Originally Posted by TomCat
Where do I get the idea? I get it from reality. Its a fact, unlike your assertion regarding the max bit rate. FOX blew the doors off of that a few years ago. They were at 55, moved to 73, and eventually to 100.
Nope, never went to 100 Mbps. I keep an eye on the Fox engineering website and the info was for the 73 Mbps ultimate rate they were going for. Now that SD is gone, they've dropped back down to ~70 Mbps (just looked).
In reality, no one goes higher than Fox @ 31.25 Msps. But instead of using 9/10 for the FEC, they dropped to 3/4. Most IRDs only go to 35 Msps, though 45 and 55 are out there. Are they practical for broadcast use? No. Just like 16APSK and 32APSK are meant for other professional uses that require even tighter control of linearity at the uplink site. So, in reality, 8PSK using less than 35 Msps is what is done.
You said that networks were delivering at 100 Mbps, which in reality is not true.
Rumor was that the company that used to backhaul the Suns is also at 100 and even tested to 200 just for grins, knowing that was impractical, but they still uplinked at that rate as a way of stress testing downlink sites, so it would be hard for that max bit rate fantasy to hold much water. FOX needs 100 because they will be doing six prime-time MLB games at once, starting in May.
You are correct that the max of 80 that I quoted is not true, with regard to capability, but it is the max that anyone uses for network delivery to affiliates.
I see nothing on the Fox engineering website that indicates they will be upping the data rate on the transponders and adding more streams. They can spread the 6 games over the current mux configurations on the two satellites. Plenty of space as currently configured.
I'll say that the current Fox mu configuration will not change. And I can point either of my two dishes at the transponders and prove it.
The bottleneck is receive; as the bit rate goes up the EbNo, BER, and MER go up, meaning you have to have more robust downlink equipment to receive it. For a TV station doing point to (200) multipoint, that meant 200 receive site upgrades. Which FOX did. The only reason their program streams inside the 100 mb MPTS are 14.5 is because that prevents the station from having to do the SMPTE 310 compression. 80 may be the ceiling that certain downlinks can't reliably receive above, but 100 is alive and well where I live.
Yes, Fox spent a lot of money to get stations going at the 73 Mbps using the old IRDs. Now, with the new Motorola IRDs and the loss of SD, they've dropped the mux bitrate down by using a lower FEC, providing for more headroom.
Point me to anyone that is doing 100 Mbps and I'll point my dish there and look.
So yes, in the case of FOX, and probably PBS, the PQ delivered to the station is identical to what is broadcast. That's actually a good thing; other stations eventually have to compress further to fit into the 6 MHz window, and manipulate the signal more increasing the probability of degrading the signal beyond what the FOX/PBS method does. And I think nearly everyone uses DVB-S2 by now; it's been the standard for a number of years, IIRC.
PBS is no different than ABC/CBS/CW/NBC when it comes to the station taking it and routing it through their plant. The fact that PBS is not doing at least 2:1 really sucks, as I've seen macroblocking many a time with their feed. But, PBS should not be using the sat feed as primary anymore, as they are supposed to have completed the implementation of their IP push delivery system, allowing for very high bitrate H.264 video.
But there are often HD backhauls to stations at 45 mb and higher. You can split hairs about the numbers but the bottom line is exactly what I said it was, that HD delivered by backhaul to stations often has the potential to knock your socks off compared to what we mere mortals are ever allowed to see. I have seen it myself, and on a number of occasions have had to go retrieve my socks.
Frankly, I'm not sure where backhaul came from, as they are really fronthauls. A backhaul would indicate a reverse feed from the network to the origination site.
As mentioned, the CW delivers their feed to the affiliates using QPSK at 40 Mbps (45 Mbps mux). Many feeds to Canada are QPSK using 45 Mbps mux rates (unfortunately encrypted). Unfortunately, Canada only gets their Warner Bros. and NBC Universal product from the Warner Bros. GDMX service @ 14.5 Mbps, H.264.
I see it everyday with my two dishes. So know how great the video can be.
CBS used a Grammy fronthaul backup of their fiber feed via 8PSK, with the video running 75 Mbps MPEG-2 4:2:2 (peak).