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Old 12-27-2008, 08:18 AM   #15
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Can you use a coax splitter to drive two receivers? The coax from the dome carries the satellite signal (all channels) to the receiver, the receiver selects the channel desired. 02 38FDDS
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Old 12-27-2008, 09:28 AM   #16
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<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by historyljc:
Thanks Jim,
I don't know that I need the dual INB as we just have regular Direct TV. I believe it all comes in on 101. When I do my search, I show a signal on 101, 110, & 119. I have the low profile unit, but it takes its own sweet time finding a signal. Sometimes it's a couple of minutes and sometimes it's "awhile". Mine seems to have a problem locking in on the satellite. If I don't watch it and turn it off when I start receiving a good signal, it'll wander off and keep searching. Think I'll just wait until we upgrade to HD and go with a MotoSAT. </div></BLOCKQUOTE>

We had the same problem after receiving DirecTV's new receiver upgrade. Talked with Kingdome and they said for it to tune in you have to be on the signal strength screen with one transponder and one satellite selected. They recommended transponder 19 because it is available throughout the US. This will keep the receiver from changing voltage to the LNB, which would otherwise confuse the Kingdome. The Kingdome technician stated that the problem with the newer receivers is that the voltage is changing going to the LNB when powering up.

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Old 12-27-2008, 09:40 AM   #17
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Mike,
Thanks, I'll try that.
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Old 12-27-2008, 10:04 AM   #18
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<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by RedHotSoup:
Can you use a coax splitter to drive two receivers? The coax from the dome carries the satellite signal (all channels) to the receiver, the receiver selects the channel desired. 02 38FDDS </div></BLOCKQUOTE>

No you can't. Only half the channels are on the coax at any one time (CW or CCW polarization). The receiver tells the LNB whether it wants CW or CCW by setting a DC voltage on the cable. A splitter messes that up. At best, one receiver will always win. At worst, neither will be able to do it.

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Old 12-29-2008, 02:33 PM   #19
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<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">joe </div></BLOCKQUOTE>
I sure don't understand that. On my house I have one DirecTV dish with two LNBs on my roof. Coax cables are routed into my attic to what looks like a splitter. That splitter then feeds two coax cables to two receivers (a DVR and a regular receiver) to different rooms of my house. (38FDDS)
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Old 12-29-2008, 02:53 PM   #20
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<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Coax cables are routed into my attic to what looks like a splitter. </div></BLOCKQUOTE>
They do "look" like splitters but they are actually a di-plexer. What you can't see upstream inside the antenna itself are cables running to a special switch which allows this operation.
It's confusing, but it's true. You simply cannot take the feed from one single coax output and do anything with it other than power one receiver.
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Old 12-29-2008, 08:02 PM   #21
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I don't get many chances to correct Bill, so I'll take em when I can get em.

What he's referring to is really called a switch (multi-switch to be exact). A diplexer is another widget that looks similar, but it's used to combine (and split) different frequency signals onto the same cable. Usually it's to combine an antenna signal and a sat signal on the same cable, to go to a TV/receiver where there aren't enough cables to do it individually. Really useful when you have a big multi-switch (8 or more ports) which also has a built in diplexer.

Here's the gory details on the LNBs and switches. This applies to older DirecTV and Dish hardware. There are additional wrinkles with the newer stuff, and it's different between the vendors.

The satellites transmit (up to) 32 different beams from each satellite location, on 16 frequencies. They can double up on frequencies because half of the beams are clockwise (CW) polarization, and half are counter-clockwise (CCW) polarization. Each LNB can only receive one polarization at a time, and the receiver tells it which to do with a signal on the coax going to the LNB. Most of the LNBs you see are "Dual LNB"s, which means there's actually two in there, which is why there's two coax outputs.

Each coax can go to a different tuner (two receivers, or a dual tuner PVR type), and everything is fine. Each tuner can command it's private LNB to whatever polarization it wants depending on the channel it's trying to tune in.

Now, suppose you want to add tuners. You can't split the coax, because the tuners will fight with each other for control of the LNB. Enter the multi-switch. There's two inputs on the switch, one for each LNB. The switch will lock one input to CW polarization, and the other to CCW polarization. There's multiple outputs, usually 4 or 8. Each of those outputs will be connected to a tuner. When the tuner sends the signal up the coax to the LNB, it only gets as far as the switch. The switch connects that tuner to the appropriate LNB, depending on which polarization it's looking for. Internally, the switch is also a splitter, in the (common) case where more than one tuner wants the same signal.

The newer DishPro stuff does things a little differently, by stacking the signals onto the cable, so you can get both polarizations. But that requires special LNBs with the built-in stacker, or an external stacker (and de-stacker) on each end. Then, there's special 4 input switches for the 101/101/119 three LNB head that DirecTV used to use.

The new DirecTV heads that do both Ku and Ka do things a little differently again, and I haven't researched the details. I know they have 4 outputs, and there are 4 input multi-switches for them, so I think they do things very similarly.

Saydiver just asked me if I was writing a book. I guess so.

joe
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