A few questions
1. What exactly is the stack plan? (parking alignment for the sats?)
The sats are so close together, relatively speaking, that as far as the dish is concerned it can't tell the difference.
No the stacking plan is how the signal gets from the dish to your receiver(s). There a couple of basic signals used by the receiver to tell the dish which signal(s) it wants. It start off just sending 13v or 18v to pick between the 2 polarities of the signal which also corresponds to even or odd transponders.
Then when they started using 110/119 they needed an additional signal so they used a 22khz tone and 13/18v to select between the even and odds there. 110 & 119 are combined together at the dish because even together they don't fill up one block entirely.
When they started doing the Ka sats rather than adding more signals they decided to stack more signals on each combination. The Ka actually have 2 blocks at each orbital location so needed 2 slots in the stacking plan. The ka hi and ka lo from 99 are sent the same time as the 101 signal and the ones from 103 are sent the same time as 110/119.
This is also where the bbc comes in. The receiver can't directly tune the ka lo in the stack plan so it activates the bbc when it needs that part and the bbc switches it up to the ka hi portion replacing the ka hi.
The image shows the stack plan as listed in the WB68 manual.http://www.dbstalk.c...=1&d=1215661918
2. Would a new LNB to receive Ka at 101 help?
A new LNB could allow us to receive KA at 101 yes. I don't think they will take that route however. It would require a new lnb which means new hardware and an install scheduled for every customer that has a current hd install. Because of the specifics it would also mean swapping out every old at9 sidecar dish to do it realistically. That's a lot of costs to eat.
3. If D12 is the same as D10 and D11, why only 50 national HD channels and not 75?
My guess for that is it a combination of factors.
1) 200 hd channels is a lot of national channels and by using less capacity for National HD channels they can use more spot beams to provide more Locals to markets they don't have them and add missing local channels in other markets.
2) limits on how much bandwidth they have to use at one slot as national channels. Since d10 and d11 and probably d12 are configured just for ka lo they only have 1 500mhz block to work with. Currently d10 is running 16 transponders but was originally planned for 14 and d11 is running 14. 14 transponders at the size DirecTV is running them ends up using a little over half the bandwidth in the 500mhz ka lo slot. 24 would be the max possible.
Currently we expect once thing settle down we'll have 28 transponders worth of HD channels coming from d10 and d11 for national content. If we had a completely empty orbital slot for d12 we would expect another 14 transponders worth ending up at a total of 42 but we won't be able to do that. When d12 launches I expect some shuffling around of things.
For example D12 ends up at 99. D11 and D12 at 99 running a total of 18 or 20 conus transponders with 4 or 6 left to use for lots of spot running from both sats. (spots can reuse the same transponder frequency because they aim at different areas and don't interfere with each other). D10 running at 103 will then turn off some of it's spot capacity moving those locals to 99 and fire up more conus transponders and be back up 16-18 by it's self.
Net total is 34-38 conus transponders which puts us right around 200 total hd channels with a lot more spots total with more of them coming from 99 than 103. A little shuffling and they get plenty of use from d12 with out a reconfigure and can later in life shuffle things around more to cover failures. It also maximizes their install base of receivers.
If you are interested in more details toms got a great post at http://www.dbstalk.c...ead.php?t=82295
4. What are they backhauling at 101?
Backhauling is a pretty simple idea. DirecTV gets tv signals from all over the us to gather up the locals and from who knows where when dealing with the premium channels and needs to get all of it back to it's uplink centers where it does what ever it needs to and sends them up to the sats to be beamed down to us. It has to get those signals there some how so it uses sats for that process. Backhauling also gets used by other things like news channels. It's how the signal gets from those live reporters back to the studio using a truck with a dish on it.
I see tom snuck in with a shorter quicker response already but I typed it up so I'll leave it here =)