can't get rid of video noise - AVS Forum
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Old 07-08-2001, 01:55 PM - Thread Starter
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does anyone know of a good primer on the web about video distribution? i built the house with good quality RG-6 yet i am getting a grainy/snowing picture with basic cable distribution. if i connect where the cable comes into the house it looks ok but at the other end of the wire in a room it looks bad. no ghosting and no non-random noise. just grainy and snowy looking. happens with only one room connected and no splitters in the path. i tried a booster and it does not help. does not seem to be worse with high channels so i suspect it is not tilt and i am seeing it on even short runs.

greg

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Old 07-08-2001, 03:35 PM
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A CATV run of 100ft or less you should be OK with one TV and no splitters in the line. If you tried a CATV amp with level adjustments, and did't help try replacing the coax connectors. Its possible you might also have a staple/screw in the coax line.

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[This message has been edited by David Richardson (edited 07-08-2001).]
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Old 07-09-2001, 04:39 PM
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We have a primer on video distribution on our web site: http://www.channelplus.com/AP_note_files/howdoi.htm . However, this probably won't answer your question.


Do you have the same problems with VHF and UHF signals? Older TVs have separate inputs for the UHF tuner.

Check the center conductor of the cable as it enters. If very short, it may not be contacting the blades of the F-connector splice.

Be sure that you actually are working from the ends of the same wire. This sounds dumb, but a lot of professionally installed systems are labeled wrong. If you think you are connecting the den but instead are connecting the cable that runs to a bedroom, the den TV may exhibit the problems you state: very weak signal, amp does not help, higher frequencies don't get worse.




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Old 07-20-2001, 06:22 PM
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The modulator is "trumping" the CATV signal. The Modulated signal is to high. Turn the gain down and/or install a 10db ant. "Pad" from RS.

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Old 07-20-2001, 10:13 PM - Thread Starter
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ok i have isolated this and it is weird. bought all new splitters and made all new cables VERY CAREFULLY. i have cable coming in going into a two way channelvision 1ghz combiner. the other leg of the combiner is the modulator. and the output goes to an RF amp and through a 1 x 8 , 1Ghz splitter to the house. modulator set on channels 90, 93 and 96. the picture on all lower channels is full of snow. unplug the power to the modulator and the cable looks perfect! so i'm thinking i have a bad modulator that is spraying noise at all freqs. i replace it with a different brand and it does the same thing.

what the heck is going on here?

greg

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[This message has been edited by indygreg (edited 07-20-2001).]

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Old 07-22-2001, 09:12 AM - Thread Starter
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dave, you were right. seems there is no replacement for experience. a couple quick questions if you don't mind.

- i put 8 way splitters in for future expansion but now have trouble driving enough signal to the house. do the unused ports of a splitter load the amplifier? i have 75ohm terminators in them. is that the issue?

- is there some more scientific way than trial and error to know how many db of signal i have? do i need a scope?

greg

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Old 07-22-2001, 11:36 AM
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Rough CATV Guide.

Average CATV signal into a house is 5db.

Average loss for a 2 way splitter is 4db.
Average loss for a 4 way splitter is 7db.
Average loss for a 8 way splitter is 12db.

Each port is on average that amount of drop in db. So terminating the unused ports doesn't really give you more signal it prevents "RF leaks" and unwanted RF injection.

Your upper channels lose signal much faster over coax because of the higher freq. so I always have my modulated signal higher. Also installing a CATV freq. filter to filter off any noise from CATV provider where the modulated channels are will do wonders. Ones such as channel plus LPF-480,600 work like a charm.

Dave


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