[linux-dvb] automated w_scan, duplicated channels and signal strength filtering

Jelle de Jong jelledejong at powercraft.nl
Sat Nov 1 19:41:20 CET 2008

wk wrote:
> Hello Jelle,
>> When a scan is completed it list all found channels, in the file, (see
>> attachment) however this also include duplicated channels with other
>> frequencies and strange channels that are from local unusable broadcast.
> That's most probably what your provider sends inside NIT (network 
> information table).
> w_scan reads it's informations from there. Sometimes these informations 
> are wrong.
>> The issue here is that signal strength is not used to filter out
>> duplicated channels, only the best strongest signal should come in the
>> channel list, and channels without identifiers should be removed.
>> How can we do this? Is somebody able to fix these issues?
> It's not possible to use signal information since nearly every dvb cards 
> sends other information for signal strength,
> please read the discussion regarding SNR/strength some days ago here on 
> the list. From application point of view
> the signal strength information doesn't contain any useful data as long 
> it's not standardized and reliable across all frontends.
> Therefore i decided not to use signal strength. Otherwise some frontends 
> would not work.
> Signals without identifiers will not be removed, since some of them have 
> their channel names inside EIT information or
> inside private data (i.e. Prmiere) and deleting these channels would 
> make other users really unhappy. ;)
> Most of these channels are encrypted, so try to avoid them with -E 0 .
> But channels without video *and* audio will be removed instead.
>> [1] http://wirbel.htpc-forum.de/w_scan/index2.html
>> ps. I can't find any contact info for the developer of w_scan.
> email contact is included in the header of each source file. 
> Nevertheless, should be inside README too, you're right.
> Regards,
> Winfried

Thank you Winfried for both creating the program and to response and
clear op my questions.

I followed the SNR/strength messages and read the thread again, I was
hopping some drivers where already using some system that could be used,
like polling the capabilities of the frontends. I would also suggest
some way of translating the dB to a min(0)(red) and max(100)(green)
value so a decimal number can also be used for representation.

I was also hopping w_scan was going into debian sid repositories, I
would like this for my users, maybe I can find some time next year to
fix this.

Sadly it seems my usability issues can not be fixed in an easy way, lets
hope SNR support and some logic using it during channel scanning will be
coming soon :-p. I can donate 40 euro, dutch stroopwafels, or  some
plushy tux mascots for some extra motivation.

Thanks in advance,


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