Thank you for all the tips and video's!

I started practicing vibrato mid december2020 / I agree with ears being important for studying. I am nowhere near the finish line though. 

I notice a firm bow is one of the things to hold on to. to at least make it sound like an instrument. : ))

But my progress is slow and to me hardly noticable 

I DID use a machine to track;  I recorded my notes to melodyne to count the frequency /second. I went up from 3 to a little over 4 (peaks or trougs) per sec (in ONE MONTH, thats feels as very little progress). I also recorded some pro vibrato into melodyne and these were about 5-6/sec. 

I know vibrato has many different shapes and frequencies. But the slow vibrato I am practicing still sounds nothing like the real thing. Ill keep working on it.