We have run into a problem which we believe is software
related, specific to GE GN consoles. Those of you who don't have
GN consoles may not find this too enlightening, as I will be including
a lot of details.
1) We were calibrating the 90 degree pulse width for the decoupler
transmitter by switching the J3 cable on the preamp box from dec in to
the XMTR IN port, and taking the J1 cable to a 50 ohm load. We then
used the DPULS sequence, i.e.,
1. D5, G
2. D2,D,C, L1,G
3. A,G
4. D6 JUMP TO 1
in order to trigger the decouple hard pulse. You then find the 360
pulse width (using the MC command to get around the phase instability)
and calibrate a gamma H2 decoupling field width by taking 1/360.
This all worked fine and the decoupling fields were similar to those
reported in the literature.
2) We then used the standard PRESAT sequence with the L1 saturation
power set for the decoupling field we wanted. The results indicated we
were getting an order of magnitude less power than we expected.
3) We then put a scope on the decoupler channel and monitored the output
under two conditions:
a. PRESAT, but where the observe frequency was 13C and presat freq
was 1H. The observed decoupler output at L1=60 was 1 Watt.
b. PRESAT, but where the observe and decoupler frequencies were 1H
(the normal condition). The observed decoupler output at L1=60 was
1 milliwatt.
We have three GN consoles and all of them show the same behavior.
I believe this is a software problem. We need to have the same power
output during PRESAT as we find during the sequence described in 1) above.
Any ideas?
Thanks for any help.
Vera Mainz
mainzv@aries.scs.uiuc.edu
PS I also cast my vote for Rich Shoemaker!!!