IMHO I think we already hit the HD PQ low last year when they went from 3 mpeg2 channels per qspk transponder to 4 (~18 months or so ago). Since then all HD transponders have been upgraded to to mpeg4 8pspk turbo. I have not seen DISH HD look as good as it is now since DISH had 3 mpeg2 8psk channels per transponder a few years back.
It's true, adding more MPEG-2 HD channels became unreasonable without adding more capacity, and the switch to 8PSK back in 2004 and well as all HD channels being H.264/MPEG-4 now has helped a great deal. However, just as there was a limit to how much they could get out of MPEG-2 before HD equipment upgrades were needed, there is a limit with the MPEG-4, and they have already been sitting on the edge of that limit for a while now with some channels.
highdefjeff said:FEC schemes all require a minimum amount of signal to work. And if your signal is too low, or if there is too much noise vs. signal, it can cause slow data (low bitrate) which limits the ability of forward error correction (FEC) to be able to even do what it is supposed to.
Ahh yes. FEC schemes is one of the items I couldn't think of.
On 110W, 7/8 seems to be used for all of the national QPSK transponders (32Mbps) which is the best QPSK mode available as long as you have a strong signal, and the sat at 110W is new and healthy so all signals are strong. For the 8PSK transponders (for HD) on 110W, the 2/3 (40Mbps) mode is used, which provides the lowest bitrate but is necessary because 8PSK signals are more sensitive to signal disruptions than QPSK. The satellite at 119W is somewhat old and weak, so the code rates for QPSK are mostly 3/4 (28Mbps) for lower transponder numbers and 5/6 (30Mbps) for higher numbers.
As for low signal affecting picture quality, it certainly can be true if you just barely have a watchable signal so that you have blockiness and audio breaking up. Very easy to do if you plant your dish in front of some leafy trees that the wind breezes through. If you're talking about the signal being lower due to a code rate increase, then you would expect better picture quality since the transponder would have more capacity (as long as your signal remains good enough to have a picture of course). Other than that, the signal being higher or lower cannot have an impact on picture quality because the FEC only provides the equivalent of redundant data, not additional data.