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#1
10-18-2011, 11:07 PM
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tv snow is caused in part by cosmic rays?
I had a fascinating conversation with an old tech today. We discussed tube audio gear, recording, and of course crt tv's and the death of NTSC.
He went on to tell me that the 'snow' we see on an unused channel contains background radiation from space, which lingers from the creation of the universe(!) I was nodding along politely, thinking this was total bullshit. Then when I got home I got on the net and ran a quick n dirty search, and to my surprise he was correct..Two sites I came across claim that this radiation is anywhere from a quarter to a third of the snow commonly seen on an analog tv screen. Bizarre to say the least. My question is as follows- how does a standard, nothing-fancy tv set pick this up? is it everywhere on earth? The guy I was talking to said you don't need any sort of antenna to see it. Confused 
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#2
10-19-2011, 12:58 AM
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Noise is generated in all components so that is a major source of noise when there is no signal to override it. Look up the subject of random electronic noise and you will find formulas to tell you how much you will see. It's temperature dependent so that's in the formula.
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#3
10-19-2011, 12:08 PM
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Thats what they told us in school but i dont believe it. They said every pulse of static was a distant star or planet exploding.
Well I got a question about that....why does the static not increase when you hook an antenna up on an unused channel?? You can cut the antenna leads right off the tuner and no change. With no signal the agc cranks the gain way up and noise from everything is amplified. I would blame the noisy carbon resistors before deep space. Maybe its a combination of everything.
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#4
10-19-2011, 11:20 PM
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that's what i'm asking too, ctc17. zero input to the tuner versus a big mast on an empty frequency, same snow. sometimes I get obvious 'man-made' interference when d-x'ing,, such as curving wave patterns/herringbone lines so it's hard to tell...
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#5
10-21-2011, 02:52 PM
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I believe the number is closer to a few percent. Of course that will depend on the antenna and how low noise your input section is. But even if it were 30% I doubt that you could tell the difference between the internally generated noise and adding 30% more noise. Especially if the AGC is kicking in.
The source is usually referred to as the cosmic microwave background rather than cosmic rays. Cosmic rays are high energy particles. John
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#6
10-21-2011, 07:46 PM
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My mistake re: rays vs. CMB. Would be interesting to remove agc so as to maintain a constant tuner input level and see the difference. This whole topic is pretty out-there but I was wondering if anyone had some light to shed on it .
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#7
10-21-2011, 08:45 PM
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Temperature of the big bang radiation is a few Kelvins, noise temperature of the tuner is hundreds of Kelvins. At lower VHF band, though, there is "galactic noise" which is taken into account when figuring the power needed for broadcasting. Unfortunately, this is where man-made noise is worse also, and it drowns out the galactic noise.
see this: http://en.wikipedia.org/wiki/Antenna_noise_temperature for some explanation
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