Why do radios sound tuned when your hand is on the tuner
January 12, 2023 1:27 AM Subscribe
But turn to static as soon as you walk away? Or even let go of the tuning dial? Please help me understand the reasons for this long-running source of low-level frustration in my life.
Best answer: The static sound happens when the radio has a weak signal and the Automatic Gain Control increases the signal amplitude until background noise becomes audible.
The presence of your body near the radio antenna is supplementing the radio signal through capacitive coupling.
Moving the antenna to where your body is, or fitting a larger antenna will improve the signal, and with a strong enough signal this effect will disappear.
posted by Lanark at 2:52 AM on January 12, 2023 [19 favorites]
The presence of your body near the radio antenna is supplementing the radio signal through capacitive coupling.
Moving the antenna to where your body is, or fitting a larger antenna will improve the signal, and with a strong enough signal this effect will disappear.
posted by Lanark at 2:52 AM on January 12, 2023 [19 favorites]
Best answer: You're a great (ok, mediocre but functional) aerial due to your metal content!
More due to the fact that you're mostly salty water.
posted by Johnny Assay at 4:14 AM on January 12, 2023 [28 favorites]
More due to the fact that you're mostly salty water.
posted by Johnny Assay at 4:14 AM on January 12, 2023 [28 favorites]
Best answer: Moving the radio to different places within the room can help as well.
FM radio broadcasts in a frequency range of 88-108MHz, which corresponds to wavelengths of 3 metres give or take, and in marginal signal areas where much of the signal is arriving via reflections, those radio waves will often light up the space in a complicated 3D pattern of standing waves whose detail size is of roughly half that wavelength. So it might well be that all you need to do to get a better signal is move the radio out of the node it's currently in to a nearby antinode, which could be less than a metre away.
Because each channel operates at a different frequency and therefore a different wavelength within that range, different channels will make different standing wave patterns. Likely as not, the brightest spot you find for any given channel will not also be the brightest spot for another.
This is also the reason why when you're out in the car and the radio fades badly as you pull up to a traffic light, sometimes all you need to do to restore good sound is roll a couple of feet forward or backward.
posted by flabdablet at 5:21 AM on January 12, 2023 [6 favorites]
FM radio broadcasts in a frequency range of 88-108MHz, which corresponds to wavelengths of 3 metres give or take, and in marginal signal areas where much of the signal is arriving via reflections, those radio waves will often light up the space in a complicated 3D pattern of standing waves whose detail size is of roughly half that wavelength. So it might well be that all you need to do to get a better signal is move the radio out of the node it's currently in to a nearby antinode, which could be less than a metre away.
Because each channel operates at a different frequency and therefore a different wavelength within that range, different channels will make different standing wave patterns. Likely as not, the brightest spot you find for any given channel will not also be the brightest spot for another.
This is also the reason why when you're out in the car and the radio fades badly as you pull up to a traffic light, sometimes all you need to do to restore good sound is roll a couple of feet forward or backward.
posted by flabdablet at 5:21 AM on January 12, 2023 [6 favorites]
Response by poster: It's true I am both pretty metal and kinda salty
posted by happyfrog at 5:23 AM on January 12, 2023 [64 favorites]
posted by happyfrog at 5:23 AM on January 12, 2023 [64 favorites]
Best answer: Because your body is conductive and is also somewhere near a half wavelength for FM, it will modify the standing wave pattern in your own vicinity. So don't be surprised if you find you can move the radio to a spot that sounds really good, only to have it fade horribly again as you move yourself back to chopping veg at the kitchen table.
When that happens, sometimes you can get good results by moving the radio to a spot that actually sounds terrible when you're in the process of moving it there, but comes good as you shift your body away from the radio and back to your normal listening spot.
Be warned, though, that the longer you spend on trying to get this just right, the higher the chance that a long-lost cousin will turn up in a huge RV and park it in your driveway and mess the pattern up altogether.
posted by flabdablet at 5:27 AM on January 12, 2023 [7 favorites]
When that happens, sometimes you can get good results by moving the radio to a spot that actually sounds terrible when you're in the process of moving it there, but comes good as you shift your body away from the radio and back to your normal listening spot.
