A concept I never understood and would like an answer to

Discussion in 'DirecTV TiVo Powered PVRs & Receivers' started by kiddk1, Jan 7, 2009.

  1. Jan 7, 2009 #1 of 12

    kiddk1 The KIDD

    Oct 9, 2003


    I understand that if you want to get HD you need either a component or HDMI cable coax will not work, all the companies I have been with all use coax to run the wire from the pole or dish to your house, how is it that we can get HD while they use coax or does the cable/sat box upconvert? thanks
  2. Jan 7, 2009 #2 of 12

    wedgecon Just Plain Awesome TCF Club

    Dec 28, 2002
    Vancouver, WA
    Well your TV will get HD from an antenna connected via coax. In theory you could use coax for everything but consumer electronics devices typically have used lighter and easier to manage cable for their devices. Just be aware that not all TV's will accept HD from component. In the case of my TV I can get 720P but not 1080P from component. I have to use HDMI for 1080P. Of course this has nothing to do with technology, just politics.
  3. Jan 7, 2009 #3 of 12
    Joe Smith

    Joe Smith Medium Member

    Aug 1, 2003
    The connection from the cable company is regular coax from the pole to your tuner. The tuner can be a box leased from the cable company, or it can be a built-in device using CableCARD technology, such as TiVo.

    When it comes to bringing the signal from the tuner/recorder to the TV, that's where coax is not good enough. Neither are composite cables (yellow RCA jacks) nor S-Video cables (black 4-pin connectors). They can only do 480i; definitely not high definition.

    The cables running to HDTV source to your TV are the ones that need to be component or HDMI.
  4. Jan 8, 2009 #4 of 12
    Matt L

    Matt L Member

    Aug 13, 2000
    Flushing, MI
    It really has nothing to do with the wire per say. I make my own component cables out of coax, so yes coax will handle an HD signal. It's the processing that requires different connections. Basically ANY audio cable can be used for a component hook up, well maybe not the super cheap ones... But, back on point there is nothing "special" about component connections, it's just a shielded wire carrying part of the HD signal, in this case 3 are needed.

    HDMI is simply a construct so that most people wont be tempted to use a pure digital signal in a way the originators do not want.
  5. Jan 8, 2009 #5 of 12

    mr.unnatural Well-Known Member

    Feb 2, 2006


    The coax run to your house carries different signals than the ones that run between your STBs, DVRs, and TV. The coax feed to your house requires a much wider bandwidth to handle all of the signals being transmitted. Your STB tunes and decodes the signal you select (i.e., channel) and outputs a single signal (a combination of both audio and video for a single channel) that is handled at a much lower frequency. The HDMI and component cables are designed to handle these signals. As indicated, coax will also work fine for analog component signals, but HDMI uses many more connections to carry the various digital audio and video signals between components.
  6. Jan 9, 2009 #6 of 12

    TyroneShoes HD evangelist

    Sep 6, 2004
    True, but let me give it a try:

    For a device to carry a signal over common RG-6 or RG-59 cable to a TV, the sending device has to have a modulator built into it, and the receiving device has to have a demodulator (tuner) built into it. An NTSC modulator is functionally equivalent to an analog TV transmitter, but on a much smaller scale, power-wise. Any TV expecting an OTA analog signal will be just as happy with the same sort of signal coming to it from the local modulator of a VCR or DVR.

    In the 70's, it became common for VCRs to have a NTSC modulator built into them so that they could connect to TVs of the day, which generally did not have baseband inputs (but of course had NTSC tuners by definition). It added less than $5 to the manufacturing cost and allowed compatibility to virtually any TV. Instead of exiting the VCR as baseband, the signal was remodulated to CH 3 or 4, where it was then demodulated back to baseband in the TV.

    As VCRs were replaced by DVRs, they too typically had modulators, for the same purpose.

    By the turn of the millenium, video games and DVD players were common and so baseband inputs on TVs became ubiquitous, and were on nearly every set out there, making the built-in modulator mostly unecessary. By the time folks were buying HD sets, they all had baseband inputs, even for NTSC.

    So, HD DVR manufacturers really could do away with NTSC modulators, and some have.

    But to make the HD signal work over RF cable, you would not be able to use an NTSC modulator, but would need an ATSC modulator (which uses the same 8VSB modulation format as OTA digital television stations use), which is really not a common consumer product at all, even if it exists at all, which is doubtful. And even if it did, it would add $40-50 to the manufacturing cost, at least.

    Since there are at least 2 other ways to move HD to your display, the ATSC modulator as a built-in is a bad business choice, and a non-starter.

