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sinara-hw / mirny

4-channel Microwave synthesiser
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Output crosstalk due to lacking isolation #36

Closed nkrackow closed 8 months ago

nkrackow commented 1 year ago

The outputs of current Mirnies V1.1 suffer from significant crosstalk: PNG1

Pushing on the PCB close to the front panel makes the crosstalk vary by more than 10 dB. The SMA shield is shorted to the front panel at DC.

This implies that there is a problem with the front panel, probably the SMA pins making connection. The same issue appears on other high frequency sinara modules: https://github.com/sinara-hw/Urukul/issues/68

@gkasprow @akaminska

kaolpr commented 1 year ago

I believe SMA shield is just shorted to FP in a defined assembly variants: image image

gkasprow commented 1 year ago

yes, but the impedance of short-circuit may be non-negligible for 1GHz and above

jordens commented 1 year ago

It does have to do with the panel. Slightly bending the PCB away from it with a finger significantly changes the crosstalk.

akaminska commented 1 year ago

We will try to re-create and investigate the problem

gkasprow commented 1 year ago

To do this, we need more info about the setup. Preferably some photos depict how cables are placed.

jordens commented 1 year ago

@nkrackow sent a photo to @akaminska AFAIK

nkrackow commented 1 year ago

Yes, I put them here again now. I don't think we've attached anything in a strange way. Simply the output of a Mirny to a spectrum analyzer. We've seen the most crosstalk between roughly 1-2 GHz, above and below it was better. Pressing on the PCB close to the front panel (area central in the first picture) has quite an effect on the crosstalk.

IMG_20221220_173127 IMG_20221220_173116

gkasprow commented 1 year ago

we plan new revision. What if we remove the assembly variant and connect the SMA connectors to solid GND?

gkasprow commented 8 months ago

added direct connection like in Urukul