Lately, I have noticed a problem with an unstable lock signal at high
temperature (<90C). The lock signal appears as if it is being
saturated (even at very low lock power settings) or behaves
irratically. I thought that the problem originated with the shim set
at high temperature however, the current through each of the shims
seems to be very stable. I put in a different probe (5mm
broadband) and the problem seemed to disappear, therefore I assume
that the problem is with my inverse broadband probe. There are
however no visable problems in the probe. I have also eliminated the
the question as to whether the sample is bouncing up and down in the
probe as the problem occurs even at very low VT gas flow rates and
also there is no spinning problems.
Has anyone encountered any similar problems? Are there components in
the lock channel of an inverse probe that are suseptable to
temperature variation?
Glenn Facey
NMR Facility Manager
University of Ottawa