Thank you for the feedback regarding the changing SD/HD picture you're seeing at home.
WKBD carries primarily upconverted standard definition analog video that is mapped into the HD transmission (1080i) standard. The only programming that we broadcast as full high definition consists of 1) the Paramount "Enterprise" program on Wednesday evenings at 8 pm, 2) the UPN Friday night movie is usually, though not always, a high definition feature, and 3) one weekend movie a month from a special HiDef movie package that WKBD purchased some time ago. The Sunday rebroadcast of the "Enterprise" episode seen on Wednesday night is not done in HiDef, but is merely an upconverted analog version of it.
I'm not sure what leads you to believe that your receiver is randomly switching between HiDef and SD since I'm not familiar with the Motorola box or the Voom satellite package you speak of in your email. Is the Voom service provided by someone else? If so, who?
It's hard to provide you with good, hard answers on something like this because several players are involved. First, WKBD's HiDef channel on air ALWAYS runs a HiDef 1080i encoded video data stream. It cannot switch between the two modes. Secondly, while we provide a HiDef transport stream to our transmitter does not mean that the program is originating in a High Definition format. As I outlined above, any programs other than those specifically mentioned above are upconverted from a 525 line interlaced analog format known as NTSC, the same color system that's been in use in this country since the early 1950's. The upconverter first digitizes the analog video, then performs a lot of very complex operations to reduces noise and grain in the original analog signal, then provides remapping on the approximately 480 lines of active video into the 1080 lines of the HiDef picture space. This generally provides a fairly low data rate signal to be sent to the digital encoder which prepares the data for broadcast over the air. The data rate of this signal can occasionally exceed the allowed data rate for actual over the air broadcast, so the digital encoder just mentioned does some massaging of the video data to ensure a constant data rate for transmission. This encoder also adds digitized audio, closed captioning, and a bunch of other ancillary data needed so that the home receiver can reassemble the entire program for viewing. After all this, the signal gets launched into the air via our transmitter and antenna system.
At the satellite company's headend (receiver farm and transmission system), they receive and decode the program just as on off-air receiver at home would. But from here, the similarity ends. Since satellite time and bandwidth costs many tens of thousands of dollars per hour, most service providers cram as much data payload onto a satellite channel as they can. The equipment used to do this is also very complex and constantly evaluates the amount of bandwidth really needed to provide the picture with acceptable (though not optimal) performance. A still scene requires very little bandwidth whereas a scene filled with lots of action and detail requires much, much more. Since we, as broadcasters, have no way of controlling what the service providers do with the data once they get their hands on it, I can't begin to guess what's really going on with your picture. One of the ways digital reception can "fail gracefully" is to reduce the recovered data rate, and hence, reduce the resolution. This may be caused by non-optimal antenna alignment or atmospheric disturbances like heavy thunderstorms. Beyond these couple of things, I don't know what else I could reasonably blame for the problem.
If you'd like to continue this dialog, please feel free to write me describing exactly what you were seeing on the screen, what the weather conditions were at the time, etc. Another question comes to mind. Does your receiver allow off air reception from an antenna? If so, what kind of reception do you get with it? Is your viewing screen shifting between HiDef and Standard Def modes or is it really the receiver that's experiencing this behavior?
I look forward to hearing from you.
