stupid directv

Dear Lazyweb, tell me how to make my damned satellite dish work again. What I used to have, that worked, and then suddenly stopped:

    Dual LNB → 2 short coax →
    uS575 Stacker → 1 short coax →
    uAL DBS Line Amp → 1 very long coax run from roof →
    HR PI 10-2150 MHz Power Inserter → 1 short coax →
    D575D Destacker → 2 short coax →

I think all that junk was ordered from here. The ones I have/had appear to be this and this. I believe that both the LNB and the stacker blew up. I got a new LNB, same model. I can make it work in single-LNB mode:

    Dual LNB (new) → 1 very long coax run from roof →
    DirecTivo (old)

I get strong signal on all transponders. Then I replaced the stacker. The new stacker (looks different, but possibly the same model?) came with a new power inserter, resulting in this setup:

    Dual LNB → 2 short coax →
    uS575 Stacker (new) → 1 very long coax run from roof →
    HR FPI 2-2400 MHz Power Inserter (new) → 1 short coax →
    D575D Destacker (old) → 2 short coax →

I get signal on all transponders on both LNBs, but the signal on the even channels is too low (under 40%) and as a result, "guided setup" won't complete. So clearly I need amplification on that long run when the stacker is involved, like I had before. So I put the old amp back in:

    Dual LNB → 2 short coax →
    uS575 Stacker → 1 short coax →
    uAL DBS Line Amp (old) → 1 very long coax run from roof →
    HR FPI 2-2400 MHz Power Inserter (new) → 1 short coax →
    D575D Destacker (old) → 2 short coax →

This doesn't work. I get no signal inside. My guess is that the amp is eating the power before it gets to the stacker, and so the stacker doesn't turn on. Why the old stacker worked, I don't know.

Can someone please tell me how to make this go?

Also, explain to me how these line amps work, because the fact that the amp goes at the head end but the power gets inserted at the tail end kind of makes my head spin.

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14 Responses:

  1. autopope says:

    I love the way that the home TV set has slowly morphed from a solitary box sitting in the corner of the living room into a fearsome mass of 19" rackmount components and computing hardware that baffles and enrages engineers ... but there's still nothing worth watching on any of the channels!

  2. solarbird says:

    Is there any reason to think that the uAL DBS Line Amp did not blow up? Because that would be my first thought.

    You could test functionality by ditching everything but the even-channel LNB, the line amp, and the directivo, and compare even-channel signal strength against the level recorded after your second-to-last attempt previously (showing 40%). (I assume here that the line amp does not require some sort of signal conversion previously provided by the stacker.)

    If it is working, then could you put the line amp on the even-channel LMB only, before the stacking? If only the even-channels are below minimum signal level, it seems to me that amplifying the combined signal isn't important - you could just amplify the even-channel side first. (Again, assuming as above.)

  3. sherm says:

    I would ask this lazyweb - more of the kind of geeks you're looking for.

  4. magicpacket says:

    I work indirectly for DTV, and deal periodically with satellite wiring, but it's all fancier stuff (5-LNB dishes, etc). So I can't give you details on the hardware you're using, but I can expand on the general concepts.

    On your dish, both the "odd transponder set" and the "even transponder set" should be in the range 950-1450 MHz, and which one gets delivered by the dish to whatever component is attached (each input port of the stacker, in this case) is determined by the receiving component, which sends either 13VDC or 18VDC up the line. The dish uses the voltage as a selector, and it also draws whatever current it needs off that voltage to do its magic. So the stacker tunes one of each set, then does some analog magic to fit everything in to some range, presumably 1GHz wide, probably 450-1450 MHz (check the specs).

    The destacker then reverses the magic, and provides two outputs, presumably which behave as multiswitches. The DirecTivo drives each one with either 13VDC or 18VDC to select what it wants, and that voltage will also be used by the destacker to run its electronics.

    So the question is how to get power to the amp and to the stacker. The power inserter is rated as 2-2400 MHz, but that's talking about the signal range that it passes. It's also pushing VDC back on its input. That power should theoretically run the amp, and get passed through to run the stacker.

    I wonder what voltage the old PI used, and what the new one uses. Perhaps that switched from 18V to 13V. Presumably the neither the amp nor the stacker has a transformer, so they need to be fed 18V so the stacker can drive that to the LNB (though that can be easily stepped down to 13V with a regulator). Then again, you got 40% when you took out the amp, so maybe I'm wrong here.

    Does that at least answer your last question?

    • gryazi says:

      The stacker stacks two LNBs that see different birds, right?

      And each LNB has switchable polarization based on voltage supplied, represented as odd/even channels?

      And even channels are mysteriously low vs. odd channels?

      I'd assume it would help to test near the dish/without the stacker, which is not easy.

      Perhaps you can test with only one LNB, without the stacker/amp/variables, to see if even/odd on that LNB's bird magically snaps back to equal signals.

      Perhaps that polarization on both LNBs is sort-of-fried == replace LNBs, or perhaps it is just sort-of-biased/misbiased by the new power inserter (so we're back to comparing voltages).

      Or, relatedly, perhaps the new stacker is not putting the right signals on its input side to the LNBs Since these are meant to live with power inserters/etc (as your old one did), perhaps the destacker senses the demand from the receiver and encodes that somewhere harmless as a signal to the stacker to do the right thing -- and this new pairing is somehow incompatible, or the new stacker is just sorta defective and not pushing the LNB polarization over enough to get a good signal on that polarization (voltage drop?). (How the heck do the LNB-feedhorn combos work to achieve that selection? Electromechanically? Signal polarization, as far as reception is concerned, is normally a physical property requiring reconfiguration of the antenna == feedhorn, or switching between two separate antennas therein. I think DirecTV is circular left/right; for systems with linear polarization, quite often a tiny little antenna in the feedpoint literally flops from vertical to horizontal and back.)

