Hi, I am working on an simulation for 25G operation, the results is targeted to meet CEI 25G LR mask. An interesting thing I found in OIF-CEI 25G mask is the method used to power sum the crosstalk sources, actually the same method use also for IEEE 10GBase-KR standard. For example, If I have two crosstalk source, the equation should be like below: PSXT=-10*log10(10^(-Xtk1/10)+10^(Xtk2/10)) But my question is, in SI area, our S-parameter is calculated using Voltage rather than Power, it means we calculate the value use S12 *log10(Vout/Vin). So the problem happened when we use the equation above, two -40dB crosstalk add up to PSXT=-10*log10(10^(-40/10)+10^(-40/10))=-37dB While the reasonable value should be -40dB corresponding to 0.01, and two of them makes 0.02, so PSXT *log10(0.02)=-34dB Does anyone know the trick behind the equation? Or what's wrong with my understanding? Thanks. Bruce ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: //www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List forum is accessible at: http://tech.groups.yahoo.com/group/si-list List archives are viewable at: //www.freelists.org/archives/si-list Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu