Receiver Tuning Cook Book

  1. First, select the line you wish to look at, using the LINE command in UIP. If you are observing a source with large velocities slew to your source with the OBS command before starting to tune the receiver.
  2. Go the the receivers and check that the attenuator in the is fully closed (anti-clockwise, all the way out) so no power is incident on the multiplier.
  3. The Gunn lock frequency is displayed on the Antenna display screen and is called F-lock. Look up the for this lock frequency. These are located on the tables stuck to the sidecab wall near the entrance door or allidade.
  4. Turn the SWEEP switch on the Gunn section of the so you can get a clean lock (easier to get a good lock this way).
    Now you MUST tune both the GUNN Tuning micrometer and Backshort to the tuning chart values, and then tweak them (mainly the tuning micrometer) to get the PLL to lock. Just tuning the tuner till it locks without adjusting the power backshort to the correct position could result in you locking at the incorrect frequency ...... and you would never know, except your lines wouldn't show up.
  5. When locked, check that the gunn control voltage centered in its range, and then the green lock LED better stay on! The sweep function of the PLL sweeps the bias of the Gunn and tries to keep the Gunn Oscilator locked as it drifts with time.
  6. Now begin to tune the
    The general idea is to maximize Total Power and obtain a positive slope on the IV curve: Start by setting Vsis=2.1mV, and by putting some (20-40 mA) of magnetic field on the junction.
    Open the attenuator, watching for or by monitoring the
    For all receivers the first step is to tune the so that some power is visible on the Adjust the (except for the 850 GHz Rx which has no tuners), trying to peak up the Total Power (O-scope or handheld). Turn the backshort right in to zero, then turn it out till you see a peak in the total power and/or SIS junction current. This first peak is likely to be the correct one for the backshort. If the junction current is very high (above 13 microamps for the sidecab receivers), attenuate the LO signal. Now adjust the Again, turn it to zero, then start turning it out. You will see the total power will not vary for a long time - it is on a plateau. Then it will drop somewhat and rise sharply to a peak, then drop again and rise to another peak. It is probably best on one of these 2 peaks. Iteratively tune the micrometers to peak the on the SIS junction, and then repeat tuning the Receiver.

    Note that Access to these tuners is quite difficult if the zenith angle is less than around 30 degrees. Also please be very careful when tuning the Backshort and E-plane tuners as they connect to the mixer via a thin piece of which is very fragile.
  7. Once you have some sort of receiver response, you should, check the magnetic field setting. Press the this will start a of total power versus junction bias on the Turn the voltage on the magnet up from zero and watch the O-scope display. You should see the curve become more and the general amplitude can drop significantly. The aim is to set the magnet current to minimize the total power, which means that the Josephson noise is suppressed.
  8. Continue tuning the receiver for optimum performance. After peaking the total power, press the softkey and observe the IV sweep on the or the Look to see if the slope is negative, flat or positive. If it is negative, stay in this IV sweep mode, and gently adjust the E-plane (or alternatively the backshort, thought the E-plane may work better) tuner until the slope changes to flat to slightly positive. (Refer also to the section on or see the IVsweep menu or Receiver Control menu below for more detail on this. Set the LO attenuator so that you get about of current on the junction. If you draw too much current on the SIS junction, the receiver may be unstable. If you see bad baselines, check the current - if it is much above 12 microamps turn the up to reduce the SIS current to something less than 12 microamps.
  9. 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
  10. Last but not least, 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.
    | Receiver Index | Rx Tuning Menu | Receiver Control Menu | B-field Menu | I/V sweep Menu |
    Web Page created and last updated on March 22, 2001, by: Jacob W. Kooi