An odd quality "thing"

[RT-Cat]

An odd thing about quality and holding a picture.
MeTv -101 clean dish-no snow: S-90 Q72 perfect picture. Fill the dish up with snow and Q drops to 45 and picture goes out or freezes.
Now go to 103 Ion East HD on 4040, NO SNOW on dish. S-90 Q-4, 25, 30, 14, 4, 7, 9 bouncing all over the place. BUT perfect picture! No break up, no problem.
So how is it possible to have Q at 45 and no picture, but have another channel as low as Q of 4 and not have ANY breakup. What is so good about Ion on 4040?

 

[Mr Tony]

The FEC is different (Forward Error Correction)

MeTV (according to Lyngsat) is 5/6
Ion is 2/3
(3/4 is what alot of stations use)

Here is some technical info on it
http://en.wikipedia.org/wiki/Forward_error_correction
http://excellentthreads.blogspot.com/2011/10/what-is-forward-error-correction-in.html

In "simple terms" the higher the FEC the more signal you need to keep it stable. 1/2 is the lowest and back in the day White Springs used that. You could literally have 0 quality and it would be stable. Thats also why when I had my 6 foot dish I could get most everything but the CBS HD feeds because they were 9/10.

Back when Equity had their KU feeds and the C-Band the KU was 3/4 FEC but the C-Band was 7/8. So on my old Pansat 1500 a 30 quality would keep the KU stable but needed a 75 or greater to keep the C-Band stable.

 

[catamount]

Iceberg nailed it. Back when I was mini-bud testing , I could get Word network on 91 West showing 0 Quality on the viewsat. The CNX showed 5 Quality. Other transponders needed either 26 or 37 to remain stable.

Catamount

 

[Mr Tony]

I remember I could get Florida Channel on 87W with 2 or 3 quality....its 2/3 FEC too

 

[Mr Tony]

Iceberg nailed it. Back when I was mini-bud testing , I could get Word network on 91 West showing 0 Quality on the viewsat. The CNX showed 5 Quality. Other transponders needed either 26 or 37 to remain stable.

Catamount

looking at Lyngsat Word Network is a 1/2 FEC

 

[RT-Cat]

Great pile of information. Answered my question very well. One part of the info brought back memories of the early days of when I first messed with FTA: "In some early digital receivers, the FEC parameter has to be typed in by users. As the process rate of the CPU of digital receivers improves, today's digital satellite receiver can measure the FEC parameter automatically, thus users don't have to type in the parameter any more." My first receiver had to be typed in.

 

[. Raine]

Why don't they all use the better FEC? Is it that the equipment for better is more expensive?

 

[Mr Tony]

Why don't they all use the better FEC? Is it that the equipment for better is more expensive?

define better? Higher (as in 9/10) or lower (as in 1/2)?

the lower the FEC (1/2 being the lowest) the easier it is to pick up on a "smaller" dish...there is plenty of room for error correction to keep the signal stable.

There is no difference if you run 1/2 or 7/8. Again it all depends on how much of the signal you are going to use to "clean up the crap" and have it play smoothly. For us hobbyists we want lower (1/2, 3/4). Once you get to 5/6 then you start needing preciser aiming or a bigger dish

 

[waylew]

Why don't they all use the better FEC? Is it that the equipment for better is more expensive?

Simple answer,and I think I got it more or less right,FEC 9/10,90 percent of the signal is used for picture info,FEC 1/2,half of the signal is used for picture info.

 

[Mr Tony]

Simple answer,and I think I got it more or less right,FEC 9/10,90 percent of the signal is used for picture info,FEC 1/2,half of the signal is used for picture info.

thats how I understand it

 

[. Raine]

I was thinking better as lower, in being easier to receive. If the signal is going to be broadcast, then why not use the lower FEC and make it more reliable, is what I was thinking. I think from Waylew's post that probably in say, 1/2 FEC, half of the signal is used for picture info and then the other half is used for whatever else, guide, captioning, etc?

Or is it half of the signal is for picture info and the rest is for FEC, thus less FEC would equal better picture quality, but tougher to receive?

