>They could be acoustic side bands caused by noisy VT air flow
>in the coil/sample area of the probe. Basically, the probe is acting
>like a flute, but the pitch is a little off for modern orchestral playing.
>Try varying the VT air flow rate. We had this problem on an early Nalorac
>triple resonace probe, (which they subsequently corrected). Supposedly
>this problem has also been seen on certain Varian probes.
That brings to mind something that I went through myself with Varian probes:
if you are using N2 for low-temp VT gas feed and compressed air for air
bearing, probe housing cooling, and spinning, it makes a gas cocktail in the
probehead that has fluctuating susceptibility and causes problems like this.
Presumably the same effect would manifest on other probes as well, but
Varian people confirmed the cause for me years ago. Switching to N2 feed for
everything solved the problem.
Bill
William C. Stevens, Ph.D. NMR Facility
Director Southern Illinois University
Carbondale, IL 62901-4405
wstevens@siu.edu
wstevens@intrnet.net voice: 618-453-6498 fax: -6408
http://www.siu.edu/departments/shops/bill.html home:618-457-8385