Hallo all I've got a question concerning the DMTD methodology. I want to compare different oscillators to each other in a 3-cornered hat fashion such that I can work out (hopefully at least approximately) their stability. For this, I thought about the attached schematic. I plan to connect my three oscillators under test to three mixers and use a common transfer oscillator for all three. In my opinion, a time-tagger instead of a TIC would allow me to compare any two of the three oscillators: 1 vs. 2, 1 vs. 3 and 2 vs. 3. With this, I could determine the Allan variances of the different combinations and then solve the equation system for the Allan variances of the individual devices. Would this scheme work? I would like to use a STM32 microcontroller as a time tagger. When it is clocked by 10MHz only, it would provide 100ns time tag resolution, but apparently, this should be enough: If I compare 5 MHz oscillators and heterodyne them to 5 Hz, the resolution should be somewhere at 2e-13 (for tau=200ms). And I think at tau=1sec it would be five times higher, i.e. 4e-14. Is that right? In this case, I wouldn't even need a TDC7200 as an interpolator. On the other hand, I could use the STM32's internal PLL to generate a 50MHz clock for the timers, and therefore increase the time tag resolution to 20ns. I think the attached schematic should definitely work, but I am unsure whether this is a "smart" idea. Maybe there are better methods to compare 3 oscillators directly. Any hints for this?
many thanks. Tobias HB9FSX [image: dmtd.png]
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