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CATV question

Old 11-10-2008, 08:46 AM
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Default CATV question

Can anyone tell me what the source selector switch or mode (Norm/CATV) switch does on a TV? My little girl was playing with the remote and changed it to norm and it took a while to figure out what she did but then I could not figure out what exactly the switch does. Are cable and OTA modulated differently, different frequencies, etc?
Old 11-10-2008, 12:42 PM
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Default Re: CATV question

I believe the swith is used to go from TV/Antenna to Cable?
Old 11-10-2008, 01:55 PM
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Default Re: CATV question

I was wondering what it actually does to make it go from an over the air transmission to cable.
Old 11-10-2008, 02:38 PM
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Default Re: CATV question

In tv mode the tuner recognizes all channels above 13 as being in the uhf band, in catv mode it is in the vhf mode I believe
Old 11-10-2008, 05:58 PM
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Default Re: CATV question

Normal mode - use this mode for rabbit ears or outside antenna (non digital). It will put the tuner in a mode to receive VHF low band (ch. 2 - 6), VHF high band (ch. 7 -13), and UHF band (ch. 14 - 83)

CATV mode means cable TV and puts the tuner in a mode to receive cable bands. There are several bands within the cable mode and depending on the age of the set can go up to channel 100 something. The very first cable tv's only went up to ch. 36.

If you are using a cable box or satellite box it wont matter which mode you are in as the TV will stay on ch. 3 all the time or a video input (which does not use the tuner at all).
Old 11-11-2008, 08:28 AM
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Default Re: CATV question

baypro21 - 11/10/2008 3:58 PM

Normal mode - use this mode for rabbit ears or outside antenna (non digital). It will put the tuner in a mode to receive VHF low band (ch. 2 - 6), VHF high band (ch. 7 -13), and UHF band (ch. 14 - 83)

CATV mode means cable TV and puts the tuner in a mode to receive cable bands. There are several bands within the cable mode and depending on the age of the set can go up to channel 100 something. The very first cable tv's only went up to ch. 36.
Sorry guys, I am not explaining my question very well.

Whether the antenna is attached for OTA broadcast or cable is attached, it is connected using the same 75 ohm coax plug. Both OTA and cable are RF signals that go to a tuner in the tv to be converted to the audio and video that we see and hear. My understanding is that both OTA and Cable RF signals are the same frequency for each channel so when selecting normal or catv what does that do? Are the RF signals modulated differently, or they not really the same frequency, etc?

Thanks
Old 11-12-2008, 06:37 AM
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Default Re: CATV question

They are only the same frequency on channels 2-13. In the analog world they are modulated the same NTSC.
Old 11-12-2008, 10:10 PM
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Default Re: CATV question

crabpot is correct, the tuner will act the same in either mode if you are on channels 2 - 13. Above channel 13, say channel 25 for instance, in normal mode the tuner would be looking for a UHF signal of a certain frequency, in the CATV mode the tuner would be looking for a completely differant "cable freqency". Most, if not all the cable channels (14 and up) are actually located below channel 2. Also a channel is a 6 MHz wide range which contains video, color, and audio in differant areas of the signal. Channel 2 for instance has a lower limit of 54 MHz and a upper limit of 60 MHz. The video is located 1.25 MHz above the lower limit, color is 3.58 above and aural (audio) is 4.5 MHz above.

In short, to answer your question, the frequencies are differant.

The tuner has this ability to receive differant signals and convert them all to the same thing so the circuit directly downstream of the tuner always gets the same frequency. These downstream circuits separate the video, color, and audio signals.

"I can fix it, my dad is a TV repairman, he has an awesome set of tools".

Old 11-13-2008, 08:32 AM
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Default Re: CATV question

baypro21 - 11/12/2008 8:10 PM

"I can fix it, my dad is a TV repairman, he has an awesome set of tools".

Close, but in my house it is: Baby, I can fix it, I am an engineer, how hard can it be?

Actually, my wife is tired of me running cables everywhere for different things so I am trying to devise a wireless audio/video system for my house and garage.

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