From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Received: from joan.kewl.org ([212.161.35.248]) by www.linuxtv.org with esmtp (Exim 4.63) (envelope-from ) id 1Krf81-0006JH-DU for linux-dvb@linuxtv.org; Sun, 19 Oct 2008 22:43:58 +0200 From: Darron Broad To: Georg Acher In-reply-to: <20081019195409.GW6792@braindead1.acher> References: <412bdbff0810171104ob627994me2876504b43c18d8@mail.gmail.com> <2207.1224273353@kewl.org> <412bdbff0810171306n5f8768a2g48255db266d16aa8@mail.gmail.com> <5905.1224308528@kewl.org> <20081019195409.GW6792@braindead1.acher> Date: Sun, 19 Oct 2008 21:43:53 +0100 Message-ID: <19262.1224449033@kewl.org> Cc: Linux-dvb Subject: Re: [linux-dvb] [RFC] SNR units in tuners List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: linux-dvb-bounces@linuxtv.org Errors-To: linux-dvb-bounces+mchehab=infradead.org@linuxtv.org List-ID: In message <20081019195409.GW6792@braindead1.acher>, Georg Acher wrote: hi >On Sat, Oct 18, 2008 at 06:42:08AM +0100, Darron Broad wrote: > >> The trouble there is that the scaling for the cx24116 already works >> from an end-user perspective. The value derived in the code is >> a possible maximum of 160 from the chip. REELBOX decided on 176 >> which may be more accurate. > >The reelbox code was just a heuristic approach to scale the value so that >less than 30-40% is where the trouble starts... I've more or less matched it >to femon's colors. There was no intention to indicate dBs, as end users >don't understand dBs anyway ;-) All sat receivers I see just scale to fit. We can read lots of forum posts where people exchange % readings for sats :-) >The docs for the 24116 say that the snr is measured in 0.1dB steps. The >absolute range of registers a3:d5 is 0 to 300, so full scale is 30dB. I >doubt we will see the 30dB in a real-world setup... Okay, so we know the step size of 0.1 per bit and that's measured within a range of 0 to 300 but that doesn't actually say what it's value is? Ie, is 50=5dB or something else? All the graphs I see for QPSK and 8PSK in use in the real-world suggest the theoretical limit of esn0 is a lot less than that available range. I don't know what is the accepted error rate to set this limit. Perhaps someone who has authority on this subject can chime in? On the cx24116 testing observed that a register max of 160 from QPSK gave good approximation to that given by regular sat-kit sitting around 100%. If that really means 16dB then it doesn't look right compared to the graphs I see, what's wrong here? >The signal strength in 9e/9d is the value of the AGC voltage. Register da >seems to contain the estimated power level (-25 to -70dBm), but there's no >further information about that (step size etc). I guess the firmware derives >it from the AGC settings. Okay. All that's done in cx24116.c is take that val and invert it, which is enough I suppose. cya! -- // / {:)==={ Darron Broad \\ \ _______________________________________________ linux-dvb mailing list linux-dvb@linuxtv.org http://www.linuxtv.org/cgi-bin/mailman/listinfo/linux-dvb