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A real brain teaser from my Direct TV system

  1. Jun 6, 2004 #1

    Ivan Seeking

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    I have nearly exhausted all explanations, and tech support ran out of options long ago, and I can only guess at what is happening here, so I am passing this along as a good brain teaser if nothing else. If anyone knows a solution that would be great as well.

    We have Direct TV and a two TV system. So, two transducers are at the dish - one for each TV. From there, two separate RG6/U coax cables go off in two different directions. One side makes about a 200 foot run, and the other side makes about a 450 foot run. I think 300 feet was the official maximum that was gauranteed to work. The longer run has an unpowered in-line amp installed about at the midpoint.

    Here is the problem, at about noon, and between 4 and 5 PM, the long run loses certain channels. The signal strength for those stations is indicated as zero. It is not unusual to lose specific channels due to certain programming issues with the Direct TV box, but this is ruled out. I have tried switching the two boxes and the problems remains with the long run. I have also tried reversing the transduces at the dish - with the rightmost, then leftmost xducer tried for the long run. The problem remained with the run.

    The fact that we only lose about 10 channels out of maybe 30 or so main stations indicates to me that the TV and the coax is fine. I see no kinks or pinches and it ohms out fine. The line amp is needed in order to get any signal at all. Also, the indicated signal lever drops from about 50% to zero with nothing in between. The DTV people tell me that this is because the indicated signal level is not really a signal level. This really respresents something else; or the tech didn't know.

    The angles of the sun at these times of day would seem to have no bearing on the situation. Nothing jumps out as a likely angle that would swamp the signal uniquely. Finally, the short run never has this problem.

    Almost forgot: First, shorting the coax to gnd to discharge any residual static charge does not solve the problem. Tsu has noticed that by constantly jumping to and from a missing station, it can usually lock on the station after several tries. Finally, if I set the TV on the short run to a channel lost by the other TV, the missing channel comes back. So, sympathetic resonance at the transducers appears to be helping to lock the signal on the dropped run.

    Efforts at blocking the sun seem to make no difference but this does seem to be related to the sun. The problem has persisted for two years but only from about June until Sept or Oct.
     
    Last edited: Jun 6, 2004
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  3. Jun 6, 2004 #2

    Cliff_J

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    Odd. Here's what I know from when I installed these back when DSS first hit the market. Some of it might very well be misinformation as it was what I was taught on the job, not from any official sources. Read with a big ol' grain of salt. :)

    The receiver sends 18VDC on the cable to power the transponder (LNB) and also happens to power your inline amp. The signals are coming in from two satellites that can be referred to as 'horizontal' and 'vertical' signals by some and 'left' and 'right' signals by others. Regardless it seems there's two signals where one pretty much covers the odd numbered channels and the other the evens. The receiver changes its DC signal on the cable to change which 'set' of signals the LNB it is suppossed to receive. On some of the old dishes, you could hear a click.

    One home we worked on had a problem kinda like yours, one receiver had an issue with some channels sometimes, we assumed it was the receiver. Anyways we put in a 4-way splitter in the attic to add a thrid receiver and problem seemed to go away (i.e. never heard back from client). It seems the splitter fixes each one of the two LNBs to each of the incoming signals and then switches the receivers between those two signals at the switch, not the dish since that's how it was explained and I could hear the clicking at the switch. My assumption was that affixing the LNBs and moving the switch point solved the issue. I don't recall any run over 500ft, but on one of those long ones we used a couple of 2-way 2GHz splitters in front of a couple 4-way switches to run 7 receivers and had no issues besides all the heat created by those original RCA receivers.

    So something like this 4-way might work for you. Only ran into this type of thing once (this was 1995, not too many people using it back then) but it did seem to work that one time. The switch cost much more back then but looked like it worked similar to this one:
    http://www.smarthome.com/7819.HTML

    Cliff
     
  4. Jun 6, 2004 #3

    dlgoff

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    Ivan,

    I bet it's heat related. The temperature of the long coax run changes its length and you get some reflected signal interferance at the in-line amp.