Be warned, though, that the longer you spend on trying to get this just right, the higher the chance that a long-lost cousin will turn up in a huge RV and park it in your driveway and mess the pattern up altogether.
posted by flabdablet at 5:27 AM on January 12, 2023 [7 favorites]
Best answer: Or even let go of the tuning dial?
The other effect that may be in play here is hand capacitance. The tuning control in an analogue radio is a variable capacitor adjusting the frequency of a local oscillator to match (or be a fixed offset from) the frequency of the station you're listening to. But your hand also has some capacitance - so moving your hand around near the tuning control shifts the frequency as well and knocks the radio out of tune. Radio designers put a lot of effort into minimising this effect, but a cheap or simple radio is likely to suffer from it to some extent.
If you go the other way and build a radio that maximises the effect of hand capacitance, you get the theremin.
posted by offog at 5:35 AM on January 12, 2023 [8 favorites]
The other effect that may be in play here is hand capacitance. The tuning control in an analogue radio is a variable capacitor adjusting the frequency of a local oscillator to match (or be a fixed offset from) the frequency of the station you're listening to. But your hand also has some capacitance - so moving your hand around near the tuning control shifts the frequency as well and knocks the radio out of tune. Radio designers put a lot of effort into minimising this effect, but a cheap or simple radio is likely to suffer from it to some extent.
If you go the other way and build a radio that maximises the effect of hand capacitance, you get the theremin.
posted by offog at 5:35 AM on January 12, 2023 [8 favorites]
Best answer: Or to put it another way, as a friend who is an RF engineer said to me: "For all your wonderful personal qualities, to me you're just a two meter cylinder of salt water."
posted by range at 6:56 AM on January 12, 2023 [11 favorites]
posted by range at 6:56 AM on January 12, 2023 [11 favorites]
Best answer: You're a great (ok, mediocre but functional) aerial due to your metal content!
More due to the fact that you're mostly salty water.
I've read that you can increase the range of a car's door unlock fob/remote starter by placing it near your head when using it for this very reason. I try it every once and a while but I'm never sure if doing this actual does anything.
posted by any portmanteau in a storm at 11:49 AM on January 12, 2023 [2 favorites]
More due to the fact that you're mostly salty water.
I've read that you can increase the range of a car's door unlock fob/remote starter by placing it near your head when using it for this very reason. I try it every once and a while but I'm never sure if doing this actual does anything.
posted by any portmanteau in a storm at 11:49 AM on January 12, 2023 [2 favorites]
I've personally tested a version of that fob range increase manoeuvre that involves poking myself under the chin with the tip of the key before pressing the buttons, and can confirm that given a clear line of sight it approximately doubles the distance at which the car will respond.
The most likely mechanism behind this increase is that the human body is acting as a vertical whip antenna, redirecting into a mostly horizontal plane some radiation that the tiny antenna in the fob would otherwise be sending uselessly skywards.
posted by flabdablet at 11:13 PM on January 12, 2023 [2 favorites]
The most likely mechanism behind this increase is that the human body is acting as a vertical whip antenna, redirecting into a mostly horizontal plane some radiation that the tiny antenna in the fob would otherwise be sending uselessly skywards.
posted by flabdablet at 11:13 PM on January 12, 2023 [2 favorites]
Response by poster: OK so as a result of these answers I moved the amp about two inches to the left, I have crystal clear reception of my local community radio station, no matter where I'm standing, and I conceive of myself as, among other things, a two meter cylinder of salt water. My life is improved! Thanks MeFites.
posted by happyfrog at 3:29 PM on January 13, 2023 [3 favorites]
posted by happyfrog at 3:29 PM on January 13, 2023 [3 favorites]
This thread is closed to new comments.
posted by london explorer girl at 2:48 AM on January 12, 2023 [17 favorites]