WARNING: six feet of sub-standard coax kills TiVo HD

Discussion in 'TiVo Series3 HDTV DVRs' started by Phantom Gremlin, Aug 1, 2007.

  1. Aug 1, 2007 #1 of 27
    Phantom Gremlin

    Phantom Gremlin Active Member

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    Tualatin,...

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    Many people are complaining about pixellation. I urge you to run the signal strength test first and also check cables and splitters carefully. Here's my story:

    I bought an TiVo HD last week. I hooked it up to my cable and found that I could only receive about half of the OTA HD locals channels that Comcast carries in QAM. The others were very marginal signal strength or even zero strength.

    I was using a high quality splitter so I knew that wasn't the problem. But for my initial hookup I grabbed 6 ft of "random" RG-59 cable I had lying around (because the cable had easy to use connectors on it).

    This coax turned out to be the problem. The QAM channels Comcast uses for carrying my HD locals are up at 600 MHz plus. My random 6 ft coax attenuated those signals *much more* than the 3.5 dB splitter and even much more than a 6 dB inline attenuator I added as an experiment once I realized what was happening.

    According to my cable modem status page (the other half of the split signal) I'm receiving about -9 dBmV of signal out of the splitter. That's just a little better than the lower end of the -10 dBmV recommended for my cable modem at broadband reports. And the TiVo HD works reliably with that signal level.

    Unfortunately just 6 ft of poor coax is all it takes to drastically attenuate signals at 600 MHz. And because it sort of "works", nobody thinks about the coax. Well, you should!

    What does the wiring in your house look like? If it has "grown like topsy" over the years, it may be the problem.
     
  2. Aug 1, 2007 #2 of 27
    aenima99x

    aenima99x New Member

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    That's probably part of the problem, you should be using RG-6.
     
  3. Aug 1, 2007 #3 of 27
    LoREvanescence

    LoREvanescence Always Autocorrected

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    Salem, MA
    that is very true. Post people wont look at the coax cable it self. As long as the connection heads look clean and undamaged and are ones that you can screw in place to a tight connection I generally wouldn't think of the coax it self as the problem.

    Right now I have a fairly new standard 25ft coax cable in use off of my indoor antenna. I can only pick up one digital station, one that is broadcaster within 5 miles of my university. PBS is broadcasted less then 15 miles form here, and I get 0 signal strength? The antenna says I should be able to get stuff in good quality (digital) up to 30 miles, and decent upto 50 miles?

    Could I possible be losing signal strength in the cable, or could my indoor antenna just not be good at picking up signals form indoors sitting on the window sill.
     
  4. Aug 1, 2007 #4 of 27
    Illrigger

    Illrigger New Member

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    Heh, I've yet to hear of an indoor antenna than can bring in a channel from 50 miles. I was using a U-75R directional outdoor antenna (40" boom, 17 elements) and would lose signal on channels 30 miles away whenever the wind blew too hard and wobbled the mast.

    You might need to physically POINT the antenna in order to get good reception, and if there are trees and/or buildings in the way, good luck.

    That being said, your cables can indeed impact your signal strength considerably.
     
  5. Aug 1, 2007 #5 of 27
    LoREvanescence

    LoREvanescence Always Autocorrected

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    Salem, MA

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    What I have is a Trek HDTVi antenna pro (hdtv indoor antenna) which I got free with a $150 DVICO USB HDTV tuner for OTA/Clear Qam 64/256 2 years ago.

    IT says it supports VHF 40 Mhz - 230 Mhz (channels 2 - 13) and UHF 470 Mhz - 806 Mhzz channels 14 - 69.

    Tuning Quality

    0-15 Miles Excelent
    16-35 Good
    36-50 Poor
    50+ Not supported, an outdoor antenna required.

    Accourding to AntennaWeb New Hampshire Public Television is 15.6 miles away form my current address, and well in the range of a indoor antenna. Even AntennaWeb says I should get it with a indoor antenna.

    Now, as for placment, I can only point it in the direction facing outside the window.
    The signal seems to be unstable if it's not right at the window.

    I sent an email to NHPT about this, as I could pick up their broadcast from my home in Mass, 57 miles form the closest tower with this indoor antenna, granted I was at a high elevation. They told me that part of the city of manchester, mainly by the river could not get their broadcast because it is blocked by the terrain, the signal travels above this area. I really don't understand why, is the land for the most part, its relatively flat, no big hills or mountains near by. That also said this problem should be fixed when the FCC allows them to turn off their analog signal and broadcast their digital in VHF rather then UHF.

    Right now all I can pick up is WMUR (ABC) in HD, which is 7.2 miles away, and this Digital Spanish Network in SD from 23 miles away which I don't count and deleted out of my received channels list.
     