    What about in the winter when it's cold?. Same problem? I guess you might get the coax contracting to cause a simular effect.

    Regards
     
  5. Jun 6, 2004 #4

    Ivan Seeking

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    This really caught my attention. With the understanding that I am as much interested in the problem as I am the solution [I will try the splitter], might the excess line impedance be capable of dropping the signal level from the receiver down to where it calls the wrong set of signals? Could this be an intermittent voltage drop problem?

    We have an option to select one of about 30 transponders for each channel, but this is not really a user option since the set automatically ignores any set option and returns to a default transponder. I assume from your comments that this is what this signal from the box is selecting?

    Is there any confirmation sent back to the box that the correct transponder is selected? Also, I’m not sure how many of these transponders are really used. I know that at least four or five are assigned but it is a huge pain to scan for all that might be used.
     
  6. Jun 6, 2004 #5

    Ivan Seeking

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    I don't think this ever happens in the winter. This is one reason that I suspected the sun for some time- we don't see it in the winter! :yuck:

    The time of day issue does seem to be repeatable without fail so there must be something going on here. Thing is, temp does not seem to be a consistent indicator...unless one particular point in the expansion and contraction of length is where the problems occurs. Maybe a fitting or the amp causes a problem only at a certain point, but this gets a little hard to buy. Still, that HFRF stuff can be mighty ghosty.

    I will ponder now.
     
  7. Jun 6, 2004 #6

    Ivan Seeking

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    Cliff, each time we call a channel, does the box send one pulse, or finite series of pulses that selects the transponder, or is this controlled by the voltage level?
     
  8. Jun 6, 2004 #7

    Cliff_J

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    Did a quick google search, sounds like maybe someone else has ran into this issue before.

    On here:
    http://www.dslreports.com/forum/remark,9510272~mode=flat

    One guy posts:
    I'd bet you'd get a much more authoritative answer (instead of guesses) herehttp://forums.digitalinsurrection.com/forum/forumdisplay.php?f=175.

    With answers like this:
    Cliff
     
    Last edited: Jun 6, 2004
  9. Jun 6, 2004 #8

    Ivan Seeking

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    Many thanks.

    I think we caught the little devil! Ha! :approve:

    EDIT: WAIT! Time of day issues? Hmmm. Still a bit of a mystery there.... :uhh:

    Edit again: So some RG11 or better may fix the problem, as I see this. Do you agree? I must be right on the edge with RG6.

    Keep in mind that I have ruled out a bad LNB or IRD.

    You know, I wonder if my line power is fluxuating enough during peak load periods to cause a slight drop in the output signal level.from the IRD... Air Conditioners! Hmmm. Maybe this is just enough, along with the added impendance in the line, to drop the IRD signal out of range. I guess that would depend on how well regulated is the power supply in the box.

    Note that in the winter, people around here mostly use wood stoves for heat.
     
    Last edited: Jun 6, 2004
  10. Jun 6, 2004 #9

    Cliff_J

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    I'd doubt that RG11 would fix the problem. Plus, its tougher to locate the cable and ends and a crimper big enough (its like 1/2 inch in diameter!). I could very well be wrong, but I don't remember the conductors to be that much larger (assuming the issue is a large resistance from excessive distance problem). I think I have an easier first step.

    I'd also doubt the PS to allow the voltage to drop out of range, but who knows what happens with all that cable? Probably best to create some sort of split piece of coax you could use to breakout the center from the shield and measure the voltages from each receiver at the dish. Who knows what voltage range is acceptable and even with a small amount of current 600ft is going to lead to possibly enough voltage drop to fall outside spec. Then you'd almost need the splitter located closer to the dish to be able to get the necessary voltages to the LNBs without worrying about a voltage drop from excessive cable length.

    I'd say its time to make a breakout cable and get the DVM out to see if that's it.

