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
(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)