Dish size for DVB-S2?

[navagator]

Hello,

Just curious, will the new RTN DVB-S2 signals require a larger dish? I'm mainly concerned with G10 as I have a fairly large dish for C band reception.

I'm currently using a Primestar dish for G10, great little dish.

Will I need to upgrade to a larger KU dish or maybe go with a Corotor on the big dish?

Thanks

Doug

 

[Lak7]

I get RTN DVB-S2 on G26 with 10' and BSC621 C Band. Q in the 80's. I have not seen/read about any RTN Ku DVB-S2 yet. Maybe somebody here knows.....

 

[Mr Tony]

honestly we don't know

I do know that people have received the G26 stuff with a 7 1/2 foot dish. I am yet to lock it with my 6 footer but IA6 seems to give me fits. I think its a combination of the smaller dish and it being my true south. When I blind scan, I get a couple things on IA6, a couple strong feeds (although they show up weak) from G3 and once in a while a weak feed that is from G11

I am able to max out the meter on the KU DVB-S2 mux on AMC2 with the 30" dish (sure they're data TP's but they are good for aiming)

 

[navagator]

Thanks for the info, I Guess time will tell.

Personally I hope the DBV to DVB-S2 conversion is a slow process. I just bought my Visionsat 6 months ago and I would like to get at least a few more months use out of it. It's a great receiver.

I am looking forward to receiving the new RTN feeds on G26 though.

Doug

 

[stogie5150]

I can get the DVB-S2 Cband feeds on G26 with a 7.5 dish with great SQ.

But, I am going to say this, if you have a choice, ALWAYS, ALWAYS, ALWAYS,ALWAYS,ALWAYS

Go with the bigger dish for Ku, Dvb-S2 or not. :up

 

[navagator]

I'd like to add a Corotor to the big dish someday. But to be honest I'm not completely sure our big dish will work for KU, I hope it will.
We have an older 12 foot Conifer mesh dish with larger sized holes. The mesh is made up of elongated hexagonal holes rather than the smaller round holes. I did check to see if a number 2 pencil would fit through one of the holes and fortunately it didn't, so hopefully it will work.

 

[jself1982]

I have read several places that certain networks request/require a 12'-14' dish for the FEC of 7/8 for DVBs2. I myself have a 10 footer but I don't have DVBS2 capabilities yet. Just remember, the higher the FEC, the larger the dish you need [or the best tuned dish].

 

[truckracer]

7/8 fec doe not leave much for error correction. The signal has to pure. I hope a 10' well tuned will take care of most s-2 feeds when I get something to receive them.

 

[Mr Tony]

From what I've heard and read we shouldn't have issues with the dish size when some channels on KU goes DVB-S2. Our existing dishes will be fine

 

[glen4cindy]

From what I've heard and read we shouldn't have issues with the dish size when some channels on KU goes DVB-S2. Our existing dishes will be fine

Which dishes are you referring to here, C or Ku?

Also, what do the different values for FEC actually mean? I've seen 1/2, 3/4, 2/3 among others. I know they have said here that 7/8 means there is not much margin for poor signal. Why?

Thanks for educating a newbie here.

 

[brentb636]

An FEC of 1/2 means that 1 bit of every two bits sent is used for error correction purposes. That's a very high error correction ratio and pretty much guarantees that an stb can reconstruct a messed up signal. An FEC of 7/8, however, has only 1 bit of error correction for every 7 bits of data. In such a case, a poor signal would not have much chance of being corrected using the error correction algorithm's .
There's a class for Sat truck techs , on 97W , most every day, 11779 H 3979-3/4 , which covers FEC and many other related subjects for establishing a good "shot" . It's interesting to see the effect as the operator changes the FEC on the same datastream. I love hardware !!
It's a good class, I've watched it several times, once the instructor was a good looking gal. Maybe you'll get lucky !

Brent

 

[Mr Tony]

Which dishes are you referring to here, C or Ku?

KU

Also, what do the different values for FEC actually mean? I've seen 1/2, 3/4, 2/3 among others. I know they have said here that 7/8 means there is not much margin for poor signal. Why?