    Cliff

    P.S. I guess a second person and a walkie-talkie to tell the person to switch channels to get the 13V/18V measurements would be needed too. :wink:
     
    Last edited: Jun 6, 2004
  11. Jun 6, 2004 #10
    Have to tried switching the cables for the TV's. Connect the long cable to the 'good' receiver eliminate the cable itself as a problem? Have you tried using an externally powered satellite amplifier?

    Aside: I was an nuke ET in the Navy on a sub and we started to have intermittent problems with an alarm. All of the electronics associated with the alarm were fine but every now and then the alarm would simply lock in... Eventually I found the problem to be a wire lug terminal about 1/16 of a turn loose. That little bit (I mean real little bit) of play at the terminal would allow the wire associated with this alarm to wiggle into a position causing the alarm when the ship vibrated. Prior to that we all assumed that for one reason or another it couldn't be something as simple as a loose wire. I say this because after this "isolated" incident we had two other incidents where faulty interconnecting wiring was the fault not the applicable circuitry as we first thought. So, never eliminate the cable as a problem until you've actually investigated the cable. Just my 2 cents.

    Do you always lose the same ten channels? Cliff, do you know the signal carrier frequency? I'm pretty sure all channels ride on the same carrier with each channel occupying a small slice of the carrier. Is it an 11MHz carrier or is it in the gigahertz? Anyway, the long run of cable may be causing excessive signal attenuation (more than the un-powered amp can make up for) thus knocking out the channels found closer to the middle of the sign wave (the channels found near the peaks of the carrier sign wave may not be as effected). The DC level within the coax may be uneffected because their is very little current draw by the AC component(the stuff you care about) may be overly reduced.

    The time of day problem 'may' have less to do with a heating effects as with an atmospheric/seasonal/solar interference effect. Outside interference may be reducing the received signal strength which would show on a short run, but may be more prevelent in a long cable.

    Anyway, good luck hope you get you TV all squared away.

    [edit] I asked the question about carrier frequency because I believe CATV uses an 11MHz signal carrier. I was unsure it the receiver itself converted the signal to a lower frequency or not. In retrospect I don't think it does so the carrier should be the gigahertz range.

    [edit][edit]I missed where you already swapped the cables from the recievers. If I were a betting man I'd say the problem is signal attenuation.
     
    Last edited: Jun 6, 2004
  12. Jun 6, 2004 #11

    Cliff_J

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    Nope, in the dark on the carrier but the passive 2-way splitters need to pass DC (for LNB power) and be rated for GHz. I don't believe the LNB does more than simple amplification and a HP filter on the signal before sending it on to the receiver.

    I'm guessing on the DC side of things, the signal attenuation should retain the same effect all the time, not intermittently. 'Cause if the LNB was occasionally not getting the proper 18V to switch over to the 'even' ones the receiver would show zero signal.

    Cliff

    P.S. I do remember something about flaky behavior below 60 on the indicated strength too. I get like 93 on mine and still have a dropout during a rainstorm once every couple months.
     
  13. Aug 4, 2004 #12

    Ivan Seeking

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    Well, it looks like a bailing wire and bubblegum solution is in order. The fact is that I'm way beyond the indicated limits and the thing is flakey as hell. It is clearly a simple issue of too much distance.

    What I am doing instead is to send both signals to my office and then retransmit the audio and video for the house side up the hill via cat 5 that I already have in place. Luckily I left lots of extra pairs which have come in handy. I wanted to go with a UHF transmission up to the house but I couldn't find anything sold that is good beyond 300 feet.

    Then, I have to re-xmit the IR remote control signal from the house to the Direct TV controller in my office. Is is about a 450' run but the system is rated as good to 500'. I still may have to make the IR re-xmitter myself as the perfomance limits for this were a little sketchy. This should be simple to do if that's the case - back over the CAT 5 in a pinch I guess.

    This is what I'm going to try. I'll let you know how it works out.
    http://www.accessorywarehouse.com/shop.html

    [​IMG]
     
    Last edited: Aug 4, 2004
  14. Aug 4, 2004 #13

    Gokul43201

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    Haven't read through all the discussion here, but you might be having a problem driving capacitive loads. This doesn't explain the 'time of day' relevance but you could try a different op-amp or put in 2 instead of 1.
     
