Hi, Klaus Schmidinger wrote: > Dave Chapman wrote: > >>On Tuesday 08 October 2002 22:19, Klaus Schmidinger wrote: >> >>>Are these frequency offsets always +/-167kHz? Will that be the same for >>>other countries, too? >> >>In the UK the offsets (if present) are always +/- 167KHz. I haven't heard >>about offsets being used in other countries.
Only +/-166667 offsets are specified in the DVB standard. >>>I'm asking because I would like to make the frequency for DVB-T channels >>>in VDR's channels.conf also be in MHz, and if that offset thing is in any >>>way standardized we could just add another DVB-T specific parameter to >>>cover the offset (like O0 = 0 kHz, O1 = +167 kHz, O2 = -167kHz). >>> >>>I wonder, though, why that offset is necessary, and whether the driver >>>shouldn't be able to tune to a channel at, say, 490 MHz - 167 kHz >>>automatically if it is given an inital frequency of 490 MHz. I mean >>>167 kHz isn't _that_ far off for a transponder with several MHz bandwith. >>>Or am I missing something important here? >> >>No, trying to tune to a frequency of 488.833MHz by approximating to 489MHz >>doesn't work - I've just tried it. > > > That's odd... IIRC with DVB-S you can be off by even 1 or 2 MHz and the driver will > tune to the transponder correctly, so I really wonder why this isn't possible with > DVB-T. I mean it's just a mere 166 kHz! Is there no AFC in the DVB-T part of > the driver? > > Can one of the driver developers comment on this? That was probably the zigzag scan. It's range is 1000 times wider for DVB-S since frequencies are there measured in kHz, not Hz to prevent an overflow. For DVB-C/T we need a finer stepsize since the frequencies there are much smaller. If you want to achieve fastest possible tuning you should pass the exact frequency. All demodulators have built-in AFC's too, but their range is sometimes pretty limited - and even there you can speed up tuning when you pass the exact frequency. >>I think the "O" option would just make the channels.conf more confusing - it >>is much simpler just to keep the frequency the way it is, in KHz. > > > The problem is that I would like to be able to use the transponder frequency > as a parameter in a "unique channel ID" (I know, there are people who would > like that to be the NID, TID whatsoever - there will be a switch to configure that!). > Anyway, since the "official" frequencies are apparently given as integer MHz values > (for instance 23 * 8 + 306) and the "offset" is mentioned as an additional parameter, > see >http://www.itc.org.uk/uk_television_sector/reception_advice/digital_trans_guide/show_transmitter.asp?siteID=81. > So I would prefer _all_ frequencies in channels.conf to be in MHz, so that the >numbers > can be expressed in 16 bit values. And regarding channels.conf being "confusing": >well, > that's mainly because DVB-T needs so many parameters! I don't know why they have to > have _that_ many of them, but that's just the way it is. And apparently the "offset" > is just another of these parameters. Why don't you want to use 32-bit frequencies? > Can somebody with DVB-T please run a program that parses the NITs and reports > the transponder frequencies given there? I'd say if these are given as the "real" > values (like 488.833MHz), then VDR should store them as such in channels.conf. > But if they are given as integer MHz values (like 489MHz) then there's no point in > having them in kHz in channels.conf. The NIT's report frequencies in 10Hz steps for DVB-T, in 100Hz steps for DVB-C and in 10kHz steps for DVB-S. Holger -- Info: To unsubscribe send a mail to [EMAIL PROTECTED] with "unsubscribe linux-dvb" as subject.
