Originally Posted by AndThenScottSays
An inquiring mind would like to know - why is this the case? I don't know much about TV, only radio, and there you can input whatever, wherever you well please.
Unlike the other networks, FOX provides a network HD signal that is ATSC ready (actually it is a pre-encoded 15mbps ASI signal, but for simplicity, lets just call it ATSC) meaning the signal that comes out of the receiver can be directly put into the ATSC digital transmitter unlike the other networks who require decoding the signal back to HD-SDI (1.5 Gbps) to run through the Master switcher and then encoding it to a 15-18 mbps ATSC signal (an ASI signal FOX already provides to stations) and then on to the transmitter.
The FOX Network ATSC ready signal is inserted into a splicer that is located as close to the transmitter as possible and takes the stations ATSC signal (after the switcher and encoder) and then removes the local stations picture and sound and "splice" in the network picture and sound into the signal (not switched as with the other networks).
Since HD Master controls use a signal call HD-SDI, that isn't compatible with ATSC, you have to drop back to SD (that is the only SDI signal FOX gives us) through the switcher.
The purpose of doing it this way is that more stations can run HD network programming (i.e. NFL and NASCAR) without having a HD plant. The drawback is for the stations that run full HD Master controls, it limits what they can do when network is on line.
And that is how it works.