Johannes Stezenbach wrote: > On Sat, Sep 29, 2007, Manu Abraham wrote: >> Johannes Stezenbach wrote: >>> - LNBs have a constant error plus a temperature drift >>> (e.g. +/-1MHz error, +/-3Mhz drift for a temperature range >>> of -40 ... +60 °C -- cheap no name equipment usually worse) >> This is the old LNB, the one's we use are generally based on PLL's >> have some 15 - 20k drift > > If you make that 20kHz per °K then it's about the usual range > for Ku Band, maybe slightly better than average. > (An LNB with +/-20KHz drift over the full temperature range > would be ridiculously expensive.) ACK didn't account for the / K. But still for a LNB with 27 K, It amounts to around +/- 0.5MHz Which is still quite small for a 5 - 10 MHz window. As you said, maybe there are really bad ones with +/-1MHz drift, but i think +/-3MHz is a bit too exaggerated figure > > Don't forget that your tuner also has maybe +/-50ppm tolerance. > The errors can add up. Let's assume with a step size of 1MHz at the most max. 50ppm (error even when summed) is too small even for the largest 1MHz step, comparing to +/- 0.5Mhz drift. Manu _______________________________________________ linux-dvb mailing list linux-dvb@xxxxxxxxxxx http://www.linuxtv.org/cgi-bin/mailman/listinfo/linux-dvb
