PacersGuy said:
Mike,
Just curious - how does one find out what bandwidth a transmission is in?
steve
Well you can see what the transponder capacity is:
1. Go to
www.lyngsat.com
2. pick packages->america
3. pick a satellite (like 110 for dish HD) then click on "freq"
This will give you a list of what channels are on which transponder.
For example HDNet/Movies are both on transponder 7
Using the codes you will see the symbol rate (SR) is 21500, the error correction (FEC) is 2/3. Dish broadcasts HD in 8PSK and uses the standard R/S error correction at 188/204. So you have to plug into the formula:
symbol rate * bits in a symbol * FEC * R/S is the transponder bit rate:
8PSK is 3 bits in a symbol so:
21500 * 3 * 2/3 * 188/204 = 39.6 mbit/sec (this is what dish uses on all their HD TPs at this time)
So, 39.6 is the data rate. There is some overhead on the transponder for everything to the info button to packet overhead. Even if you "give" a megabit/sec to that (I think it is much less) and still have more than the 38.4 data rate needed divided up by the two channels to give 19.2 mbit/sec each.
3/TP on dish would be around 13 Mbit/sec if they all peaked at the same time. But, the three channels share the bandwidth dynamically, so it is better than it looks since a channel can hit 19.2 while the other ones are not so busy. You are playing the odds.
DIRECTV is doing 20000 * 2 * 6/7 * 188/204 = 31.6 on a TP. DIRECTV used to only have 1 HD and some SD on a TP giving the HD the full 19.2. Now it is reported that they put 2 or 3 on a TP giving an average of 15.8 (2/TP) or 10.53 (3/TP).