CPMG pulse program with HADC digitizer and digital filtering for AVANCE AQX.
Contribution of Y. Millot

J. T. Cheng and P. D. Ellis ( J. Phys. Chem. 93, 2549-2555, 1989) studied the adsorption of Rb⁺ to γ-alumina using CPMG echo train pulse sequence. The Fourier transform of the fid followed by the train of m echoes is a spikelet spectrum. The latter has a better signal-to-noise ratio than that from one-pulse experiment.

In digital filtering experiment, the last echo is truncated if the number of echoes m is small.

Code for Avance AQX NMR spectrometers with xwinnmr 2.6 operating system

  ;Carr-Purcell-Meiboom-Gill echo train acquisition with digital filtering
  ;and HADC digitizer
  #include <Avance.incl>
  define delay dx
  define delay px
  define loopcounter tdov
  "tdov = td*decim/2"
  "l1 = tdov/(2*l3 + 1)"
  "l2 = 2*l1"
  "l4 = l3*l2 + l1"
  "l5 = l3*l2 + l1"
  "dx = dwov"
  "px = dwov"

          ze                         ; clear memory, new data replace old data
  start,  d1 pl1:f1                  ; recycle duration.
          p1:f1     ph1          ; 90° pulse with x phase.
          d11                        ; echo delay d11 + d14.
          d14                        ; echo delay d11 + d14.
          p2:f1     ph2          ; 180° refocussing pulse with y phase.
          d11 adc   ph31             ; echo delay d11 + d14.
          d14:e     ph0    syrec     ; echo delay d11 + d14.
  fid,    dx                       ; dx + px, the dwell time for the external dwell-pulse.
          px:x                     ; external dwell-pulse for the fid data digitizing.
          lo to fid times l1       ; loop for the fid data digitizing.
  nbecho, d11:e                      ; echo delay d11 + d14, sytra not required.
          d14:e                      ; echo delay d11 + d14.
          p2:f1:e   ph3          ; 180° refocussing pulse with y phase.
          d11:e            syrec     ; echo delay d11 + d14.
          d14:e     ph0              ; echo delay d11 + d14.
  echo,   dx                       ; dx + px, the dwell time for the external dwell-pulse.
          px:x                     ; external dwell-pulse for an echo data digitizing.
          lo to echo times l2      ; loop for an echo data digitizing.
          0.1u
          lo to nbecho times l3  ; loop for the echo train acquisition.
          rcyc=start             ; loop to start, ns times for averaging.
          100m wr #0             ; delay for disk I/O, store signal.
  ;-------------------------------------
  tmp1,   100u
          lo to tmp1 times l4    ; provide the oversampling 
                                 ; time domain size tdov nearly = l4.
  tmp2,   100u
          lo to tmp2 times l5    ; provide the time-domain size td = l5.
  ;-------------------------------------
  exit                           ; end of the pulse program.

  ph1  = 0 0 1 1 2 2 3 3                   ; f1 channel p1 pulse phase
  ph2  = 1 3 2 0 3 1 0 2                   ; f1 channel first p2 pulse phase
  ph3  = 1 3 2 0 3 1 0 2  3 1 0 2 1 3 2 0  ; f1 channel second p2 pulse phase
  ph31 = 0 0 1 1 2 2 3 3                   ; receiver phase
  ph0  = 0                                 ; receiver reference phase

  ;pl1:    f1 channel power level for p1 and p2 pulses
  ;d11:    10u
  ;l1:     number of digitized points for the fid
  ;l2:     number of digitized points for an echo
  ;l3:     number of echoes
  ;dx + px = 2*dwov: dwell-time for the external dwell-pulse
  ;ns = 16*n
  ;dw = dwov*decim
  ;aq = dw*td = 2*dwov*tdov