CAUTION: Because there are several ways to route RF frequencies to the sample, we will not use the word channel, which is too generic. We suggest that you avoid this word too. If the Varian manual uses the word channel be sure that you understand the context of their meaning.
WARNING: If these notes are not clear or ambiguous, or you are not sure about something, DON'T GUESS. Attaching the wrong cable to the wrong port can cause lots of damage! Contact the NMR Facility staff if you have questions or suggestions.
WARNING: DON'T adjust cabling unless there is NO experiment in progress AND all of the XMTR lights on the VT/channel display module are off. If an experiment is not in progress, but one or more XMTR lights are on, then a decoupler is on. Type dm='n' dm2='n' su to turn off all decoupling.
To set up VNMR paramters, typ rf(tn#,dn#,dn2#),
where tn# is the number of the XMTR board that will transmit
the frequency (sfrq) of the transmit/observe nucleus (tn).
For example, rf(2,1,3) tn='H1' dn='N15' will set
up the software so that XMTR2 will transmit 1H and
XMTR2 will transmit 15N. The XMTR boards can output
the following frequencies:
XTMR #1: 6 - 600 MHz
XTMR #2: 399.5-400.5 MHz (on I400) or 499.5-500.5 MHz (on I500)
XTMR #3: 6-320 MHz
The rf macro will create the parameters rfchannel
and ampmode if they don't exist in the current parameter
list (these parameters DON'T exist in the parameter lists recalled
by main menu/setup). It then sets rfchannel and
ampmode to the correct values. This macro is the same
as typing
create('rfchannel','flag') rfchannel='213' create('ampmode','string')
ampmode='cpc'.
The parameter rfchannel determines if XTMR1 (transmitter board #1), XTMR2, or XTMR3 are used for software parameters tn (transmitter nucleus frequency), dn (decoupler nucleus frequency), and dn2 (second decoupler nucleus frequency). For example, if you type rfchannel? and VNMR responds with rfchannel=312, then tn will be directed to XTMR3, dn will be directed to XTMR1, and dn2 will be directed to XTMR2.
The paramter ampmode determines if the RF amplifiers are
in p (pulse) or c (decoupling) mode (ampmode
has other options which are not relevant here) for console output
#1, console output #2, and console output #4 (see below). In
general, ampmode should have one "p" and two "c"
letters according to the following:
if rfchannel=1##, ampmode=pcc
if rfchannel=2##, ampmode=cpc
if rfchannel=3##, ampmode=ccp
Each of the
three XMTR (transmitter) boards have a "SYNTH" and "L.O."
input and a "XTMR" output. These transmitters output
the following frequencies:
XTMR #1: 6 - 600 MHz
XTMR #2: 399.5-400.5 MHz (on I400) or 499.5-500.5 MHz (on I500)
XTMR #3: 6-320 MHz
Note that all nuclear freuqncies can be generated by at least
two XTMRs, except for 19F, which can ONLY be accomplished
on XTMR1.
The SYNTH input is 10.5 MHZ greater than the frequency listed in the VNMR parameter list (i.e., sfrq, dfrq, dfrq2). This freqency is then mixed with the L.O. frequency to generate the exact frequency listed in the VNMR parameter list. Therefore, you MUST have a L.O. input connected to a XTMR if you plan to use that XTMR. For example, if you want to use XTMR3, disconnect the L.O. input on XTMR2 and put it on XTMR3.
The output of the XTMR connects to the input of the attenuator . Inside the attenuator, there are switches which redirect different inputs to different outputs. Note that attenuator input #1 is NOT NECESSARILY redirected to attenuator output #1! Output #1 is ALWAYS the high band frequency (1H or 19F) and outputs #2 and #4 are ALWAYS a lowband frequency (6-320 MHz, output #3 is not used). These outputs are directed through amplifiers in the back of the console, and then leave the console in thick cables.
| VNMR parameter | |
|---|---|
| tn= 1H or 19F | H BAND NC line (usually a thick cable) |
| dn or dn2 = 1H or 19F | H BAND NO line (usually a thin cable) |
| tn = lowband nucleus | B BAND NO line (usually a thick cable) |
| dn or dn2 = lowband nucleus | B BAND NC line
(usually a thin cable) |
The tune module "XMTR" ports receive the probe interface outputs. The frequencies then leave the tune module through the "probe" port, which should then be connected to the proper frequency filter, which should then be connected to the proper port on the probe. A console output does NOT have to go through the tune module: the console output can be directly connected to a filter, which is then connected to the probe. However, the observe frequency tn MUST be connected through the tune module. Also, if you want to tune the probe using a particular console output, that console output MUST be connected to the tune module during tuning. You must also place the proper 1/4 wavelength cable from the 1/4 wavelength port to the broadband preamp port on the broadband side of the tune module. Each 1/4 wavelength cable is marked; also keep in mind that lower frequencies have longer wavelengths, so lower frequencies use longer 1/4 wavelength cables.