Protocol: Xmx  Sequence: xmx.c  Apptype: solidseq1d

Description: 

X pulses with interleaved acquisition and alternating phase.  Used for 
multi-pulse calibration to minimize phase transient. Usually performed 
with a liquid sample or a sample of RTV silicon rubber with slow 
spinning. Xmx can also be used to examine sampling windows and set the 
blank/unblank delays r1Xxmx and r2Xxmx. 

Xmx subtracts probe ring-down with a two-scan (0,2) phase cycle of the 
preparation pulse and the receiver.  The xmxX has zero phase for all 
scans.  For very short values of tauXxmx and when probe proton 
background is present the oscillating pattern will not be symmetric 
about zero due to a constant signal from probe ringing and background. 
Use 1 scan to see the signal without ringing. 

Additional Software:

reset_xmx - If the current experiment is Xx this macro copies the 
values of xxX to xmxX. Otherwise the values of aXxmx and pwXxmx are set 
from aX90 and pwX90. This macro is run from the protocol. 

Setup: 

Load a calibrated data set and select the protocol Xmx. For a new 
nucleus set the desired Observe nucleus select Onepul to array pwX90 
for a rough calibration before using Xmx. 

Set aXprep = aX90 and set pwXprep = pwX90. Set phXprep = 0. Set aXxmx = 
aX90 and set pwXxmx = pwX90 and nt = 2.  

Set tauXxmx = 10 us and set npaXxmx = 10.  Set r1Xxmx = 1.0us, r2Xxmx = 
0.5uus and r3Xxmx = 1.0uus.  Set rof3 = r3Xxmx on the Receiver page 
(important!!).  It may be necessary to fine adjust r1Xxmx and r2Xxmx to 
eliminate ring down from the sampling periods.

Set sw = 1/tauXxmx to obtain one point per sampling period or set sw = 
5.0e6 to observe the sampling windows. Note that because the DDR allows 
only specific dwell times, it may be necessary to choose sw first and 
set tauXxmx = 1/sw. If tauXxmx does not equal the dwell the FID output 
will not appear accurate. A sw = 5.0e6 can be used to finely digitize 
the acquisition windows and can be used for any value of tauXxmx.

Obtain 2 scans. Adjust aXxmx or pwXxmx to obtain a FID that contains 
alternating positive and zero points, "tram tracks".  Adjust probe 
tuning or spectrometer cable length to straighten the tracks.  

Use Xmx to view the sampling window that will be used for multi-pulse 
ecperiments. . Set tauXxx to a value that will create a window similar 
to that of the multi-pulse experiment (c.f. 6.0-8.0 ms for Br24q, etc).  
Note that the actual window between pulses for Xx is (tauXxmx - 
pwXxmx).  Set sw = 5.0e6. Adjust npaXxx to open or close the sampling 
window. One unit of npaXxx corresponds to 100 ns of acquisition.  The 
FID will now contain multiple points in each acquisition period and 
appear as a series of square pulses.  If the value of npaXxx is too 
large or tauXxx is too small, one will see distortion from ring-down in 
the first points of each sampling window. Determine the best 
acquisition window with the shortest tauXxx.

Parameter Groups: 

prepX:  Module:  no 
Sequence:  br24q.c      
Description:  Implements a variable length pulse to provide quadrature 
              detection about a tilted precession axis. Typically followed 
              by a windowed multiple-pulse acquisition.
Parameters:  Sequence Page
       aXprep - the amplitude of the obs pulses. 
       pwXprep - 90-degree flip on the obs channel. 
       phXprep - small-angle phase offset of the pulse. The phase must 
              be reset to zero after the pulse. 

scaleX: (processing)  Module:  no 
Sequence:  br24.c    
Description:  Shows the F2 scale factor, scalesw, for evolution of the 
              obs nuclei under a multiple-pulse waveform. 
Parameters:  Sequence Page
       scalesw - the F2 scale factor. Typically scalesw is the inverse 
              of the mutiple-pulse scale factor.  
       
xmxX:  Module:  yes
Sequence:  xmx.c 
Description:  Implements alternating X and -X pulses on obs with 
              acquisition in each window. Used for removal of phase 
              transient.
Parameters:  Sequence Page
       aXxmx - amplitude of the obs pulses.
       pwXxmx - 90-degree flip on obs.
       r1Xxmx - pre-pulse delay (similar to rof1). 
       r2Xxmx - post_pulse delay (similar to rd or rof2).
       r3Xxmx - T/R-to-rcvron delay (must equal rof3 or 2.0 us if rof3 
              is not defined). 
       tauXxmx - cycle time for one window and one pulse. 
       npaXxmx - number of 100 ns ticks in the detection window. 
       chXxmx = 'obs' must be set (not shown).
Implementation:  WMPA xmx = getxmx("xmxX");
Underscore function: _xmx(xmx,phXxmx);   phXxmx is the overall phase 
              table.  
  
