Hi Oliver, Oliver Endriss wrote: > Hi, > > Manu Abraham wrote: >> Hi Hartmut, >> >> Hartmut Hackmann wrote: >> >>> This might be right! I could not get good information regarding the >>> transponder bandwidths. We might need to make this depend on the >>> symbol rate or a module parameter. >> You can calculate the tuner bandwidth from the transponder symbol rate >> (in Mbaud) for DVB-S: >> >> BW = (1 + RO) * SR/2 + 5) * 1.3 > > Apparently I need some lessons in signal theory. ;-) > What does R0 stand for? RO stands for Rolloff. This isn't anything big, but just defines the sharpness of the bandwidth curve. You can think how a filter's bandwidth would look like, when it is plotted out. This is just a filter characteristic. Normally why you need this is not new. Traditionally for old PLL based tuners, this used to be in hardware, ie a LC component in the pre stages, prior to the tuner. With the arrival of Silicon Tuners, things do have changed. These things have been made software configurable. There are advantages and disadvantages to this. Well, there's so much that can talked about it, but well let me not make it too long. For Broadcast applications, ie all TV signals that we receive RO = 35% We do have other rolloff as well, but generally the others are not used in broadcast apps, but for professional purposes. When you have a lower rolloff, what happens is that the filter is more of a tuned filter and considered narrower slightly. The advantage of a narrower filter is that since the edges fall of sharply, lesser power is wasted, but brings in the disadvantage that the spectrum is a bit more congested, but alternatibvely somebody could just argue as well, you can pack in more into the entire spectrum. > Do we have to select a higher cut-off value to compensate for the LNB > drift and other stuff like that? The "5" in there, is in fact implies +/-5Mhz for the LNB drift (5 Mhz on either side off the offset. A LNB can drift in either direction at different periods of the day, depending on the temperature. This drift can cause an acquisition to fail, or an already acquired LOCK to fail on a very general note). The drift is standard and is specified in one of the ETSI specifications, one which i read a while back but don't remember the specification number. Regards, Manu _______________________________________________ linux-dvb mailing list linux-dvb@xxxxxxxxxxx http://www.linuxtv.org/cgi-bin/mailman/listinfo/linux-dvb
