Wanted: Answers to Antenna Install

Discussion in 'DirecTV TiVo Powered PVRs & Receivers' started by Maddod-99, Jan 8, 2006.

  1. Jan 8, 2006 #1 of 11
    Maddod-99

    Maddod-99 New Member

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    Jan 8, 2006
    See if you can help solve this brain teaser:
    Luckily, you will only have to read it & not go up & down from my hot/fiberglass filled attic to get an answer!

    I recently bought a TV-55 Terk antenna for local OTA HD signals.
    I have a HD Tivo DirecTV Box (Integrated/300 hour) w/ ability to attach OTA for local HDs.

    Antenna is mounted in the attic. When I attach it directly to the Tivo DVR it works great.

    Problem:
    I want to drop the signal into my room by diplexing it into the existing sat cable run.
    I use a GHz isolated (One says Sat In, the Other says TV In), power passing, Diplexer.
    I use this Diplexer where I combine the signal (attic) and where I split it back out (in my room).

    BUT:
    Using this configuration,
    When I connect just the Antenna In into the DVR: It works.
    When I connect just the Sat 1 In to the DVR: It works.
    When I connect both: Ant works & the Sat 1 drops out. The box tells me its searching for Sat 1 so no signal is getting in.

    I can play with the cables (in & out) real time & the errors will come, or go, based on the above.

    How do I combine & then split out these 2 signals successfully?
    Can it be done? Am I interfering with some upstream (from cable box) signal (Have no volt meter, cant tell).
    I have used Power Passing & non Power Passing Diplexers. Non Power does me no good, Power gets me to this problem.
    Must I have only a direct line drop & screw combining & splitting out?

    PLEASE HELP
     
  2. Jan 8, 2006 #2 of 11
    JimSpence

    JimSpence Just hangin'

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    Is the diplexer power passing on both legs or just one? I believe it should only be the sat leg.
     
  3. Jan 8, 2006 #3 of 11
    Maddod-99

    Maddod-99 New Member

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    Jan 8, 2006
    Thank you for your quick reply Jim.

    As it stands now, I have BOTH sides being power passing:
    I was told to match them in this manner as both the antenna in the attic has a preamp on it ( to push through the myriad switches & run lengths I have) & the downstairs is power passing (because I was told to match them).

    I am going to take your advice & try the upstairs only as power passing (sat end) & downstairs (box end) as non power passing.

    My symptom as described above seemed like when I completed the circuit with both imputs connected, I was "shorting" something. Total guess on my side though. Will try your suggestion & check back in with feedback.
     
  4. Jan 8, 2006 #4 of 11
    Maddod-99

    Maddod-99 New Member

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    Jan 8, 2006
    after many hours I have solved the riddle to this.
    I have a Dual DC passing diplexer upstairs & a Sat Only DC passing diplexer downstairs. I get everything working together brilliantly!
    Pass this on to anyone who needs to know, took me 2 months to get here, several D* visits to my house & hours on hold. Arghhh
     
  5. Jan 9, 2006 #5 of 11
    TyroneShoes

    TyroneShoes HD evangelist

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    Since it relates, can I bore you with my favorite story? (if not, push on) I'll be brief. Really.

    A city had technical issues with its city-owned power company. No one could solve the problem. They finally called on an old retired guy who helped design the system. He agreed to fix the problem for $10,000. Once the deal was on paper, he took out a wooden mallet and tapped three times on a strategic point, which fixed the problem.

    The city engineer said, "I'm not going to pay you $10,000 for simply tapping on a conduit with a mallet."

    The retired engineer replied, "You are not paying me for tapping on a conduit with a mallet. That part was free. You are paying me for knowing exactly where to tap."

    The city engineer paused for a beat, and signed the check.
     
  6. sailor44

    sailor44 New Member

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    Dec 15, 2003
    texas
    Maddog,

    I have just now arrived at your problem and I see you have found a solution, and I wonder if you could elaborate a bit for me?

    I want to have an antenna mounted preamp, with a power supply in the house, and want to use diplexers at both ends of the sat coax, to save a separate run from the antenna to the sat box. I am now using two diplexers. With these, the sat works fine (so I assume that there is power passing for the sat side) but the antenna gets no power to the preamp. Do you know how to get the preamp working without fouling up the power to the LNBs on the dish??

