When one changes the channel on a radio or a t.v. to a channel with no signal why is there static sound what causes that? If there aren’t any signals, wouldnt it stand to reason there should be silence?
I have a minimal understanding of radio waves and all that fun stuff, fight my ignorance!
But there is a signal - a low random one created by many things. Some of it is caused by thermal effects in the circuitry of the radio receiver, some of it comes from nearby electrical devices like computers and lighting. Some of it is caused by lightning. Some of it comes from other radio transmitters some distance away, or on a resonant frequency. Some of it is cosmic noise.
It is impossible to avoid completely, though it is possible to shield circuits from some of this noise, minimize sources of others, and amplify the signal that is desired.
Ahh so static is basically a jumble of weak signals? I love that some of it is cosmic noise. I will be tuned in on the drive home today, thinking to myself " yay im a radio astronomer"
Radio waves are part of the electromagnetic spectrum that is all around us all the time, both from man-made objects (radio transmitters, WiFi, satellites, microwaves, machinery, appliances, etc.) and natural objects (the Sun and stars, rocks, etc.)
The frequencies that we tune in are modulated, that is they contain information that can be extracted and decoded. The method of modulation can be by frequency (FM), by amplitude (AM) or various digital schemes.
When you tune your TV or radio to a part of the spectrum with no available modulated signal, the receiver is “looking” for a carrier signal in the frequency channel that you’ve chosen.
Because no modulated carrier signal is found, the receiver is basically listening to all of the available background electromagnetic radiation that passes through the filter stages. If you had tuned to a frequency with an available carrier signal then the signal strength is so large that it drowns out the background radiation.
I read that cooling the circuits can cut down the white noise. How the heck does cooling them reduce static? I may be mistaken but I think they do this on radio telescopes.
Thanks for the replies guys, consider my ignorance beaten into submission…for now!
Because the signal amplifiers themselves are sources of noise. Cooling them reduces this “thermal” noise.
where the desired electronic signal is weak or infrequent then cooling of the detector or electronics would be done, done in radio and other types of electronics.
Back in the days of analog TV, one could set one’s receiver to VHF Channel 2 (54-60 Mhz) turn the set’s brightness all the way down to near-black. Lightning would generate bright streaks on the TV, while a nearby tornado caused an overall glow.
That’s not quite as far-fetched as you might think! The cosmic microwave background was discovered because Penzias and Wilson were investigating the sources of interference on a very sensitive antenna. Discovery of cosmic microwave background radiation - Wikipedia
Actually, Digital TVs shouldn’t have static. Old TVs were analog TVs. They tried their best to interpret the random fluctuations and display the results on your screen. Digital signals are different. You either have something, or you don’t. One of the reasons we switched to digital was to eliminate snow, ghost images, and static. Of course, one of the problems is that if you can’t get a strong picture, you don’t get anything.
Radio is still analog (although that may soon change too). That means you can still pick up static between stations and some of that static does come from cosmic rays.
tv is still analog in much of the world. analog tv sets are still plentiful and in good use in the USA, they are sourced by a digital tuner, cable, satellite.