Dear AMMRL,
many thanks to all those who responded to my problem described
below. The overwhelming consensus of respondents was that the
problem was due to a frequency synthesizer problem. This proved to
be the case. We are now using the third channel PTS to drive the
second channel and all is well (since we almost never do triple
resonance on this instrument).
One additional note provided by the respondents is that the problem
could be the small card that hangs off the back of the PTS - rather
than the PTS itself- but we didn't investigate that.
Jeff
>Date: Tue, 22 Apr 2008 11:40:19 -0700
>To: ammrl_at_ammrl.org
>From: Jeff de Ropp <jsderopp_at_ucdavis.edu>
>Subject: AMMRL: missing frequencies problem on VNMRS-600
>
>Dear AMMRL,
>we are having a problem with "missing frequencies" on the X-channel
>of our VNMRS-600.
>
>This shows up in a couple ways. First, we are seeing a large number
>of U-shaped dips in the tune display that obscure our ability to
>tune the probe for certain nuclei, for example Sn-119.
>I have posted a screen capture of the problem:
>http://www.nmr.ucdavis.edu/ammrl/mTuneScreen.pdf
>We have tried the obvious things like switching probes and replacing
>the cable to the probe. The problem is present with different
>probes. The problem only occurs on the X-channel; proton is fine.
>
>Second, if we use an external scope we can tune the probe fine to
>the nuclei "obscured" in mtune, for example Sn119. However when we
>try to acquire an Sn119 spectrum we see nothing, even for a
>concentrated standard sample we normally see on one scan. So the
>problem is more than just the tune display, certain frequency
>regions are now "gone" and not observable.
>
>Any ideas on solving this would be greatly appreciated.
>Jeff
>
>
>Jeffrey S. de Ropp, Ph.D.
>NMR Facility
>UC Davis
>One Shields Avenue
>Davis CA 95616
>jsderopp_at_ucdavis.edu
>530-752-7677 office
>530-752-6480 MS1-D Lab
>530-752-5682 600 MHz Lab
>530-754-8238 Chem NMR Lab
>530-752-3516 Fax
>NMR Facility Web site URL is:
>http://www.nmr.ucdavis.edu/
Jeffrey S. de Ropp, Ph.D.
NMR Facility
UC Davis
One Shields Avenue
Davis CA 95616
jsderopp_at_ucdavis.edu
530-752-7677 office
530-752-6480 MS1-D Lab
530-752-5682 600 MHz Lab
530-754-8238 Chem NMR Lab
530-752-3516 Fax
NMR Facility Web site URL is:
http://www.nmr.ucdavis.edu/
Received on Fri Apr 25 2008 - 16:04:39 MST