Johannes, Thank you very much for your information. I don't know if your answer is very satisfying for my needs, but at least, that is very clear !
I've just read on this mailing-list archives (Apr-2002) that the SNR results should be divided by 1.000.000 (1E-6) in order to be read in dB (?). One of my collegues did an experimentation between a field measurer (MCP3000) and the SNR value on the card output... and I noticed that the comparison between both results are <<<APPROXIMATIVELY>>> "1.000.000"... I will wait for Holger's comments, if he has some more info or patches. Thanks again Samuel > -----Original Message----- > From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] > On Behalf Of Johannes Stezenbach > Sent: lundi 2 juin 2003 13:21 > To: Samuel Torton > Cc: [EMAIL PROTECTED] > Subject: [linux-dvb] Re: Needs to get the SNR value in dB, with dvbtune > > Samuel Torton wrote: > > > > In order to get the SNR value, I used the following lines in the > > "tune.c" source code: > > ------------------------------------------ > > strength=0; > > ioctl(fd_frontend,FE_READ_SNR,&strength); > > fprintf(stderr,"SNR: %d\n",strength); > > ------------------------------------------ > > > > My questions are : > > - What's the unit of the value FE_READ_SNR to be displayed ? > > Usually, a big number is displayed, but I want to display this value > > in dB, so is there any math formulae to apply, in order to get > > this value in dB ? > > If yes, what is it ? (*) > > - Same questions for FE_READ_BER, FE_READ_SIGNAL_STRENGTH > > The values SNR and signal strength are whatever the frontend hardware > gives us, possibly stretched into a range of 0..0xffff. > For the BER, I don't even know... > > > (*) For example, if I install this DVB card on a Windows box, with > > WinTV software tools on Windows, I can see the SNR level in a color bar, > > and the value expressed in dB, such as in the example provided in this > > image: http://www.hauppauge.fr/sup/cap/nexus2.jpg > > We don't know how to convert the values from the hardware into dB, > because a) we don't have enough information about the hardware, > b) we don't have time to do it by experimentation. > > Patches are probably welcome, check with Holger. > > I also doubt that the values that WinTV displays are calibrated, they > might be off by some considerable amount. After all the DVB cards are > not made for signal measurements. > > > Johannes > > > -- > Info: > To unsubscribe send a mail to [EMAIL PROTECTED] with "unsubscribe linux- > dvb" as subject. -- Info: To unsubscribe send a mail to [EMAIL PROTECTED] with "unsubscribe linux-dvb" as subject.
