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Discussion Starter · #1 ·
I had a technician come out today to see if he could increase the volume of the audio coming off of my Comcast digital cable boxes which he was able to do somewhat. While he was checking the signal we were discussing digital cable. I was asking about ATSC and whatnot and we some how got around to the signal that is actually coming into the house. He said "there is no such thing as a digital signal coming into a house" over cable except in the case of fiber optic to the premises. He explained that the signal comes in to their head end as a digital signal and then is converted to analog for transmission. It then is converted back to digital in the cable box. This guy was probably the most knowledgeable tech I've ever come out to my house, but I can't help thinking he was somehow confused or at least that I didn't quite understand him. It is obvious that the first 29 channels are converted to an NTSC signal for transmission. Otherwise a regular TV with an NTSC tuner could not pick them up. However, for channels above 29, it seems bizarre to me that they are broadcasting an analog signal which is then converted to digital by the box and then converted again to NTSC so the TV can display it. It is my understanding that digital signals are more bandwidth efficient. With this in mind, why would they convert to analog for broadcasting? Not to mention, it doesn't make sense that the box would convert an analog signal to digital, which would only degrade the quality, just to convert it to the analog NTSC signal that is necessarily the output, so it can display on a regular TV.(just in case anyone is wondering these cable boxes only have a coaxial out so it sends an NTSC and displays on channel 3, yeah, cheap) Can anyone explain this?
 

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He has no idea what he is talking about. Just one more misinformed person in a sea of misinformation about digital tv. The signals above whatever channel are indeed digital. Maybe he is one of many people that thinks QAM stands for "quadrature ANALOG modulation" instead of "quadrature AMPLITUDE modulation".
 

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Quote:
Originally Posted by blazerqb11 /forum/post/16984029


I had a technician come out today . . . my Comcast digital cable boxes . . . This guy was probably the most knowledgeable tech I've ever come out to my house, but I can't help thinking he was somehow confused . . . Not to mention, it doesn't make sense that the box would convert an analog signal to digital, which would only degrade the quality, just to convert it to the analog NTSC signal that is necessarily the output, so it can display on a regular TV.(just in case anyone is wondering these cable boxes only have a coaxial out so it sends an NTSC and displays on channel 3, yeah, cheap) Can anyone explain this?

I just responded to a post that raised these questions. My response is found here:

http://www.avsforum.com/avs-vb/showt...9#post16984179
 

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Discussion Starter · #4 ·
That is as I suspected. I think he got confused about what the box was actually doing. He somehow thought the box took a analog signal and made it digital, whereas it is actually taking a digital signal and making it analog.
 

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Quote:
Originally Posted by CRT Dude /forum/post/16986941


Would the RF signal traveling over coax be considered analog even if its carry digtal data?

No, it's still a digital signal. Being modulated onto an analog carrier doesn't change that. It's not being fundamentally changed from being a digital signal. Apparently the OP's tech doesn't understand the difference...
 

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OTOH... technically, it's all modulated as analog, be it QAM (cable) or 8VSB (OTA).


So, originates as a digital signal... translated onto an analog carrier... hits the STB (or QAM tuner in TV) and translates the carrier back to an ATSC (digital) signal for display.
 

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If u know about computer networks..... the PAYLOAD is digital, the transport (modulation) is analog.


If u don't understand this, and are concerned that *somehow* this is a conspiracy of the industry to make us pay more and buy new TVs...... DON'T WORRY ABOUT IT is all I can tell you. Don't loose any sleep over it.


I do notice my DTV channels, even the 480i look clearer than the analogs counterpart and that's good enuff 4me.
 

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Quote:
Originally Posted by Ratman /forum/post/16988919


OTOH... technically, it's all modulated as analog, be it QAM (cable) or 8VSB (OTA).


So, originates as a digital signal... translated onto an analog carrier... hits the STB (or QAM tuner in TV) and translates the carrier back to an ATSC (digital) signal for display.

Actually, ATSC has nothing to do with digital cable, but deep down you know that!
 

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I want some of what that tech is having.



The information that makes up the picture and sound is in digital format all the way from the content provider to QAM tuner. Doesn't matter if the QAM tuner is in the TV set or the STB. That digital information is superimposed onto an rf carrier, which is a sine wave (analog), but the information is in digital format, so they erroneously call it a digital signal. Same thing with DirecTV and Dish Network. The RF carriers that transport the information are sine waves (analog), but the information is in digital format, so they erroneously call it a digital signal.


It isn't that it is translated from digital to analog then back to digital. It is that the digital information is superimposed onto an analog carrier for transmission, then removed from that carrier for display.
 

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But yet again...

It is not a true (100%) digital signal end to end when using an RF modulation scheme (satellite -PSK, cable -QAM or OTA -8VSB).


The closest you can come to digital end-to-end is FiOS. The "weakest link" is from the ONT to the STB. I could be wrong...
 

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Quote:
Originally Posted by Ratman /forum/post/16993208


But yet again...

It is not a true (100%) digital signal end to end when using an RF modulation scheme (satellite -PSK, cable -QAM or OTA -8VSB).


The closest you can come to digital end-to-end is FiOS. The "weakest link" is from the ONT to the STB. I could be wrong...

Agreed
 

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So perhaps the tech is/was not wrong.


It may be how his information was interpreted and assumptions by others.
 

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Quote:
Originally Posted by egnlsn /forum/post/16992913


It isn't that it is translated from digital to analog then back to digital. It is that the digital information is superimposed onto an analog carrier for transmission, then removed from that carrier for display.

Sorry to belabor the discussion but...



Digital is a square wave (+ and - ) interpreted as a 1 or 0.

Analog is inherently a sine wave (peak and valley).


The square wave is essentially translated to a sine wave for transport and extrapolated at the other end from a sine wave back to a square wave.


Any RF "noise" from the headend to the STB can be introduced and misinterpreted as good "digital" info and produce artifacts or... errors in translation.



I side with the "cable guy".
 

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Now if you had written:

Digital is an "Analog" square wave (+ and - ) interpreted as a 1 or 0.

Analog is inherently a "series" of sine waves (peak and valley).

The (a) square wave is essentially an infinite series of sine waves.

Then I would agree with you!


The information is digital, but it is transmitted through an analog medium.

Or it could be transmitted through an FM medium, in other situations.
 
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