Electronics > Metrology

DMTD board

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Hallo all,
today I performed a very simple experiment and I believe I found the culprit why my DMTD is so unstable.

First of all, I changed the 50 Ohm input resistor for the VBB pin of the ECL gates, as suggested in an earlier post. This brought additional stability.
Then I ran some tests, during which I left the room and closed the door. After a while I went back in, and noticed that there was a sudden jump in the TI data as soon as I opened the door!
The effect was reproducible. Obviously, opening and closing the door produced a tiny air blast, that changed the temperature of the ECL gates, altering their phase.
I am annoyed that I didn't find out this earlier. The effect is reproducible when I touch the ECL chips.

I modified my entire input stage to the mixer with flying wires, and voila, now I have the desired stability of better than 1e-12 at 1 second. At least when I do this test with 2 OCXOs as signal sources at the input.
Why couldn't I find this earlier?  |O
and what surprises me even more is that the board from corby doesn't seem to have this effect - why doesn't the ECL comparator change its phase when the temperature changes?
anyways, it seems like the temperature coefficient of the input stage is crucial. The MC100EL16 ECL gate doesn't seem to be stable enough for this task.
Can anybody confirm this?


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