Hi, On Tue, Aug 14, 2012 at 2:23 PM, Reinhard Nissl <rnissl@xxxxxx> wrote: > Hi, > > it seems that my 9 years old LNBs got some drift over time, as tuning takes > quite a while until I get a lock. So I thought I could compensate this > offset by adjusting VDR's diseqc.conf. > > Therefore I first hacked some logging into VDR's tuner code to read and > output the above mentioned property once it got a lock after tuning. As > VDR's EPG scanner travels over all transponders when idle, I get offset > values for all transponders and can then try to find some average offset to > put into diseqc.conf. > > So here are several "travel" results for a single transponder ordered by > Delta: > > Sat. Pol. Band Freq (MHz) Set Freq (MHz) Get Delta (MHz) > S13,0E H H 11938 11930,528 -7,472 > S13,0E H H 11938 11936,294 -1,706 > S13,0E H H 11938 11938,917 0,917 > S13,0E H H 11938 11939,158 1,158 > S13,0E H H 11938 11939,906 1,906 > S13,0E H H 11938 11939,965 1,965 > S13,0E H H 11938 11940,029 2,029 > S13,0E H H 11938 11940,032 2,032 > S13,0E H H 11938 11940,103 2,103 > S13,0E H H 11938 11940,112 2,112 > S13,0E H H 11938 11940,167 2,167 > S13,0E H H 11938 11941,736 3,736 > S13,0E H H 11938 11941,736 3,736 > S13,0E H H 11938 11941,736 3,736 > S13,0E H H 11938 11942,412 4,412 > S13,0E H H 11938 11943,604 5,604 > S13,0E H H 11938 11943,604 5,604 > S13,0E H H 11938 11943,604 5,604 > S13,0E H H 11938 11945,472 7,472 > S13,0E H H 11938 11945,472 7,472 > S13,0E H H 11938 11945,472 7,472 > S13,0E H H 11938 11945,472 7,472 > S13,0E H H 11938 11945,472 7,472 > S13,0E H H 11938 11945,472 7,472 > S13,0E H H 11938 11945,472 7,472 > S13,0E H H 11938 11945,777 7,777 > S13,0E H H 11938 11945,777 7,777 > S13,0E H H 11938 11945,777 7,777 > S13,0E H H 11938 11945,777 7,777 > > I really wonder why Delta varies that much, and there are other transponders > in the same band which have no larger deltas then 3 MHz. The LNB drift is due to the cheap RC oscillator in standard LNB's which are temperature dependant. So, the oscillator frequency that you might experience at mid-day, might not be same as that at midnight. The capacitors are ceramic capacitors, so there isn't likely the chance of the capacitor changing it's value too much over time, but there exists other issues such as parasitic capacitances when the LNB shell looses it's hermetic seal. I have seen the drift overlapping another transponder with the stv0299 in some scenarios, but don't see how this can be fixed reliably. > > So is it at all possible to determine LNB drift in that way? > > My other device, a STB0899, always reports the set frequency. So it seems > driver dependent whether it reports the actually locked frequency found by > the zig-zag-algorithm or just the set frequency to tune to. The STV0299 blindly sets the value based on a software zigzag (due to simpler hardware), but this might not be accurate enough. On the other hand, the STB0899 internally does zig-zag in hardware for DVB-S2, and partly in software for DVB-S. In any event, the get_frontend callback should return the value that is read from the demodulator registers, rather than the cached original value that which was requested to be tuned. The stb0899 returns only the cached value IIRC. Maybe I will fix this soon, or maybe you can send a patch. Regards, Manu -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