  6. Aug 1, 2007 #6 of 27
    LostCluster

    LostCluster Member

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    Digital will never be broadcast in VHF. Every station currently on VHF has a UHF allotment for their digital station. Where they are now is where they'll stay.
     
  7. Aug 1, 2007 #7 of 27
    wolflord11

    wolflord11 Lord of Darkness

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    Madisonville...
    Bingo!!! :D
     
  8. Aug 1, 2007 #8 of 27
    mikebridge

    mikebridge Member

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    Plainfield, IL
    i'm glad now i redid all the coax in my house w/ quad shielded RG6.
     
  9. Aug 1, 2007 #9 of 27
    MScottC

    MScottC Well-Known Member

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    NOT TRUE AT ALL. Whle UHF channels are preferable, and 7-13 in the VHF brand are preferred over 2-6, all channels are eligible for "election." Some stations indeed will be swapping their digital broadcasts over to their original VHF channels. Search the web, you'll see what I'm talking about.
     
  10. wolflord11

    wolflord11 Lord of Darkness

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    Madisonville...
    The RG59 is still the problem:

    "The frequencies that are used in High Definition are usually around 37 MHz. For those lower frequencies, an RG59 with an 95% copper all-copper shield is designed to block RFI inclusion at base band frequencies. RG59’s “big brother” is an RG6 Single Shield , which consists of the same makeup as RG59 but has a thicker center conductor, for less signal loss, and longer runs. Because RG59 does not have a foil shield, it shouldn't be utilized for satellite feeds or cable feeds."

    To read more:

    RG59 vs RG6

    :D
     
  11. JJ

    JJ TiVoPlantation Owner

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    Jul 14, 2000
    Land of...
    Please confirm
    so I can inform my local NBC station broadcasting HD digital on RF10 in the VHF spectrum...
     
  12. JANNINO

    JANNINO Member

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    Oct 27, 2004
    Is your RG-6 quad shielded? This could further improve signal strength.
     
  13. wolflord11

    wolflord11 Lord of Darkness

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    Madisonville...
    Actually this is incorrect:

    "RG6 Dual or Quad Shield shouldn't be utilized for base band applications, such as video projectors, component video, plasma TV’s, etc. It may sound like a great solution because of all the layers of shielding, but RG6 Dual and Quad Shield don't have the proper type of shielding for the above described applications. It is manufactured using foil shields and braided aluminum shields. The makeup of the shields differs between models. The effective range of operation for foil shields is above 50MHz, which makes them perfect for rejection of radio frequency interference, or RFI, that may have an effect on satellite or cable installations. At frequencies below 50 MHz, however, foil shields are not effective. The braiding on the RG6 Dual shield and the RG6 Quad shield doesn't have enough coverage to work effectively with baseband applications."

    See the link provided above.

    :D
     
  14. Dssturbo1

    Dssturbo1 New Member

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    Feb 22, 2005
    IF the OP meant the cable he used had those slip on type fittings= ("easy to use connectors"), instead of normal threaded connectors then that could also be a problem besides it being rg59.
     
  15. lrhorer

    lrhorer Active Member

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    San...
    Please don't read more. The article in this link is talking about baseband applications, not RF. There are also a couple f mis-statements, but they may just be typos. First of all, there are no television carriers of any sort at 37MHz - certainly not HD. The lowest allocated television broadcast frequency is 55.25MHz. This is VHF channel 2. At one time many decades ago there was a channel 1 at 49.25MHz, but the ubiquitous adoption of Superheterodyne receivers and the inherent problems of having Channel 1 at 49MHz and TVIF at 45MHz caused the industry (probably under FCC mandate, but of this I am not certain) to completely drop VHF Channel 2 circa 1948. 37MHz is just a bit above where most CATV companies place upstream signals going back to the headend, such as two way communications for their set-top cable boxes, digital phone service, and the DOCSIS transport via which the CATV company delivers broadband internet service.

    Now as it happens the analog bandwidth of HD transmissions is somewhere close to 37MHz, and could even be 37MHz as far as I know, but the effectiveness and suitability of a particular cable has virtually nothing to do with the signal bandwidth of any of the carriers of interest and a great deal to do with the center frequency of each of said carriers. Most Cable Companies place their digital streams between 400MHz and 750MHz, with some companies placing channels up in the 750MHz - 1000MHz region, as well. The decision to extend the signals into the 750 - 1000MHz range is a complex technical and economic issue with lots of variables, but the bottom line is almost every digital signal on the vast majority of cable subscriber's coaxial lines is above 350MHz and absolutely nowhere near 37MHz. They are also digital, not analog, so the analog bandwidth of the HD signal is irrelevant. (The analog bandwidth of an NTSC video signal is 3.8MHz, but the FM audio carrier is centered at 4.5MHz above the video carrier, so the total bandwidth for an NTSC channel is 6MHz, allowing for proper reception of the lower video sideband while simultaneously allowing for proper rejection of the lower adjacent channel's audio.)

