Some family members of mine were in bed in their house during a thunderstorm and during a close lightning strike they heard a few seconds of music that sounded like a radio transmission, somehow being amplified throughout throughout the house as the lightning flashed. I believe their story, and wonder about the mechanism.
I had a lightening strike relatively near to me once (I.e. hundreds of metres rather than miles away) and just as it halterneck there was such a strong electro-magnetic field that the air felt "chewy". There was resistance in opening and closing my mouth.
>I found out that the radio station's wavelength she was listening to was about 3.3 meters
That's 90MHz, which is in the FM band (at least in the USA). I understand (and have experienced) how this works with AM, but how does this work with FM? Does some circuitry in the headphone act as an FM decoder?
My best guess would be that slope detection could be converting the FM signal into AM. This happens in circuits where the response is strongly dependent on frequency (see [1]). A specifically designed filter is typically used, but a resonant circuit like the headphone wires could do something similar. But then you still need to get from AM to audible, and to do that you still need some sort of non-linearity in the system. Some possibility non-linearies could be a poor connection resulting in a whisker-style rectifier junction, or perhaps a magnetic permeability non-linearity in the headphone speakers. I'm sure there are others.
Related, but probably not relevant: Stereo FM broadcast signals in most parts (all parts?) of the world also contain an AM subcarrier. The primary FM carrier has the L+R audio content and is used by both monaural and stereo receivers. Stereo receivers make use of an additional AM modulated sub-carrier (+/- 38 kHz from primary carrier) to obtain L-R audio content. I don't believe this AM carrier is directly rectifiable because it does not manifest as envelope modulation in the full signal.
I experienced this just last month! Except, I didn't know it at the moment. I was participating in a design review while wfh on meet. We were having some good discussions, which I participated in. Partway through the meeting I start to fidget a bit and unplug my mic, untwist it from my headphone cable and plug it back in. Next time I unmute, unbeknownst to me, everyone else starts hearing the local radio station. I was using a schiit fulla DAC, and one of its features is auto gain on the microphone. Well I apparently didn't plug the mic in enough and it picked up the local radio station and then boosted the gain enough that it came through loud and clear over the call. Blew my mind once I learned wtf was going on. Embarrassing in the moment as I was muted twice and told to stop listening to a podcast during the meeting.
What's interesting to me is that one particular station came in clearly, given how the difference in broadcast FM allocated frequencies translates into millimeters of antenna length. (e.g. 98.3 vs 98.7 MHz = 3051mm vs. 3039mm)
Just some flexing / coiling of the cord could mean you would favor a different station or get tons of mixing in of other stations.
Maybe the key is that the author / friend was very close to a broadcasting antenna and that overwhelmed any other station that would equally have been received on the headphone cord otherwise?
regardless of the veracity, the author was not speaking of the cord lentgh, but the length of the tiny coil of magnet wire attached to the diaphragm inside the ear-phone.
... no he's not. The length of the wire has no relevance to radio reception, and I don't think it's implied that the classmate permitted the author to dismantle her headphones. He coiled the wire round a bottle to determine its overall length... which is something you could do easily and nondestructively to the headphone lead without incurring the wrath of a classmate.
You could certainly be right, as there is no guarantee the measurement was made in a sane way.
The reason I concluded he was talking about the diaphragm coil wire is as follows: it would seem a lot simpler to measure the cord length by a simple ruler, whereas precisely as not to destroy the diaphragm coil one may be tempted to estimate that length by counting the number of loops and measuring the diameter...
Anyway, the story reads very apocryphal because there are no pictures, its unclear language, and the implication of unintentional FM reception is rather ... hard to fathom.
> Don't get discouraged by people being a bit condescending, it's a cool discovery.
But as of this moment, my reading returns zero condescending comments. Probably everyone here at HN had the same experience.
So what exactly is lurking deep in this horror movie of a social network?
If you sort by oldest, and click to expand, you suddenly see it. First comment:
> 1.75*2 = 3.5
... with a thread of people having fun at the poster's expense.
To sum up:
* we outsiders from HN are greeted by a pleasant, avuncular top comment followed by enthusiastic discussions by the scientifically curios
* reddit OP was greeted by a terse correction followed by a peanut gallery of asshats (all of which get collapsed and swept under the rug for us outsiders)
This may seem tame, but remember this is only a benign scientific discussion.
