but also simple! Ohhhhhhh! I feel like an idiot. Again, I should have figured it. > > OK, OK, I’m less dumb now, thank you. That shit was annoying. I usually freaking know everything but that was one simple tech I didn’t know about That is also why at one time you got “ghost conversations” on calls; especially long distance ones. You could be talking to someone and faintly hear someone else talking as well. You were getting overlap between your reassembled conversation and someone else’s. Modern digital circuits have pretty much eliminated that now. ---
**Author:** ![allyn](https://avatars.discourse-cdn.com/v4/letter/a/ec9cab/32.png) [@allyn](https://boards.straightdope.com/u/allyn)\ **Post date:** [August 15, 2014, 7:04pm UTC](https://boards.straightdope.com/t/headphone-wires-as-antennas/695541/14 "2014-08-15T19:04:53Z")
\ If the requirement is to receive a signal on an input frequency and rebroadcast it on a different output frequency (e.g. a radio repeater) then you would use a “Duplexer” [http://en.wikipedia.org/wiki/Duplexer](http://en.wikipedia.org/wiki/Duplexer) \ ---
**Author:** ![engineer\_comp\_geek](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/engineer_comp_geek/32/504_2.png) [@engineer\_comp\_geek](https://boards.straightdope.com/u/engineer_comp_geek)\ **Post date:** [August 15, 2014, 7:39pm UTC](https://boards.straightdope.com/t/headphone-wires-as-antennas/695541/15 "2014-08-15T19:39:13Z")
\ You don’t usually see them on things like handheld radios, but there’s a thing called an RF circulator that you can use to allow you to transmit and receive on the same antenna at the same time, and on the same frequencies. Basically, the outgoing RF signal goes out through one port and to the antenna, and incoming signals from the antenna go to a third port instead of going to the first port (the first port being the one where the outgoing signal came from). > **[Circulator](https://en.wikipedia.org/wiki/Circulator)** > > In electrical engineering, a circulator is a passive, non-reciprocal three- or four-port device that only allows a microwave or radio-frequency signal to exit through the port directly after the one it entered. Optical circulators have similar behavior. Ports are where an external waveguide or transmission line, such as a microstrip line or a coaxial cable, connects to the device. For a three-port circulator, a signal applied to port 1 only comes out of port 2; a signal applied to port 2 only com... \ ---
**Author:** ![JWT\_Kottekoe](https://avatars.discourse-cdn.com/v4/letter/j/3ec8ea/32.png) [@JWT\_Kottekoe](https://boards.straightdope.com/u/JWT_Kottekoe)\ **Post date:** [August 16, 2014, 2:12am UTC](https://boards.straightdope.com/t/headphone-wires-as-antennas/695541/16 "2014-08-16T02:12:21Z")
[hijack] Yes, and a circulator is a non-reciprocal device. It allows the signals to propagate between the three terminals in a clockwise direction but not in a counterclockwise direction. On first blush, this seems to a physicist as a violation of the left/right (parity) symmetry of the laws of electromagnetism, but there is a trick. Can you guess what it is? A magnetic field applied to a non-reciprocal material breaks the symmetry [/hijack] ---
**Author:** ![GaryM](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/garym/32/241_2.png) [@GaryM](https://boards.straightdope.com/u/GaryM)\ **Post date:** [August 16, 2014, 2:18am UTC](https://boards.straightdope.com/t/headphone-wires-as-antennas/695541/17 "2014-08-16T02:18:43Z")
> [@iljitsch](#): > > Phone/DSL: Not the same thing, as those are both high power. I know that. I was just illustrating that one piece of wire was carrying two or more signals at the same time without them interfering with each other. ---
**Author:** ![TBG](https://avatars.discourse-cdn.com/v4/letter/t/c89c15/32.png) [@TBG](https://boards.straightdope.com/u/TBG)\ **Post date:** [August 17, 2014, 2:17am UTC](https://boards.straightdope.com/t/headphone-wires-as-antennas/695541/18 "2014-08-17T02:17:31Z")
> [@Chronos](#): > > Note that this method of using the headphone wire as an antenna is nothing new. Walkmans (remember those?) with an included radio did the same thing. Only for FM, though, AM was handled by some sort of internal antenna. Or so the Walkman[sup][sup]TM[/sup][/sup] brand personal stereo documentation claimed. ---
**Author:** ![johnpost](https://avatars.discourse-cdn.com/v4/letter/j/f17d59/32.png) [@johnpost](https://boards.straightdope.com/u/johnpost)\ **Post date:** [August 17, 2014, 2:52am UTC](https://boards.straightdope.com/t/headphone-wires-as-antennas/695541/19 "2014-08-17T02:52:22Z")
AM needs a longer antenna than FM. pocket radios use a coiled antenna for AM.