    BTW, If I locate the power supply and the preamp between the diplexer in the house and the tv input to the sat box, the preamp works fine. This indicates to me that the diplexer will not let any power get thru it to the preamp when it is located up on the antenna mast.

    Thanks for your (or anyone who has the answer for this) help!
     
  7. newsposter

    newsposter Poster of News

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    SE PA
    so directv owes OP 10K right?
     
  8. TyroneShoes

    TyroneShoes HD evangelist

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    Sep 6, 2004
    Something like that
     
  9. TyroneShoes

    TyroneShoes HD evangelist

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    Sep 6, 2004
    There is only one way I could imagine this working, which would be to use diplexors which have no power blocking (or that block only the port connected from the TV to the diplexor, which can be done with external blocks), leave the preamp power supply safe inside the bubble wrap (IOW, don't hook it up) and use a preamp that can be powered by as little as 13 volts. Since the LNBF power must shift between 13 and 18 volts, it is obvious that adding other power sources to that cable could F things up. But since the DVR provides a constant 13-18 volts at all times, that could be enough to satisfy both the LNBF demands, as well as the preamp itself. It somewhat depends also on whether bridging the DC power in parallel with the preamp will load it down so much as to not leave enough current for the preamp, or if that will flummox the multiswitch in the LNBF.

    So that could work. Or not. You need to have compatible equipment, cabling that is not too long, diplexors with the proper blocking and frequency cutoff, and a little bit of luck.
     
  10. sailor44

    sailor44 New Member

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    Dec 15, 2003
    texas
    This all sounds impracticable to me, so I will just stay with what I now have set up. What I did was to simply put the preamp down by the power supply, in the house , next to the tv input. this way the voltage only has to travel about two feet, to the pre amp, and it does not have to travel thru any diplexers at all. This seems to work just fine! Altho I do realize that is it better to have the pre amp up on the mast with the antenna. However, this is to be preferred (at least, by me) over running a separate coax up to the tv antenna

    And, thanks for your input!
     
  11. TyroneShoes

    TyroneShoes HD evangelist

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    Sep 6, 2004
    That somewhat changes things. A preamp is designed to go at the mast, because a preamp is designed to be used where the received signal may be weak, as compensation for that very low signal. In a low signal area, placing a device designed as a preamp at the TV doesn't typically work well, because the signal is much weaker from attenuation losses from the downlead and distribution, so it just amplifies what is a noisy signal into a stronger, even noisier signal. If the signal is not that weak, adding a "preamp" at the set usually makes things worse by overloading the preamp. Adding a post-amp at the set has a similar undesired effect of overloading the tuner front end (many HR10 owners know this problem intimately, even without an amp).

    For ATSC, if you can maintain a s/n ratio 15 dB over the noise floor (20 is more practical as it covers atmospheric variations over time) at the end of the downlead as it goes into the set, you have enough signal and don't need amplification. But if you can't, that means that an amplifier at that location typically also can't raise the s/n ratio, just the aggregate level of both signal and noise (the s/n RATIO stays the same). The trick is not to have a stronger signal, the trick is to have a greater s/n ratio. Placing a preamp at the mast helps that, but at the set, it really can't, except in the rarest of circumstances, and that is usually precarious.

    IOW, if the signal is capable of being amplified directly at the set and that working, it is probably going to work just fine even without an amplifier, as the line amp is electrically very similar to the front end of the tuner, and if one works (either the amp or the front end of the tuner) the other will also likely work. If it doesn't, and a post-amp directly at the set actually helps, that points to a problem with the tuner front end. But the amp can then be a successful workaround, even as rare as that might be.

    "Preamp" refers to amplification before all of the downlead and distribution losses. When an amplifier is used closer to the set it is more accurately a line amp, post amp, or a distribution amp. There is rarely a practical usage for that unless you are running the cabling another long distance after the amp or you are splitting the signal to more than one outlet.

    Also, preamps have a window of operation that will typically accept a -30 to -15 dB signal while the line/distribution amp typically wants to see 0 to 10 or so. The output is also correspondingly higher. That means that there are rare instances where a preamp design might be used downstream effectively, but rarely, and usually not practically. If it works for you (yet doesn't work without the amp), consider yourself very lucky to have gone against system design recommendations and still had success.
     

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