If you follow my model here and "look under the carpet" on a post about abortion or trans people, trust me you'll never want to eat at reddit again! :)
I guess there's a bit of a negative filter for early comments on any given post: the people who respond quickly typically won't be the people who take their time to leave thoughtful comments, and the people who see the post first will be people who spend too much of their lives on Reddit.
> and the people who see the post first will be people who spend too much of their lives on Reddit
Except that every OP by default gets their inbox lit up by responses, typically unmoderated, in the order they were received.
So a person lurking casually on Reddit gets the false sense that threads are typically fun and light-hearted, enticing them to post. But the moment they do they become part of the Reddit ingroup, and their inbox gets bombarded with first-post asshat comments. Later, moderators and users downvote the asshats and the backend shuttles them away from all consequent casual lurkers.
It's like pre-digital hazing, except somehow even worse because there's no community bonding (or even community, really). Just unfortunate souls similar the poster below who said their mental health "takes a nose dive" when exposed to the nastier abusive comments/threads. Or even the unlucky lurker who wins the race against the moderators/downvoters of the abusive content. (None of whom are paid, btw. Yay!)
I might have missed something, but there's only one other person in the tree, who defends OP and asks a question about the procedure. I don't see anyone making fun or a peanut gallery. Do you have to be logged in to see some posts? This does seem very tame to me.
Those topics tend to be pretty upsetting here, frankly. Whenever I make the mistake of reading discussions related to that stuff here my mental health takes a nosedive
The pattern on HN is less nuanced. A story or thread gets a bunch of low-effort comments, possibly ones that are bigoted or conspiratorial depending on the content of the story. Then the entire story is flagged and frozen to further comments.
It's like dancing in your favorite club and suddenly having a surprising number of drunk finance bros grinding on you. But the music gets cut and lights go up. Everyone is forced to leave and re-enter, and when you are let back in, no finbros, better vibe, fun times again.
In contrast, Reddit is like seeing everyone on the dance-floor having a grand time, most of the time. So you finally get up the nerve to dance and are immediately surrounded by 10 tiny incels all trying to hump your leg. But everyone else on the dance floor reassures you to just keep dancing and that everything will return to normal when one of the unpaid bouncers gets back from lunch.
Edit: This is all made worse by the fact that Reddit, unlike HN, has a lot of incentives for people to post very personal stories. So even though Reddit mods can and do lock comments when things get too rough, that typically only happens when there's a critical mass of nastiness. Given that most stuff on the frontpage has 1000+ comments, that leaves room for dozens of abusive comments reaching the OP and only getting moderated later.
So a woman posts a story about narrowly avoiding a date rape, initially receives a few dozen personal insults to her inbox, which get modded, leaving what ultimately looks like a wall of enthusiasm and support, encouraging lurkers to post, who also get initial personal insults, and so on...
Interesting. Reminds me of how if you had a Nokia phone of the time next to computer speakers you could tell when you were about to get a call because the speakers would make a bup-bupbup bup-bupbup sound before the phone itself woke up and rang.
Indeed, in some cases all you need is an antenna, a semiconductor of almost any kind (which can be improvised) and an audio amp. In some cases, it's all-in-one. My family used to talk about a brass headboard that you could hear Morse code from, coming from the local military base.
To receive AM you just need a non linearity and the x^2 term iirc will do your rectification. So any element that electrically provides some kind of nonlinear behavior (ie is not a pure R, L, or C) should give some sort of modulation.
Calling bullshit. Semiconductors cannot be "improvised". PN junctions aren't found anywhere accidentally.
And a brass headboard isn't a crystal radio and isn't a circuit. A crystal radio needs a diode, a capacitor, a coil, a ground, an antenna, and a quartz headphone stuck in your ear. These things don't configure themselves by accident. The reason analog headphones with a long wire can do this is they have almost all of the attributes necessary to pickup AM radio. FM radio requires a vastly more complicated circuit.
One common type was made from an oxidized razor blade (rusty or flamed) with a pencil lead pressed against the blade with a safety pin. The oxide layer on the blade and the point contact of the pencil lead form a semiconductor Schottky diode and only allow current to pass in one direction.
