[linux-dvb] TDA10086 fails? DiSEqC bad? TT S-1401 Horizontal transponder fails

Oliver Endriss o.endriss at gmx.de
Thu Apr 10 22:40:13 CEST 2008


Hi,

Manu Abraham wrote:
> Oliver Endriss wrote:
> ...
> > Ok, some calculations according your formula
> > 
> >>>>> BW = (1 + RO) * SR/2 + 5) * 1.3
> > 
> > 45 MSPS:
> > BW = ((1 + 0.35) * 45/2 + 5) * 1.3 = 46
> > 
> > -> cutoff 36 MHz (maximum value supported)
> > 
> > 27 MSPS:
> > BW = ((1 + 0.35) * 27/2 + 5) * 1.3 = 30,2
> > 
> > -> cutoff 31 MHz
> > 
> > 22 MSPS:
> > BW = ((1 + 0.35) * 22/2 + 5) * 1.3 = 25,8
> > 
> > -> cutoff 26 MHz
> > 
> > Are these calculations correct, or did I miss something here?
> 
> 
> It looks fine, just round it off to the next integer. ie always round it
> up, rather than rounding it down. For the cutoff at 36MHz, it is fine as
> well, since at the last step, you will not need an offset, since it
> would be the last step in the spectrum.
> ...
> > Afaics a simple pre-calculated lookup table with 32 entries should do
> > the job. At least for the cut-off frequency.
> 
> That's possible, since you need only 32 precomputed entries, rather than
> continuous values. That would be much better too, without any runtime
> overheads. Just the table needs to be done nice.

Now I found some time to come back to this issue,

I prepared a small patch to set the cutoff according to Manu's formula.
The calculation is simple enough for integer arithmetic, so it is not
worth to prepare a lookup-table.

@ldvb:
Please test and report whether it works for you.

CU
Oliver

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