Why did old TVs produce an awfully loud static noise and weird visual when they had no signal rather than showing nothing like newer TVs do?
In: Technology
Old TVs used analog signals. The signal they received was directly converted to audio and video. If the TV was receiving no signal, it would still pick up background noise from radio waves, atmospheric noise, or electric grid noise. The TV can’t tell the difference between that and a real signal, so it does its best to “show” you the noise.
Modern TVs receive a digital signal, effectively a constant stream of data “packets”, tiny video files in a particular format. Noise doesn’t look like a data packet, so the TV knows to ignore it.
Because they did not know they had no signal. They just displayed raw data from the antenna.
If someone was transmitting, that was a TV video. If nobody was transmitting or the signal didn’t reach the TV because your antenna was broken or not plugged in, it just received and displayed the static randomness that’s in the air.
Those old TVs used discrete analog components. There is no central processing unit to coordinate things. They simply react to the electrical signals that arrived on the antenna. So when there is no usable signal, the components don’t know that and still try to decode whatever tiny random signals show up on the antenna. The static sounds and “snow” visual is just what happens when those components try to decode random radio signals.
Think of something like a water pump. It’s designed to pump water and does it well but it doesn’t know when there isn’t water in the pump and will just try to pump air instead and make a terrible weird noise.
To add to what others have said already. Static is actually a signal it’s the cosmic background radiation from the big bang.
That static is the *cosmic microwave background*, which is a constant low-level bath of light in the radio/microwave range that’s probably the light from the very early universe* cooling down, and the smoking gun evidence for the Big Bang theory. It’s the same signal being picked up as radio static.
*Like, earlier than any stars, just a hot cloud of hydrogen atoms.
They always had a signal. That static was electromagnetic radiation from very shortly after the big bang, travelling through space for around 14 billion years before finally hitting the TV’s antenna. The TV was showing noise from near the beginning of time.
CRT televisions fire an electron beam at a mesh of phosphors that glow when they get shot by the beam. when the CRT is turned on, that beam is aimed by the TV signal. when there is no signal, the beam is still on, and ambient radiation is enough of a signals to cause the electron beam to flail about wildly, striking randomly and creating the “snow”
an LED screen has a small computer that can understand when it’s not getting real data. but even if they didn’t, and you were able to run the hardware, it would just be solid white. getting anything other than the solid white backlight requires multiple signals working in tandem, and background radiation can’t do that sort of coordination. that’s why the LED needs the built-in computer to begin with.
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