Hello Salva, Due to Si5351 out of stock, we started to use MS5351M to replace SI5351A-B-GT. In order to obtain the widest possible range of measurement frequencies for the NanoVNA, we have extended some usage ranges beyond those specified in the Si5351 manual. Although the performance specified in the MS5351M manual is almost identical to that of the Si5351A-B-GT, they differ slightly for the parts that go beyond the manual. Simply put the MS5351M has a slightly higher VCO frequency than the Si5351, the MS5351M has a steeper square wave edge, and the MS5351M has slightly lower phase noise than the Si5351. With targeted software adjustments, it is possible to get slightly better results with the MS5351M than with the Si5351. Since the frequency range of the VCO is slightly different, the frequency points for switching different divider are different when using Si5351 and when using MS5351, so if the software's signal generator MODE is different from the actual chip installed, it will generate some anomalies around the divider switching frequency.
You can set the measurement frequency to 50kHz-900MHz and check if some abnormal spurious is generated. If there are multiple abnormal spurious, the signal generator mode of the software is not the same as the actual installed chip. On our NanoVNA-H and NanoVNA-H4, if MS5351M is used, we add the MS suffix to the version number on the label of the backshell, such as 3.6_MS or 4.3_MS.