    It is true RG-6 has lower loss and is thus generally more suitable for anything other than low frequency transmissions compared to RG-59, but it is not true that every RG-6 cable is better - even in high frequency applications - than every RG-59 cable. Both are available with different braids and foil configurations, including from 50% to over 95% braid, dual braid, no foil, dual foil, and dual foil / dual braid. They are also available with soft copper, OFHC copper, copper plated steel, and silver plated copper center conductors. Each has different applicability for different situations.

    All that said, a six foot long piece of even the cheapest 50% braid RG-59 is not going to loose significantly more than a six foot section of the very best RG-6. Specifically, neither will loose more than a fraction of a dB even at 1000MHz. 'Ordinarily, that is. A bad piece of either type of coax or one with a bad connector can loose a great deal of the signal. Not only that, but the cable's response may be horrible. The presence of a regularly spaced series of defects in the cable can result in a single carrier or small group of carriers being attenuated 20dB or even more. Poor shielding or cracked shielding is very likely to allow ingress carriers which will tear up blocks of channels (digital CATV carriers typically transport up to 6 HD channels and 16 SD channels each, and an ingress carrier will either take out the whole block, or nothing, perhaps intermittently). In one very, very weird and unusual case, I have even seen a bad cable (a 95% braid dual foil silver plated copper headend jumper) generate interference carriers of it's own. How it did this, I will never in my life be able to figure out - it shouldn't be possible - but both my boss and I absolutely confirmed the presence of spurious carriers on the jumper with a spectrum analyzer.

    The bottom line is, a bad jumper can cause all sorts of grief, and RG-6 is virtually always a better choice for UHF applications, particularly for long runs, but a good RG-59 jumper of short length should not ordinarily be a problem for HD transport.
     
  16. lrhorer

    lrhorer Active Member

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    Aug 31, 2003
    San...
    (Underlined capitals added by me.) We're talking about a TiVo, here, and we're talking about getting bad recordings on a Series III. The series III does not have any sort of baseband input whatsoever. The only baseband ports are the outputs, all of which are baseband of one form or another - composite, component, or HDMI, but those will not prevent the TiVo from recording a program without errors. The RF inputs carry signals between 55.25 and 1000MHz to the TiVo.

    The statement, however, is correct. Dual and quad shield cables are designed for broadband RF signals, not baseband. Foil shielding is definitely recommended for frequencies above 100MHz.
     
  17. doormat

    doormat Member

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    Sep 15, 2004
    Vegas
    Really?
    KVBC - 2
    KLAS - 7
    KLVX - 11
    KTNV - 12

    And I agree on the signal strength. I use the coax provided by the cable company, along splitters from them as well. Of course my house is only 2 years old so the wiring is fresh and works well.
     
  18. moyekj

    moyekj Well-Known Member

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    Jan 23, 2006
    Mission...
    I'm 70+ miles SSE from Mount Wilson broadcast towers in Los Angeles and I pull in all the network broadcasts at 80 or better signal strength on one of my S3s. The antenna I use: a cheap ($30) indoor amplified UHF antenna I picked up at Home Depot pointing NNW sitting on a shelf in the garage (with a thick wooden garage door in it's path) . Don't underestimate what these indoor antennas can do if pointed in the right direction.
     
  19. Phantom Gremlin

    Phantom Gremlin Active Member

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    Tualatin,...
    Okay, just for fun I made a flickr account and posted a picture of the connector there.

    http://www.flickr.com/photos/10835392@N05/983579518/

    The connector has a strain relief so is easy to grab, and also is attached a little better than a do-it-yourself crimp connection. I know not to use a slip on connector.
     
  20. Phantom Gremlin

    Phantom Gremlin Active Member

    1,579
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    Jun 20, 2002
    Tualatin,...
    Exactly. I've seen the attenuation curves for RG-6 and RG-59 and know that 6 ft shouldn't have made any difference. But in my case the difference was dramatic. That's why I wanted to warn people about being sloppy.

    Also, as I mentioned at the end of my original post, existing house wiring is often pretty bad. 500 MHz max frequency splitters , lots of RG-59, etc. My local Comcast is an 860 MHz system and they put all the good stuff up top. The analog stops at 500 MHz and you may be disappointed if you buy a TiVo HD and try to get the digital channels.

    I've previously recommended that people get the cable company to install an HD DVR for them. A side effect of that is the cable company will upgrade the wiring for free. Then, once you are tired of the crappy human interface on the DVR, you can return it and play cablecard roulette with your replacement TiVo HD.
     

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