Iceberg,
> But how much of the dish has to clear the roof? <
Most of it.
> If I set it on my deck, about the bottom 1/4 will be blocked by the roof...it sounds like I'm screwed. <
Not necessarily. The bottom 25% (assuming you're talking about a linear portion of the diameter) represents only ~15% of the reflector's surface area, or less than 1 dB of loss. A 10' dish has a lot of gain. I've seen them work with a full quarter panel missing. (The problem there primarily being the extra ground noise pickup from the missing panel.)
I agree with Brian that if you want good stability (and low phase noise) for DVB reception, you should consider replacing the LNB with something newer. If you do, with an LNBF you can control the polarity just like you do with Ku (13/18V), and not have to worry about running wire and driving the servo positioner. As a bonus, the noise temp will drop from 50K to 17K.
- Tim