Initially, tune the receiver for maximum total power in the
traditional manner.
Some General 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.
On the 230 and 345 GHz receivers, use the
or
(Total Power vs SIS bias) and/or the
to check you are not getting the
Finally, check the
to make sure the receiver is responding to the correct harmonic.
(This is usually only a problem with the 345 GHz receiver).
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.
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.
Bias the junction to
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.
Refer to Tuning Hints.
to make sure that there is no second photon step!!
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