      And finally, perhaps the amp is just toast / has become far too noisy from exposure/component failure.

      If my assumptions are wrong and even/odd channels are interleaved between LNBs, not by polarization, this is probably not helpful.

      • magicpacket says:

        It doesn't actually matter if his dish is a single or dual LNB, because those look the same in the DirecTV world. If it's a dual, then there are two combiners (one for each polarity) in the LNB, before the 2x2 multi-switch which is in there anyway. There's no way to try just one of the two LNBs.

        Yes, DirecTV uses RHCP and LHCP. The antenna in the LNB receives both simultaneously (don't ask me about the physics) and has two different outputs. Then there are the two outputs from the second LNB, and those of like polarization are combined into a single odd or even set of transponders.

        I would next try replacing the amp. Possibly with a dual-channel amp to be inserted before the stacker, if you can find a weatherproof model that doesn't require an additional input for power.

        • gryazi says:

          Diagrams would be worth 142 words here, I should look some up.

          Isn't it kind of fishy that the signal strength of one polarization is significantly crappier than the other, then? If the [DirecTV-LNBs-and-feedhorns-module-dingus] has one output per polarization, and those are what are being stacked by the stacker, that sounds like reason to suspect the stacker, or at least to make sure said on-dish-module isn't toast besides.

          (Especially since common mini-dish parts are effectively free, given how many people never install stuff and give up and put it on eBay, versus things like line amps that cost money and may or may not actually function.)

          Wouldn't putting a dual-channel amp between dish and stacker potentially require power to be inserted up on the roof (between amp and stacker), assuming the stacker when functioning normally is going to be trying to provide the right signals to the LNBs? Because at *some* point in the chain any excess injected power has to turn back into the [on-dish-module-dingus] control levels before it reaches same, yes?

          • magicpacket says:

            Well he didn't say what the signal levels are on the odd transponders in the dish->stacker->PI->destacker->Tivo setup, and 50-60% would be far different than 90%. However he did say that when he uses a single run of coax from the dish straight to the Tivo he gets strong signal on everything, so the dingus is probably fine.

            Also, note that it's not at all a signal level in the traditional sense: it's a composite number based on a bunch of stuff, but it really comes down to bit error rate. So "40%" could mean not much signal, or lots of noise (such as from a long cable run).

            I said to suspect the amp because when that's in the mix with the new stacker he gets nothing, so I'm suspecting the amp is eating all the power.

            I'm assuming that both the stacker and the amp run on the same voltage that drives the dingus. OTOH, I've never actually seen a weatherproof dual-channel amp, only indoor models.

  5. a_0001 says:

    Any RF amplifier (operating under reasonable conditions) increases the level of both signal and noise, so it's best to have the greatest possible signal-to-noise ratio at its input. In your system, this is found closest to the LNB, before the signal (but not the noise, much of which is in the amplifier itself) has been attenuated by the long run of coaxial cable.

    Since there isn't usually power available outside where the amplifier and LNB are installed, it's convenient to send the power out along the same coax that carries the RF signals in the opposite direction. Sure, there will be a little power lost due to the voltage drop in the cable, but it's easy to overcome that with a higher DC supply voltage. (Separating the power and RF is easy -- remember that a capacitor is an open circuit to DC but will pass RF just fine.)

    The first thing I'd check is the DC voltages at the RF input and RF output terminals of the line amplifier, with everything else connected in the last configuration you've described. It's possible the line amp has failed and is no longer passing DC to (or RF from) the stacker. It's also conceivable, but not likely, that your new power inserter can't provide enough power for all of the amplifier, stacker, and LNB.

    • jwz says:

      So here's another theory that just ocurred to me: maybe the old stacker was able to work without external power, whereas the new on cannot. so in the old setup, the power inserter was only for the amp.

      But I guess I'm not certain that the old amp is functional beyond providing continuity.

      • magicpacket says:

        There's no way the stacker and the LNB were both able to work without external power before.

      • a_0001 says:

        No stacker, and certainly no LNB, will work without external power. (Your IRD--DIRECTiVo--can also provide DC power, but just for an LNB.)

        • jwz says:

          Obviously not with no power, but perhaps the old stacker worked by leeching from the power DirecTivo uses to drive the LNB. Meaning, maybe the old stacker worked without the need for the HRPI.

  6. ch says:

    you didn't say which directivo you had, but the old boxes had a common failure mode that killed one of the tuners and sometimes both of them. the even channel lossage is a sign that one of the tuners is unhappy. try it in single feed mode -- that will cause the one tuner to switch back and forth. if it works, your feed is fine and you've got a blown tuner and a refurbished tivo is called for. (you can transplant the drive.)

    re: the head spinning, the bias on the line is just that. it is common with LNA's or inline amplifiers in microwave applications. you have to make sure that any devices you place between devices needing bias and the bias tee (what you call a power inserter) are designed to pass dc through them. passive devices (mixers, splitters, lightening arrestors) should be checked carefully to see if they pass bias. other than this, it doesn't matter where you place the bias tee.

    note that the bias on directv dishes not only powers the LNB/LNA, it selects the polarization of the receiving element. if you want to view/record channels on opposite polarizations, you either need two pieces of coax or the stacker set up you have.

    (apparently some of the newer STB's are stacker compatible and don't need a destacker. directv finally got a clue on that one.)