    Not only that, but the content providers would be up in arms. If you had an ATSC modulator on your HR2x, that would mean you could chain two HR2x's together and make pristine digital copies via RF in the same manner that you can make less-than-pristine copies of SD DVDs by chaining a DVD Player and DVDR together (or two VCRs), baseband analog output to baseband analog input.

    You may have noticed that there is shockingly no digital path in to any DVD recorder, even though it is, ironically enough, strictly a digital-only recording device, and this is exactly why. Content providers squawk very loudly when the means to copy content within the digital domain is placed in the hands of the consumer, which is exactly why we don't have that technology available to us.
  7. Jan 9, 2009 #7 of 12

    jlib Lean Forward

    Nov 21, 2002
    Nice explanation! It is mainly just historical/legal reasons, then, rather than technical reasons that the single coax output on consumer AV equipment remains SD composite.
  8. stevel

    stevel Dumb Blond TCF Club

    Aug 23, 2000
    Nashua, NH
    The coax output is NOT "composite". It is RF modulated as if it were an analog OTA broadcast on channel 3 or 4, along with mono audio. (Stereo modulators do exist, but I've never seen one built in to a VCR/DVR.)

    In order for a device such as a DVR to send a HD signal over coax, it would have to have an ATSC modulator. Theoretically possible, but likely more expensive than the whole box to begin with. Since all HD sets have at least component if not HDMI inputs, and HDMI satisfies the protection desires of the "content providers", there's no motivation for CE manufacturers to include an ATSC modulator.
  9. jlib

    jlib Lean Forward

    Nov 21, 2002
    Duh! :eek: Thanks... For it to be composite it would just be a single RCA cable. I must have been thinking of that...
  10. jlib

    jlib Lean Forward

    Nov 21, 2002
    Then once you grasp the limitations forced upon consumer equipment for the reasons so eloquently explained by the posts above, look up HD-SDI which is what TV studios and professional equipment uses. So, on a technical level, a coax will work it is just that you aren't as likely to run into it in your living room.
  11. TyroneShoes

    TyroneShoes HD evangelist

    Sep 6, 2004
    Well actually, the signal over RF cable is usually baseband composite NTSC video (and baseband audio) modulated onto an RF carrier. So it really is both. The protocol for the information itself is NTSC composite, which is the very same signal that is seen on the "yellow" connector of the baseband connections (and baseband mono audio which is what is on the red and white connectors although that is usually mono-ed together for a single audio carrier), while the protocol for the modulation is AM (for video) and FM (for audio). The term "NTSC composite" stems from the original NTSC matrixing process in cameras, where the video components R, G, and B are matrixed together into a "composite" video.

    HDSDI is a beefed-up version of normal serial digital interface or SDI, and yes it does travel over coax in pro installations, but the scope of the question was narrowed to consumer usage, where virtually all RF distribution is still NTSC analog composite. The TV industry adapted SDI readily when converting from analog to digital because the cabling is very similar and so is the manner it is worked with and designed/installed.

    HDSDI is uncompressed digital video (possibly with embedded AES audio) and is what your TV station uses if they uncompress MPEG-2 network feeds that arrive (typically in ASI format) so that they can manipulate the video locally before final SMPTE310 compression, which reverses the process (takes the HDSDI and compresses it to a higher level of MPEG-2 compression than it arrived as). This allows them to do things such as time (synchronize) the signals, add graphics, run local crawls, etc. FOX stations avoid this decompress/recompress step by keeping things in the MPEG-2 compressed domain and bit stream splicing to switch in local content and graphics.

    HDSDI is very similar to HDMI, in that the bit rate is similar, it has a similar structure for packetized delivery, it is uncompressed, and it can carry embedded digital audio. It does not have the conditional access issues that HDMI has, however. HDMI is as rare in the professional world as HDSDI is in the consumer world, but they are first cousins, technically speaking.
  12. lofar

    lofar New Member

    Mar 21, 2008
    How about this..

    Because as more and more electronic devices began to hook up to a TV we needed more and more ports. It became expensive and inefficent to keep putting modulators and de-modulaters onto the end of devices to continue with coax. Anyone remember the early days of nintendo, super nintendo, sega, VCR's and DVD players? I used to have a DVD player chained into a VCR chained into an RF modulator for the nintendo, chained into the RF modulator for the super nintendo, chained into the modulator for the sega all connected up to the TV. And I was the only one in the house that could figure out how to get it all to work. :)

    Now we just spam the input button on the remote until the TV tells us what device we want to view.

Share This Page

spam firewall