SIS Mixer tuning

Aleks ran the auto-tuning function of the SIS software (CANbus).  The voltages determined were just slightly smaller than a few days ago, but there is also more LO power coming in (4 uAmps additional current).  The auto-tuned voltage is 8.80V, (measuring 61.3 uA) for the cable labeled lcp and 9.00V (measuring 57.5 uA) for the cable labeled rcp.

Preparing now for Y-factor test. 

Link to spreadsheet of data

We performed a Y factor test on the channel labeled LCP on the bench.  First we went through Bias Voltages at the LO power that produced around 62uA of current through the SIS junction.  Next we tested a subset of Bias Voltages where we tuned the LO power down such that the current in the junction was roughly 56 uA and then 40 uA.  Results of that test in the image below.

While performing the test we noticed the 10 MHz signal was very clear in the oscilloscope.  We also noticed that changing the LO power such that the current in the junction was nearly 62 uA (the blue curve) reduced the power of this 10 MHz signal.  It seemed to be the "sweet spot" for minimizing this signal.

The best Y factor was 2.19 (lowest T_RX was 106 K), which was achieved with Bias Voltage of 8.6 and an LO power tuned such that the current in the junction was near 62 uA.  The auto-tuning led us to 8.8V at 62 uA.

We came back to the experiment an hour or so later, and checked the Y factor again and it was quite poor, even at the bias voltage and LO power that produced the minimum, and it gave a Y factor of 1.99 and T_RX of 140.

There is a lot of variability here, tough to get clear values and minimums.

Aleks reports in his lab notebook that in initial set up a few days ago they achieved a Y factor of 2.5 (RCP) and 2.22 (LCP).  We were able to get as high as 2.19 with LCP today. 

Again we are reporting LCP and RCP as the label names coming out of the total power box (truthfully on the sky because of the mirrors these are flipped).