FEC and SR - Help

[iBoston]

I have a NewTec DVB modulator. I set it up years ago and for the most part it works, but i have noticed some oddities over the years and i wonder if the FEC and SR have anything to do with it.

Currently, i have it set to : DVBS 1/2 FEC SR 30000

The modulator is 99% used with DCII signals and Dish Turbo 8psk signals. Those signals are then output to the above setting. My question is, is there more of a science to this than just picking any SR rate. Is there a way based on what signals im mostly utilizing, what output settings i should be using?

Example : Common dish network signals would be : DVBs FEC 2/3 with an SR 20500 or 21500
Common DCII signal would be : DVBs2 FEC 5/6 SR 30000 or DCII FEC 3/4 SR 29270

Does it matter what i set my Modulator too?? Thanks!

 

[iBoston]

Well, after doing some tinkering :

I found this link : Satbroadcasts.com - no. 1 source for professional work

With my DSR6000 DCII Commercial Receiver, i tuned to a channel. We will call it TurboChannel. I got the DCII tuner to spit out the following information :

RS Locked: No VIT Locked: No BER estimate: 0.000000 Modulation Mode: Turbo 8PSK Symbol Rate: 21.50 Msps Code Rate: 2/3 1.92 Spectral Inversion: Normal FEC Phase: 0 Frequency: 1236.000000 MHz SNR estimate: 18.457031 db Carrier Error: -0.822774 MHz Output Bit Rate: 41.200001 Mbps RS uncorrectable errors: 0 Input Power: -46.913193 db

I noticed the BitRate was 41 Mbps. Using the Calculator in the link above, i piped in my Modulator settings of DVBS FEC 1/2 and SR of 30000, and it calculated at bitrate of 28 Mbps. My bitrate falls short of the original source. That sounds potentially problematic. I reset the modulator to DVBS FEC 7/8 which is the highest i can set on the DVBs modulator. I then re-ran the calculation of the new settings and the website calculated a bitrate of 48 Mbps, which is now above the source bitrate.

So far, the video looks to have no issues. In the past, i noticed little glitches such as flashing on certain services. It might be fully resolved, but ill have to let time and different channel surfing see if the problem is resolved.

I originally picked 1/2 because i split the signal to 5 separate coax cables, and i know the lower the fec, the lower the db required to gain the signal. But, i also see, it limits the total bandwidth, i am assuming as a trade off for forward error correction. I switched it to 7/8 without issues and my signal is 24dB. Very strong.

If anyone has any thoughts, I'm all EARS.

 

[Brct203]

Well, after doing some tinkering :

I found this link : Satbroadcasts.com - no. 1 source for professional work

With my DSR6000 DCII Commercial Receiver, i tuned to a channel. We will call it TurboChannel. I got the DCII tuner to spit out the following information :

RS Locked: No VIT Locked: No BER estimate: 0.000000 Modulation Mode: Turbo 8PSK Symbol Rate: 21.50 Msps Code Rate: 2/3 1.92 Spectral Inversion: Normal FEC Phase: 0 Frequency: 1236.000000 MHz SNR estimate: 18.457031 db Carrier Error: -0.822774 MHz Output Bit Rate: 41.200001 Mbps RS uncorrectable errors: 0 Input Power: -46.913193 db

I noticed the BitRate was 41 Mbps. Using the Calculator in the link above, i piped in my Modulator settings of DVBS FEC 1/2 and SR of 30000, and it calculated at bitrate of 28 Mbps. My bitrate falls short of the original source. That sounds potentially problematic. I reset the modulator to DVBS FEC 7/8 which is the highest i can set on the DVBs modulator. I then re-ran the calculation of the new settings and the website calculated a bitrate of 48 Mbps, which is now above the source bitrate.

So far, the video looks to have no issues. In the past, i noticed little glitches such as flashing on certain services. It might be fully resolved, but ill have to let time and different channel surfing see if the problem is resolved.

I originally picked 1/2 because i split the signal to 5 separate coax cables, and i know the lower the fec, the lower the db required to gain the signal. But, i also see, it limits the total bandwidth, i am assuming as a trade off for forward error correction. I switched it to 7/8 without issues and my signal is 24dB. Very strong.

If anyone has any thoughts, I'm all EARS.

I would expect that to work properly, the modulator should have a throughput at least as high as the signal you're feeding it. But the numbers you are showing above, I would guess they are for the entire mux, not for the one channel you are pushing through (unless of course you are remodulating the whole mux). It's very unlikely a channel would have a 41 Mbps bitrate, even broadcast quality feeds are usually below 15 Mbps.

So I'd say that if you're modulating only one channel, then your choice of SR anbd FEC is probably more than enough