  15. Aug 4, 2004 #14

    Ivan Seeking

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    It seems to be more with the signal sent back to the antenna that selects the correct transponder. I considered breaking into the DTV circuits to provide some interviening signal management but this sounds like a pain in the butt to me. I always opt for off-the-shelf solutions whenever possible. For a little over a hundred bucks this seemed pretty reasonable. The only question in my mind is the video quality to be expected.
     
  16. Aug 4, 2004 #15

    Ivan Seeking

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    Well I just found a much better but more expensive option. Still, this is the one I think - this is cool. $270 but cool. It comes with the remote IR built in!

    Oh yes, the other unit is discontinued due to customer dissatisfaction.
    This unit seems to hold up well according to a few telephone conversations; and considering the complete 2 year warranty. My expectations are high since they guarantee DVD quality video.

    Features
    Audio/Video distribution over low-cost un-shielded twisted pair wires
    Up to 1000 ft. distance
    Up to 16 receivers for multi-point distribution
    CD-quality stereo audio signals
    5 MHz video bandwidth (-1 DB) for high-resolution, DVD-quality video
    Advantages
    Eliminates ground-loops, noise pickup, and hum
    Broadcast quality video reproduction
    Much higher quality than long-distance coax
    Uses low-cost, multi-function category 5 cable
    No adjustment or alignment necessary 0-1000 ft.
    Superior quality over multi-bundled coax and long runs of speaker cables
    Applications
    Home Theater audio/video distribution
    Remote video extension to bedroom or den
    Send DVD, laser disc, VCR, or DSS output to remote rooms
    Broadcast studio video distribution
    Video extension for remote monitors
    CCTV and security video distribution
    Video delivery between buildings
    Remote camera video monitoring

    more information on this page.
    http://www.wireless-experts.com/pragmatc/cats-av.htm
     
  17. Aug 4, 2004 #16

    Ivan Seeking

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    I don't mean to beat this to death but I wanted to add this. While doing some last minute checking on the company that makes this system - Pragmatic Communications, Inc - I found that they seem to be a bit of an industry sweetheart. In addition to a slew of excellent references I found this from a NASA site.

    http://nctn.hq.nasa.gov/innovation/Innovation42/CompositePipe.html

    If you need this sort of technology, Pragmatic seems to be a real leader to check with when pricing systems. They seem to be quite exclusive. I will post if I find otherwise and I'm putting curses on their company. :biggrin:
     
    Last edited: Aug 4, 2004
  18. Aug 12, 2004 #17

    Ivan Seeking

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    The system is now temporarily installed and tested. It works extremely well and I couldn't be happier with it. I highly recommend this product for anyone wishing to xmit audio and DVD quality video between 100 and 1000 feet. Unlike some cheesy competetitors who claim a two wire system, this system requires all four twisted pairs in the Cat 5 but the video quality is excellent, and the remote control IR retransmitter works like a champ.

    I have been fighting this problem in one way or another for nearly two years. Finally!!!
     
    Last edited: Aug 12, 2004
  19. Aug 12, 2004 #18

    Cliff_J

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    Glad to hear it worked out and that the product works as advertised.

    Cliff
     
  20. Aug 12, 2004 #19

    Ivan Seeking

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    Thanks for your help.
     
  21. Sep 6, 2006 #20

    Ivan Seeking

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    We recently upgraded and the new direct TV IR system uses a different carrier frequency. Direct TV can't tell me what it is, so I need to determine [measure] the new carrier freq so that the crystal in the re-transmitter can be matched. Then I have to send the unit in for modifications. :grumpy:

    The folks at Pragmatic have been wonderful. One can't ask for a better company or product.
    http://www.wireless-experts.com/pragmatc/cats-av.htm

    Pragmatic hadn't seen the new DTV equipment yet, so no fault of theirs. They offered to take the new box and make the measurement themselves, but since I have a good scope there is no need for the additional delay.
     
    Last edited: Sep 6, 2006
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