Initially, tune the receiver for maximum total power in the
traditional manner.
Check the magnetic field. Turn on the magnetic field, and either look at
the
or
to adjust the field strength to minimise/suppress the general Josephson
structure and give the
Some critera
LO must be on the receiver to set the magnetic field.
Minimized the magnetic field (current) since it suppresses the superconducting
energy gap, which results in degraded receiver performance.
492 GHz Receiver Tuning in Detail
There are three Multipliers for this Receiver:
440-510 GHz, RPG Physics, X6 (1990 model, 4 tuners worn out but RF performance ok)
380-440 GHz, RPG Physics, X5 (1999 model, 3 tuners, refer to data sheet for settings.
Set the Magnetic field Current to about 20-35 mA (+ or -).
Monitor the
and recheck from time to time that the
is still in lock.
Optimum junction current is typically about 9-11uA.
From now on the tuning process is iterative. That is,
optimize the SIS current by adusting the:
When finished tuning, make a final check of the
Any Josephson oscillations will seriously effect the receiver stability.
Make sure the
is set to 2.1-2.2 mV.
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
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.
Last but not least, do perform standard Y-factor measurements to make sure that the receiver properly works