What is this 'mapdown'? Is it simply mirroring a channel elsewhere?
Yes. Essentially a channel somewhere else in the line-up has a tag that tells the receiver to show it on another channel on your EPG.
If so, why do they even send HDs in the 9400's? Why not just send them to the actual lower channel, like 105 or 109?
Software issues. The receiver can really only make out one "real" channel per channel number. If the HD channel and the SD channel were on the same channel number from the satellite, the receiver would crash like Richard Petty at Daytona! This was tested not too long ago on some PI channels for a few days and it was ugly.
And while I'm at it, why even leave the SD channels there when there is an HD channel? If I sub to only an HD package, will I still see those darned SD clones?
Two reasons pop to mind right away.
1)not every TV in the house is HD for most folks and some have a mix of HD and SD tuners in their homes.
2) Less room to record a program if it's not terribly important or if it wasn't HD to begin with.
And the most important reason for me is to eliminate "Stretch-O-Vision". Any program is stretch-o-vision will trigger an innate reflex causing me to change the channel! If I have an HD counterpart, I can still watch the program in OAR.
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A little review on terms:
Mapped Channel:
A channel has a tag that makes the receiver put it on another location. The mapped channel numbers do not exists on the satellite EPG or system tables.
--Local channels are "mapped" to their local channel numbers.
--HD channels are "Mapped" to their SD counterparts' channel number
Mirrored Channel:
A channel is placed on two different channel numbers directly from Dish. A mirrored channel can also be mapped.
--USA Network HD is uplinked to channels 4105, 5328, 5502 and 9431. Every one of those channels is really the same video stream at 110° transponder 17. So we way USA Network is mirrored on channels 4105, 5328, 5502 and 9431. There is no wasted bandwidth here.
--Channels 5105 and 9431 are MAPPED to channel 138. The other two aren't mapped at all.
(9431 "Home", 5502 AK/HI HD pack, 5328 Dish Latino MAX HD, 4105 "Mystery Pack")
Duplicated Channel (sometimes referred to a "mirrored satellite")
A channel is placed on the same channel number on two different satellites such as 61.5° and 148° or 61.5° and 129°. A subscriber is never supposed to see both satellites at the same time.
---Most HD channels are at 61.5° and 129°. This has to do with "look angle".
See ya
Tony