 

[northgeorgia]

I was thinking better as lower, in being easier to receive. If the signal is going to be broadcast, then why not use the lower FEC and make it more reliable, is what I was thinking.

I may be wrong here but I think, at least as far as this goes, when you start looking at the broadcasts at 9/10 FECs and many of the 7/8 FECs, they're mostly feeds for networks with huge dishes set on the satellite to rebroadcast, and not intended for the FTA viewer.

 

[waylew]

I was thinking better as lower, in being easier to receive. If the signal is going to be broadcast, then why not use the lower FEC and make it more reliable, is what I was thinking. I think from Waylew's post that probably in say, 1/2 FEC, half of the signal is used for picture info and then the other half is used for whatever else, guide, captioning, etc?

For those to whom these signals are intended,they have the equipment to reliably receive said signals,big dishes etc.And they want the best quality to start with,before they downgrade,compress,and sub channel it to death.As far as CC,etc,that stuff uses a very small (insignificant) part of the signal.Being easier to receive is mainly a concern for us,and being as we're not the intended target,we are of no concern at all to them,with a few exceptions.

 

[. Raine]

Northgeorgia and Waylew, thanks for explaining that, I got it now! Wasn't thinking along the lines of that FTA'ers aren't the intended recipients of the signal. Makes perfect sense to me now, thanks.

 

[N0QBH]

I was thinking better as lower, in being easier to receive. If the signal is going to be broadcast, then why not use the lower FEC and make it more reliable, is what I was thinking. I think from Waylew's post that probably in say, 1/2 FEC, half of the signal is used for picture info and then the other half is used for whatever else, guide, captioning, etc?

Or is it half of the signal is for picture info and the rest is for FEC, thus less FEC would equal better picture quality, but tougher to receive?

Been coding for another project that uses FEC and have had to learn a little about it. The fraction or ratio is the the number of bits in over the number of bits out of the FEC encoder. The larger the difference, the more error correction capacity. The smaller the difference, the more efficient it is.

 

[stanleyjohn]

So in simple terms! The higher the fraction the better the picture quality.

 

[Balock]

Not directly: The higher the FEC value (7/8 vs 1/2, for instance) the less information the receiver now has to correct errors encountered in the received data, therefore the ability to maintain the original quality of the picture is reduced and the better the signal required to receive. The broadcaster could still send a crappy original no matter the FEC used

EDIT: Corrected my original statement

 

[Titanium]

Audio, CC, EPG data is allocated as part of the transport stream and don't use the "extra" space afforded by lower FEC. Picture quality is only one factor when a satellite broadcaster selects a FEC. A link budget determining the delivery requirements of a service is created while arranging for the lease or usage of bandwidth on a satellite. Together, the signal type, power, FEC and bandwidth selection determines the robustness and quality of the service. This calculation determines the parameters required to deliver the complete transport stream (that encapsulates the video, audio, cc, epg, etc.) within a specific region using minimium equipment requirements with an expected up-time.

If the link budget is for the downlink facilities which have small aperture dishes, located near the edge of a footprint or where conditions affect reception, then a lower FEC might be selected. This lower FEC is not as efficient by using the least amount of bandwidth to deliver the same data, but it would allow smaller dishes or in regions with inclement weather conditions to receive enough data and have more data duplication to mask the errors that are caused from not receiving all of the data on the first pass.

Downlinks with larger dishes, located in prime footprints and minimal signal attenuation receive more data without errors and do not require the extra duplication of data to mask and correct errors. For these link budgets, a higher FEC might be used so either less bandwidth is used (lower cost) or the same bandwidth is used to provide increased picture, audio or data streams.

 

[toucan-man]

...For these link budgets, a higher FEC might be used so either less bandwidth is used (lower cost) or the same bandwidth is used to provide increased picture, audio or data streams.

CBS.

 

[Mr Tony]

I may be wrong here but I think, at least as far as this goes, when you start looking at the broadcasts at 9/10 FECs and many of the 7/8 FECs, they're mostly feeds for networks with huge dishes set on the satellite to rebroadcast, and not intended for the FTA viewer.

yup pretty much