Unstable Almazny output

[Spaqin]

One of the users of this card has reported unstable output of Almazny being unstable (see attached video). The output from the channel should be at 4.7GHz, and corresponding Mirny frequency of 2.35GHz is correct, and that signal is clean.

https://user-images.githubusercontent.com/1278433/171342959-8647d53e-d0ae-4380-883e-410f5330e0b7.MOV

The scope used in the video is Tektronix DPO 71254C, which is rated up to 12.5GHz. I have tested the outputs of the card before with a BladeRF, which won't show exactly how the signal looks. What could be the problem?

[gkasprow]

We observe similar issue when measuring RF with scope. It looks like 2.4GHz ISM or signal from BTS which is picked up by the cable. To verify this, disable Mirny output and see how the signal looks like.

[a3modgil]

We observe similar issue when measuring RF with scope. It looks like 2.4GHz ISM or signal from BTS which is picked up by the cable. To verify this, disable Mirny output and see how the signal looks like.

How could we go about doing this?

[gkasprow]

@a3modgil can you simply disable Mirny RF switch and make the screenshot? Just keep the setup, cabling and configuration and do two measurements with RF switch enabled and RF switch disabled. How to cope with such interference? Use better RF cables. Why are you working with such low signal amplitude?

[a3modgil]

@gkasprow The signal amplitudes are not decided by us, we are testing our crate with a tester file supplied by M-labs: https://github.com/m-labs/artiq/blob/master/artiq/frontend/artiq_sinara_tester.py

During the test, even when the attenuators are turned off and the amplitude is higher, the noise/shakiness persists and the wave produced is not a sine wave (similar to what is produced in the video above), which was what we thought should be outputted, as the Almazny is supposed to only amplify the frequency and not change the wave shape from the corresponding mirny port.

[gkasprow]

Please show me the screen with Mirny RF switch off.

[a3modgil]

https://user-images.githubusercontent.com/78876933/172689009-0256dfac-a1ee-4488-9796-bd697414bd46.MOV

This is RF0 with the attenuator at half power. The mirny outputs have been disabled.

[gkasprow]

It looks like the classical ground loop issue. It seems to be not a signal generated by Mirny but picked up by the setup. What you see is 5G Wifi or similar transmission.

[a3modgil]

How do you recommend we go about fixing this issue?

[gkasprow]

Use better SMA cables and check the grounding scheme to make sure CMCs are used on all power cords.

[jordens]

Is this resolved or is there anything to be done?