Yep I mentioned that in a comment below, an accidental semiconductor IS possible, but that wasn't my point really. I get the arguers point though, a headboard implies accidental, I wasn't thinking of it that way. But anyway, as we've established, both improvised and accidental are possible and documented.
Certainly a brass headboard doesn't have a semiconductor in it. But that doesn't mean the story is bullshit. Just that it's not working in the way they think it is.
Heres an example of a thistle being used to convert an AM signal into audio. Granted, they are touching the plant directly to the broadcast tower, and it's outputting enough power that it starts burning and even burns the hand of the person holding the plant.
I admit, it's apocryphal. But, if there is a gap anywhere in joint in the headboard, and it oxidized, that's likely enough. Still, I believe my family. Maybe I have details wrong (likely) but it was a headboard and they heard radio from it.
in case this story is true I wonder if its diodes in the output driver? we aren't given enough information about the actual circuit that is formed. Could the ground level between Left and Right channels be shifted, due to the EMF in Left and Right earphone coil, which in turn results in a the ear-phone microphone signal between ground and mic-in ?
My wife's mother claims to have actually experienced this many years ago: AM radio from a tooth filling when driving close to a broadcast tower on a family road trip.
This happened to an engineer where I worked who had an analog phone with unshielded, untwisted cord exactly the length of the full-wave of the radio station.
It's also worth noting that lightning in the area can induce massive voltage and current impulses in long, unshielded, straight conductors.
My dad, whose dad had a radio and tv repair shop, got me a kit for making one when I was a little kid. I spend the day coiling the wire and following the instructions. When I was done and the artifact captured radio waves I was so excited! It's one of those vivid memories from childhood, a moment that put me on the path for a technology focused career.
radio is a gateway to abilities that some consider to be unnatural
(my grandpa gave me a shortwave and explained I could receive far-away signals due the radio signals bouncing off the ionosphere. It was my introduction to numbers stations, but I never found radio that interesting, when I had the internet available)
The solution isn't correct; it takes more distance to go around one loop of a spiral (at an angle to an implied cylinder) than it does to go around a cylinder in a circle perpendicular to the axis.
Bose QC 35 V1 headphones when charging and used passively connected via the headphone jack to an iPad or iPhone also being charged from the same source would pickup audible digital bus noise of the iDevice. Moving the charging sources to different ground planes would solve the problem. It would also happen if devices were being charged by different power adapters connected to the same neutral or ground. This led me to conclude it was a form of ground loop due to a lack of engineering and testing of the headphones.
I used to be able to hear my USB mouse scrolling in my headphones. It was so annoying I eventually go an external USB soundcard to try to decouple it, which worked.
It is a cool discovery but there's probably a bit more to it
The reason she can hear radio is that there's probably a minor short/oxidizing part that's closing the loop and rectifying the current. Cooper or aluminium oxides would do exactly that for example https://en.wikipedia.org/wiki/Metal_rectifier
The very first electronics circuit I ever built, an audio amplifier, turned out to be sensitive to the local AM radio station, WJOB, 1230 Khz. When I took it to school to show my teacher... the building shielded the signal, and it didn't work. 8(
Only later did I learn why it happened, and how to prevent it.
We had a ball lightning entering the house during a summer thunderstorm. It was only decades later I discovered that this was apparently a very rare event
Oh. Interesting. In the US, FM goes down to the high 80s. And while I've definitely been in AM dead zones, there's usually barely any FM stations in those places too because there is no audience.
What's the point of being ham nerds if no one cares what really happened here?
1.65m is FM (90 MHz) which as told is wrong. Can't pick up FM like this, it is NOT simple like all the AM stories.
Chrome books don't have inbuilt radio as far as I can see (Why not is a good question for another time. After the phone cartels destroyed radio on phones why doesn't Google put it in Chromebooks? Would it create awkward questions for their phone cartel department.)
They say coiling it doesn't change it -
The geometry of the cable does change the sound a little. I can't remember much, but I got the impression it got a little louder when I stretched it, although I could also hear it fine when wrapping it around in circles. Changing the geometry of the wire definetly changes the audio, even if by little
They didn't hear the FM radio logo, it's a friend who did, so that's not a trustworthy data point. OPs account seems legit, so you could probably trust their personal experiences.
It's probably either a AM re-transmission of FM or an AM station. The cord is not acting as an exact antenna.
