Tuning Hints

With the advent of RF tuned junctions (230-665 GHz Rx only!) it is now quite realistic to get mixer conversion gain. Although this will give very sensitive performance it is not 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 (nearly flat), or Typically, after peaking the total power, go into the mode, and look to see if the slope is negative, flat or , and whether there is a
NOTE: A numeric value for the slope around the bias point can be obtained from the SLOPE button in the

If the sub-gap slope is negative or very large go into the Rx control window and adjust either the tuner while keeping a careful eye on both the Total power and SIS current Bargraphs. The Total Power value will drop dramatically in most instances, but the the SIS current will should the same or perhaps slightly increase. The operating point is typically just before the SIS current degrades. At this point the SIS mixer gain is reduced to slightly less than unity which provides a stable operating point for the mixer.
At this point either go back into the mode and study the pumped sub-gap slope on the scope (I/V display), or press the Slope button in the to obtain a numeric value.

Alternatively you can 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.