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1149 posts

Uber Geek


#62592 10-Jun-2010 13:59
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[Mod please move this if it is not the right place for it.]

Hi all

6 months or so ago I decided I wanted to upgrade my satellite setup to get both polarities of Optus D1 and D2, and Intelsat 5 if it was possible. The results of this decision so far have meant nothing but headaches for me! In short, the multiswitch and dual output LNBs I bought didn't seem to want to play ball with my HTPC. I thought they either didn't provide enough signal or compromised the signal quality (...or that I had wiring issues...or that I had dish alignment issues...or that I had received faulty LNBs...or that I had driver problems......the list of what I have investigated goes on, but you get the idea), and I have been tearing my hair out trying to get to the bottom of the issues. The worst thing about it has been that the issues have been inconsistent/confused and I haven't had the time, tools or knowledge to really troubleshoot the problem/s properly. It's a long story so I won't bore you with the details. Suffice to say that I think I have finally found the source of the problem: my HTPC TV card's output voltages.

The HTPC is putting out approximately 14.5V for vertical and 20.5V for horizontal. As you might guess, the vertical voltage is smack bang in no-man's land for the dual output LNBs (spec: 11.5-14V and 15.5-19V for vertical and horizontal respectively). The resulting symptoms were severe dropouts on vertical transponders probably caused by the LNB switching between vertical and horizontal or being unsure which polarity to supply. There were also occasional glitches on horizontal transponders (worse on high frequency transponders), but Freeview channels especially on 12456H were absolutely watchable. As far as the multiswitch goes, it is unclear what the input voltage specifications are (output is perfectly within spec so other STBs are usually okay) but I'm guessing the same issues apply because the same symptoms can be observed. The clincher is that when you plug in other LNBs with looser/different input voltage specifications you get perfect reception. For example, a Zinwell ZKF CH21 gives *almost* perfect reception with a glitch every minute or so at most.

As you might imagine this has led to the almost perfect storm of confusion because none of the symptoms made sense. Some LNBs work fine, or one polarity works *almost* perfectly etc.

My question: is there a way to [safely] reduce the output voltages of my TV card?

The first thought that came to me was to insert a resistor inline with the HTPC between the card and the multiswitch, but I'm not sure if this is appropriate given that it could cause impedence mismatches. I'm also not sure what value I should use because I'm not sure of what current the TV card is producing.

Ideas and suggestions would be much appreciated!

On a different front, this gives me cause for concern about my other PC components. I mean what if this issue is really caused by my power supply voltages being too high (or even out of spec). If this is the true cause, is there anything I can do to "fix" it?

Thanks in advance :)

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57 posts

Master Geek

  #345396 25-Jun-2010 21:47
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I would like to continue on the discussion about H and vertical polarisation of the LNB. I have a sky star card in my PC for recording and for some reason have not been able to tune anything vertical.

I have Lounge sat reciever only watching Horizontle, Bedroom receiver watching vertical and Horizontle, and of course the PC that is set horizontle.

We all know that Horizontle rules and I was having to unplug the sat wire from the other two to recieve vertical on the third.

Now I like to experiment so i cut the RG6 just as it enters the receiver in the Lounge and also on the PC, and Installed a switch,, the Idea was to switch the dish connection out of the picture instead of unplugging all the time.,,,  Now what I found was that it worked well,, but I also found that by leaving the switchs off,, the sat recievers still receive a good signal, but dont send the voltage up the line, so I can watch vertical in the bedroom set at night..... The only problem with this system is that when the bedroom set top box is recieving vertical, it takes out the horizontle on the other two sets.  I have to be carefull here.

Hey but I bet there is a better way!!!

The next thing I would like to try is,,,,, can a LNB that is set to Horizontle be turned 90 degrees to recieve vertical.,, You see what I am getting at here,, I would set up 2 dish and feed them through a splitter down the line so that there is still only one voltage ,, does this sound right...?? 

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