General 345 GHz Tuning

345 GHz Receiver Tuning in Detail

Because of it's very large tunable (280-430 GHz) There is a potential trap when tuning this receiver. With the older Millitech X4 multiplier, it is highly likely the Local Oscillator chain puts out both the 4th and 5th harmonic, and you may not initially notice this. If you are tuned to the fifth, rhather than the fourth harmonic, you should be aware that this easily manifest itself by high system temperatures on the sky. If you suspect you are in this mode, try to observe a source with a strong line in the expected 4th multiple band. You can also see from the I/V curve whether the junction is responding to the 4th or 5th harmonic. Once you have tuned up, and have some power on the junction, go to and check the frequency it claims to be responding to.

  1. There are three Multipliers for this Receiver:
    • 280-330 GHz, Millitech, X4
    • 320-380 GHz, Millitech, X4 (1990 model, Both 4th, 5th harmonic)
    • 320-380 GHz, Millitech, X4 (1999 model, no 5th => more RF Power for 4th harmonic)
    LO Bias: Do not exceed 4 mA on Multiplier Diode
    Rx Tuning Procedure: Refer to the Receiver Tuning Cookbook.
  2. Bias the junction to
  3. Set the Magnetic field Current to about 20-35 mA (+ or -).
  4. Monitor the and recheck from time to time that the is still in lock.
  5. Optimum junction current is typically about 9-11uA.
  6. From now on the tuning process is iterative. That is, optimize the SIS current by adusting the:
  7. When finished tuning, make a final check of the Any Josephson oscillations will seriously effect the receiver stability.
  8. Make sure the is set to 2.1-2.2 mV.
  9. Refer to Tuning Hints. to make sure that there is no second photon step!!
  10. Finally it is best to put the SIS bias voltage on a flat spot of the P/V curve (dP/dV=0). This is critical because in this way the
  11. Please do remember to the total power on the Sky when all is set and done and you are ready to observe! This guarantees that the AOS are presented with a fixed IF power level.
  12. Last but not least, do perform standard Y-factor measurements to make sure that the receiver properly works
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    Web Page created and last updated on March 5, 2001, by: Jacob W. Kooi