I was asked by Eugene Kwan to explain how the encoded F1 frequency is broug=
ht down from radio frequency to audio frequency, since there is no analog "=
receiver" in the F1 dimension that can mix signals to subtract out the carr=
ier frequency. His idea, which sounds good to me, is that the RF signal is=
radically undersampled and aliases all the way down to audio frequency. T=
he problem that I have with that is that I know from experience that changi=
ng the 2nd channel carrier frequency in a heteronuclear 2D experiment (Vari=
an dof/dfrq, Bruker o2/sfo2) moves the peaks up and down in the F1 dimensio=
n. So the data behaves as if there is a carrier frequency in F1 that is be=
ing subtracted from the observed radio frequency, but there is no hardware =
explanation for this. I don't believe that it's a software "trick" because=
I've seen it even in Bruker AM systems, and also when I process data using=
Felix with my own processing macros.
If anyone has a good explanation of how this works, hopefully understandabl=
e by regular people, I would greatly appreciate it.
Neil
Neil E. Jacobsen, Ph.D.
NMR Facility Manager
Old Chemistry Room 119
Department of Chemistry and Biochemistry
University of Arizona
1306 E University Blvd.
Tucson, AZ 85721
Phone: 520-621-8146
FAX: 520-621-8407
Received on Wed Apr 20 2011 - 06:10:33 MST