Thanks for educating a newbie here.

brent pretty much summed it up. A FEC of 7/8 means you need either a bigger dish or a well fine tuned signal. The Equity mux on G3 C-Band is 7/8 and even at a 60 quality I can have issues (pixeling, freezing). I need the quality to be above 68 or so

Conversely on G10 the mux is 3/4 and can kleep it stable at a 30 quality

 

[Stefan]

But keep in mind it's not just about FEC rate. Modulation is a factor as well and for a given FEC rate 8psk is harder to lock than Qpsk. It's true that 8psk dvb-s2 is easier to lock than 8psk dvb-dsng but it's still requires a higher signal to noise ratio than qpsk dvb-s. Based on the information I've looked at an dvb-s2 8psk signal with an FEC rate of 3/4 requires just a tad bit higher signal to noise ratio that a qpsk dvb-s signal with an FEC rate of 7/8. So, if you have trouble with the dvb-s qpsk c-band mux on G3c that has an FEC rate of 7/8 your gonna have a bit more trouble with the 8psk dvb-s2 mux that's 3/4 on G26. Don't believe me? Take a look at the chart on page 11 of this document.

http://orderedwords.net/badgers/tandberg/Tandberg DVBS-2 guide.pdf

You'll see that there's a recommended minimum of 7.91 db for 3/4 8psk dvb-s2 versus 7.24 db for 7/8 qpsk dvb-s. So, the answer to this thread is it could indeed require a bigger dish depending on what FEC rate they're gonna use.

 

[chapelrun]

Interesting Article

I read most of this article. (not understanding alot of it).

Does anyone know what most DVB-S2 TV broadcasters plan to use or are using in terms of mode? (QPSK or 8PSK)

Page 17 talked about Backward Compatible Broadcast Mode which I thought was interesting. I wonder if Equity and others are using or plan to use this as folks upgrade their receivers.

Much information in the article went over my head but I still thought it was a good read if you are interested in how DVB-S2 works.

 

[Mr Tony]

Equity will be using DVB-S2 8PSK

 

[tifozi]

But keep in mind it's not just about FEC rate. Modulation is a factor as well and for a given FEC rate 8psk is harder to lock than Qpsk. It's true that 8psk dvb-s2 is easier to lock than 8psk dvb-dsng but it's still requires a higher signal to noise ratio than qpsk dvb-s. Based on the information I've looked at an dvb-s2 8psk signal with an FEC rate of 3/4 requires just a tad bit higher signal to noise ratio that a qpsk dvb-s signal with an FEC rate of 7/8. So, if you have trouble with the dvb-s qpsk c-band mux on G3c that has an FEC rate of 7/8 your gonna have a bit more trouble with the 8psk dvb-s2 mux that's 3/4 on G26. Don't believe me? Take a look at the chart on page 11 of this document.

http://orderedwords.net/badgers/tandberg/Tandberg%20DVBS-2%20guide.pdf

You'll see that there's a recommended minimum of 7.91 db for 3/4 8psk dvb-s2 versus 7.24 db for 7/8 qpsk dvb-s. So, the answer to this thread is it could indeed require a bigger dish depending on what FEC rate they're gonna use.

Interesting, thanks for the info. Probably why i can never lock Tp 15 on AMC1 (12000H/28755 FEC 2/3 -> DVB-S 8PSK) on my Merc II.

 

[brentb636]

Merc II is strictly Qpsk , can't get 8psk, sad to say. Thanks to your post, though, I may try it with my skywalker-1 , it shouldn't have a problem with 8psk.


Brent

 

[tifozi]

Merc II is strictly Qpsk , can't get 8psk, sad to say. Thanks to your post, though, I may try it with my skywalker-1 , it shouldn't have a problem with 8psk.


Brent

Good catch i forgot to RTM Please let us know if the Skywalker locks it ..i have an exactly similar setup as you ... have the Skywalker slaved to the Merc II ... it probably doesn't work in the slave mode ? If connected directly to the RG6, i think it will definitely work.

 

[qwert1515]

It should work in slave mode, as long as the master receiver is on the same polarity. The master receiver passes the IF band 950 - 2150 MHz un-changed to the next receiver.

 

[brentb636]

Good catch i forgot to RTM Please let us know if the Skywalker locks it ..i have an exactly similar setup as you ... have the Skywalker slaved to the Merc II ... it probably doesn't work in the slave mode ? If connected directly to the RG6, i think it will definitely work.

I don't have a hint of a lock with the skywalker-1 and Tsreader. Since the channel was reported in '05, I suppose it may not even be there currently. Nice to know, though, so we could practice on it. [edit] I've used the skywalker both slaved to the Merc, and simply directly connected to the other output of the Invacom lnbf. Both ways work fine, but the direct connect is more convenient since I simply aim with the Merc, and the skywalker has the whole bird.



Brent