Andy Walls wrote:> On Mon, 2008-10-27 at 15:03 +0100, Georg Acher wrote:>> On Mon, Oct 27, 2008 at 10:37:52AM +0000, Morgan Tørvolt wrote:>> >>> As I used to work with satellite signals on an earth station, and was>>> responsible for the development of measurement techniques, I thought I>>> should join in here for some hopefully revelaing info.>>>>>> I am guessing here of course, but I believe that there is no real SNR>>> measurement in any of the tuners available for computers. True, most demodulators do provide a CNR from which SNR can becalculated out. CNR is measured from the early stages, while SNR ismeasured out from the final stages. >> My guess is that it is possible. Actually, it is quite easy for QPSK ;-) You>> only need to calculate the distance of the IQ-value from the ideal symbol>> center ( (sqrt(0.5),sqrt(0.5)) or whatever) after the>> rotator/retiming-block.>>> > Isn't that just Error Vector Magnitude (EVM)? Not only that, by the time a driver reads that through a slow bus suchas I2C (of course not to be forgotten about other delays: inherent todemodulator internals) though it can be used to evaluate SNR on thedemodulator IP core, the events being at 2 distinct points of time as itis not RT wrt the driver, i guess it makes no sense. Regards,Manu _______________________________________________linux-dvb mailing listlinux-dvb@xxxxxxxxxxxxxxx://www.linuxtv.org/cgi-bin/mailman/listinfo/linux-dvb
