Media alt text:
3D render of old tv set with animated static on its screen, as if tuned to a dead channel.
If you put a TV in a Faraday cage that blocked the relevant radio spectrum, would there be no static on it? I expected the answer to be a quick Google, but it wasn’t.
That is a good question, but I suspect if you tried this in real life it would still show static.
- The waves are amplified with a circuit that attempts to find a signal even if it’s very weak (so you can get a picture even if you’re close or very far from the tv station)
- At a certain point, the electromagnetic field from the running TV itself would start to get picked up
I suspect a better thought experiment would be if you just disconnected the input and amplification circuit entirely from the CRT tube, in which case you would probably just get white as the electron beam scans back and forth without any modulation.
Let me turn that around:
Would a TV still show static if you disconnected the input and amplification circuit outside a Faraday cage?
You’d still see static from the TV itself and any radiation that passed in to the cage. It’s not a perfect EM blocking device like TV shows and movies would have you believe.
Even if the Faraday cage blocked all RF perfectly, the Johnson noise would still produce plenty of static.
This is a very non scientific answer, but when I was a kid (good 40 years ago) I remember having a science book that called TV static “an echo of the big bang”. I guess that would mean just randomly scattered energy bouncing around on all bands?..
I could probably Google it and give you an answer, but I’ll just wait for someone with a more convincingly and authoritatively written reply.
Not all of it. But parts of it really are due to the cosmic microwave background radiation. Light from the moment the universe was transparent enough to let light spread. It’s from about 300,000 years after the big bang if I recall correctly. It’s the earliest image of the universe we have. And it’s more or less everywhere.
but I’ll just wait for someone with a more convincingly and authoritatively written reply.
Pfft sprayed my drink lol
Well apparently now astrophysicists are saying maybe the Big Bang didn’t happen. ¯_(ツ)_/¯
Since the last Lemmy update, if i delete a comment, it stays there sayin’ “deleted by creator”, just like yours.
Anyway, i wanted to see if I could still reply to a deleted message and I could, as i am writing this reply rn.
Very confusing for me is that, at least on my client on Android, your deleted message is displayed full and clear above the reply box.
Is this the intended behavior of deleted messages on Lemmy, it just hides the message, but it’s still available for anyone to read if they hit reply?
Uh Oh
IIRC, literally the background radiation of the universe.
The TV will try and amplify and display any signal. Without a station, it will end up amplifying random radio noise and tiny fluctuations in the amplifier circuits themselves.
The momentary signal strength is interpreted as brightness of a spot which is rapidly scanned over the display. In this case the signal is random so every spot on the screen will be a random brightness, changing every frame.
Modern digital TVs won’t do this, because with compressed video recognizable data is needed to even attempt displaying a picture.
As for the sources of the radio noise, most of it is from electrons being jostled by heat, some from space. (Including the cosmic microwave background others have mentioned)
The electron jostling (thermal noise) is the reason the receivers on radio telescope as cooled to insanely low temperatures often with liquid helium.
This is the closest to the correct explanation. The reason televisions based on AM radio reception showed static is because of a circuit called the AGC (Automatic Gain Control) which worked like a robotic volume control. Its job is to keep the recovered video signal within a certain amplification range. As long as there was a carrier (the TV station was “on the air”), you’d see whatever the station broadcast. But when they turned off their transmitter, the signal strength would fall and the AGC would increase the amplification until what you see is white noise, mostly due to the random motion of electrons in the electronic components. We can minimize that by cooling, but it can’t be totally eliminated. Audio amplifiers often come with a “hiss” specification that tells you how much of this kind of noise you can expect at normal operating temperature.
BTW, modern digital TVs -will- show a noise picture if they lack a video muting function when no carrier is detected. I have an LG bought in 2019 that does this, and it’s hella annoying when I accidentally hit the input selection button on the remote, switching from HDMI to TV reception.
Waves are everywhere. The TV picks up whatever waves it can. Some of those waves are signals meant to transmit an image (eg from a broadcast tower), others are just random noise in our environment.
Not an expert, but that was my understanding
“Waves are everywhere” made me think of the Feynman’s “Seeing Things” video. “Tremendous mess of waves”
It’s been awhile since I’ve messed about with this, so I don’t remember (and you may not either, so this is an open question), but wouldn’t it produce the effect even if disconnected from an antenna?
If so…Would the same principle be in play of it picking up on general EM waves to cause the effect?
Yeah, the same way a radio tuned to a station could be static until you plug in an antenna.
You could also get hums and interference from other sufficiently strong EMF sources, like how AM radios can pick up the sound of transmission lines
Afaik the antenna is picking up the background waves/radiation and the TV is displaying that background waves/radiation. If you disconnect the antenna, the TV will have no signal to display, it’ll be as blank as it can get.
