[mythtv-users] Strong signal, ugly artifacts...

Andrea Giuliano sarkiaponius at alice.it
Sun Jun 14 20:33:16 UTC 2009


Well, I checked cables and dish, nothing changed.

One thing I should have mentioned before is that I have an in-line
amplifier that should give a gain of 20 dB, but MythTV always reports
4.8 dB despite the amplifier is present or not. In the latter case,
MythTV reports a signal strength less than 10%.

If MythTV is not fooling me, the amplifier is gone: 4.8 dB is less than
the gain it should give!

On the other hand, the signal strength is dramatically affected by the
amplifier.

I really can't figure this out.

Many thanks anyway to everybody for your kind help.


On Thu, 2009-06-04 at 18:18 -0400, William wrote:
> On 06/04/2009 05:59 PM, Robert McNamara wrote: 
> > 
> > 
> > On Thu, Jun 4, 2009 at 2:53 PM, Andrea Giuliano
> > <sarkiaponius at alice.it> wrote:
> >         
> >         Robert McNamara wrote:
> >                 
> >                 
> >                 On Thu, Jun 4, 2009 at 1:51 PM, Andrea Giuliano
> >                 <sarkiaponius at alice.it
> >                 <mailto:sarkiaponius at alice.it>> wrote:
> >                 
> >                    I'm seeing horrible artifacts in my DVB-S
> >                 recordings, even though
> >                    MythTV says the signal strength is 99%
> >                 
> >                 
> >                 Signal strength isn't what you think it is.  Signal
> >                 strength is the strength of the electrical signal
> >                 between the card and the LNB, *not* an indication of
> >                 quality of the signal.  More helpful for this is SNR
> >                 (Signal to Noise Ratio) and Bit Error.  Low SNR or
> >                 high bit error means bad quality signal.  Repoint
> >                 the dish.
> >                 
> >                 
> >         
> >         
> >         Dear Robert,
> >         
> >         thanks for your kind answer. Can you please give me
> >         reference values for SNR and Bit Error? I got 4.8 dB and
> >         2000-3000 for them, depending on the channels. Actually, SNR
> >         seems to be constant, I mean it's alway 4.8 dB, while BE
> >         changes instead.
> >         
> >         Also, my dish works perfectly fine with my stand alone
> >         decoder (I have two cables from one dish), so I guess it's
> >         not its fault.
> >         
> >         Best regards.
> > 
> > 
> > (Fixed top posting) 
> > 
> > 
> > Hi Andrea,
> > 
> > 
> > Ideally, the BER should be 0 or extremely close to 0.  Different
> > tuner devices have different signal sensitivities and different
> > decoders are more or less sensitive to errors in the stream.  Both
> > are likely problems for you.  You will almost definitely need to
> > point your dish more accurately.  You can also check all your cable
> > termination, the cables themselves, and any power inserters for the
> > LNB.
> > 
> > 
> > Robert
> > 
> 
> The issue is your 4.8 dB SNR. This is very weak and means your signal
> is very noisy. A good reading will be 10dB or more. You should be
> seeing a low BER starting at around 6dB however bad weather will cause
> you to have signal drop outs. You need to check antenna pointing, all
> the cables (water getting into the cable will ruin it even if it looks
> great so if you have any outside cable connections that are not
> waterproofed (covered with a boot or wrapped/painted with coax
> sealant) I would redo those connections and check signal strength
> again.
> 
> W.
> _______________________________________________
> mythtv-users mailing list
> mythtv-users at mythtv.org
> http://mythtv.org/cgi-bin/mailman/listinfo/mythtv-users


More information about the mythtv-users mailing list