Many thanks to George Gray, Rolf Kybuz, Jerry, Hirschinger, Andrew Fowler, Wei Wycoff, Quincy Teng
and Deryck Webb for all providing input on this problem and pointing to the eventual solution.
It turns out that there are a number of 4th channel amplifier configurations available on INOVAs.
In one configuration there is a separate fourth channel amplifier. In this case, having an ampmode
setting of 'dddp' is correct for 2H decoupling in that it blanks the deuterium decoupling when not
pulsing in order to prevent interference to the lock.
In another configuration the third and forth channels share an amplifier, and having the fourth
channel set to 'p' seems to put the third channel into pulse mode as well and will prevent
decoupling. The solution in this case is indeed to destroy the ampmode parameter if you don't need
2H decoupling.
Our system uses the "lock decoupler" and in this case a combination of a bad rftype parameter and
ampmode = 'dddp' created the same problem. For this type of system, rftype for the fourth channel
should be set to 'l' specifying the lock decoupler. However, on our system it had been set to 'd',
possibly during a VNMRj upgrade since it was set correctly to 'l' at installation and was correct in
the previous VNMRj version -1.1D (Gremlins???). We hadn't noticed, since we haven't done any 2H
decoupling. With this mis-configuration, setting ampmode to 'dddp' will also cause 15N decoupling
on the third channel to fail. The BioPack BPsetampmode macro will detect the presence of the lock
decoupler and destroy the ampmode parameter (it's not needed for lock decoupler) but *only* if
rftype is configured correctly.
We also noticed that on our system that amptype for the forth channel was set to 'n', specifying a
shared amplifier, and has been since installation. Amptype should probably not matter for the lock
decoupler since it has its own dedicated amplifier, but I suspect that it may have been contributing
to the problem by fooling the software into thinking there was a shared amplifier. (Haven't had a
chance to actually check this out).
Nevertheless, if rftype is set correctly for the lock decoupler, then amptype becomes irrelevant.
Thanks for the help.
-Kirk
Kirk Marat, Ph. D., NMR Facility Manager
Dept. of Chemistry
University of Manitoba
Winnipeg, MB, R3T 2N2, CANADA
C#, What C++ should have been
ph. (204) 474-6259 FAX: (204) 474-7608
kirk_marat_at_umanitoba.ca
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Received on Mon Feb 23 2009 - 12:39:34 MST