[linux-dvb] dvb-s2 parameters - rolloff & pilot

Manu Abraham abraham.manu at gmail.com
Fri Dec 14 22:47:50 CET 2007


Georg Acher wrote:
> On Fri, Dec 14, 2007 at 08:28:12PM +0100, Andreas Oberritter wrote:
>  
>>> dvb-s2 rolloff
>>> 0=0.20 (DVB-S2)
>>> 1=0.25 (DVB-S2)
>>> 2=0.35 (DVB-S2/DVB-S)
>> You can get the roll-off factor from the satellite delivery system
>> descriptor, which is specified in ETSI EN 300 468 V1.8.1 (2007-10). The
>> syntax of this descriptor was changed with the introduction of DVB-S2.
> 
> At least on the CX24416, I've found no significant differences when changing
> the rolloff-value. It may have bigger effects on weak or more adjacent
> signals, but I don't think a false setting will have an impact on locking.
> 

The normative rolloff for Broadcast Applications is 35%. When you have a filter 
characteristic with a lower slope, it would be insignificant for the filter to be set 
up with characteristics of a larger slope, thereby implying no difference in any 
sort of performance or in any manner.

But in any case the larger slopes, 25% and 20% are used in either professional 
applications or in DSNG slots. In the case of the CX24116 only the DSNG slots do
matter, since the CX24116 doesn't support 16APSK and higher up which are 
used for professional applications and interactive services.

Also, we do not have any DSNG eqpt. for the home users except for some of the 
remote access terminal vendors, but they also do not depend on the QPSK/8PSK
feature alone.

But that said, when you are trying to lock to a DSNG slot eg: rolloff=25%, if you 
specify a filter characteristic of 35% and there you go ... LOCK will surely FAIL most 
cases, although if you are lucky enough you might get a LOCK, like winning a lottery.

Regards,
Manu



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