I/V Sweep Window

With the advent of RF tuned junctions it is now quite realistic to get mixer conversion gain. Although this will give very sensitive performance it is not neccesarily a stable mode of operation and should be avoided. Ideally the receiver should be run with near unity conversion gain (or loss). Conversion gain regions(on the 230-492 Rx's) can be spotted by negative to infinate slopes on the LO pumped I/V curve. The LO pumped slope should ideally be slightly positive (nearly flat) , and never negative! Typically, after peaking the total power, go into the IV sweep mode, and look to see if the slope is negative, flat or positive, and whether there is a second photon step.

If the slope is negative, stay in the IV sweep mode, and gently adjust the E-plane (or alternatively the backshort) tuner until the slope changes to flat to slightly positive. The second photon step can be seen both in the IV sweep, as a second step to the left of the main one, and also in the B-field display mode, as a second bump to the left of the main one.
NOTE: A numeric value for the slope around the bias point can be abtain from the SLOPE button in the Rx control window.

There are two ways to display the SIS current as a function of bias.

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Web Page created and last updated on March 5, 2001, by Jacob W. Kooi