Em Sat, 02 Nov 2013 23:31:58 +0200
CrazyCat <crazycat69@xxxxxxxx> escreveu:
> Mauro Carvalho Chehab пишет:
> > This is wrong, as it breaks for 6MHz-spaced channels, like what's used
> > in Brazil and Japan.
> >
> > What happens here is that, if the tuner uses a too wide lowpass filter,
> > the interference will be higher at the demod, and it may not be able
> > to decode.
> >
> > As the bandwidth is already estimated by the DVB frontend core, the
> > tuners should be adjusted to get the closest filter for a given
> > bandwidth.
> >
> > So, the driver is correct (and it is tested under 6MHz spaced channels).
>
> But usual applications only set cable standard (Annex A/C or B) and not set bandwidth. So for annex A/C default selected 6MHz ?
Usual applications set the symbol rate, and symbol rate is easily
converted into bandwidth. The DVB core does that. see
dtv_set_frontend():
switch (c->delivery_system) {
case SYS_ATSC:
case SYS_DVBC_ANNEX_B:
c->bandwidth_hz = 6000000;
break;
case SYS_DVBC_ANNEX_A:
rolloff = 115;
break;
case SYS_DVBC_ANNEX_C:
rolloff = 113;
break;
default:
break;
}
if (rolloff)
c->bandwidth_hz = (c->symbol_rate * rolloff) / 100;
--
Cheers,
Mauro
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