Dear Colleagues:
once again this group has come through with great help on my question on
"Experiment with 2H decoupling and locking" on our INOVA spectrometer.
Thanks in particular to Steve Philson, Ghirmai H. Meresi, Rajan K.
Paranji, Greg Young, Karl M. Koshlap, Eugene F. DeRose, Toshi Nishida,
and Jack W. Howarth.
In summary, the key is to use the ampmode in the pulsed setting and not
the automatic cw setting, so for our 3 channel system we need to set
ampmode='dddp'. (Yes, the forth parameter corresponds to the 3rd
channel!)
In addition, the pulse sequences have to explicitly blank and unblank
the decoupler (dec2blank() and dec2unblank()) and the lock receiver has
to be deactivated and activated during that time (lk_sample() and
lk_hold()).
In our case, we found a gating hardware problem, which leaves the
decoupler open and does not gate it even in the 'p' mode. We tracked the
problem down to the XMTR Control board and are pursuing the repair
further.
For completeness, my original message follows here, and I will collect
the explicit and helpful messages in a separate e-mail.
Thanks again for everybody who wrote to us in this issue.
Ulli
-------- Original Message --------
Subject: Experiments with 2H decoupling and locking
Dear Colleagues:
we are trying to do biochemical experiments with deuterium decoupling
and locking on our INOVA 500. We are using the diplexer provided by
Varian to combine the deuterium lock and decoupling rf (from a 3rd
transmitter channel) and the lock channel on the probe. If someone is
doing these experiments we would appreciate if you could get in touch
with us.
Our problem seems to be that already the noise level of the amplifiers
just being put into cw mode (not even putting out the decoupling rf)
makes the lock very noisy and decreases our lock level to a useless
level. Measuring on a scope we find that the noise level coming out of
the amplifiers to be about 87-90mV when initiated to cw mode, and about
nothing when set to idle or pulsed mode. The noise seems to be random
noise, but it has quite a component at the lock frequency (judged by
inserting the lock filter). Connecting the amplifier cable to the
diplexer, about 5mV survives back into the lock (receiver) side which
seems to be sufficient to saturate the lock receiver.
Specific questions therefore are:
- What noise level do you expect out of the amplifiers, when they are in
cw mode (no sequence running, no decoupling on)?
- How can we prevent the lock receiver to get saturated for this
experiment.
Again, if you are doing such experiments on a Varian System, we would
appreciate talking to you.
Thank you very much
Ulrike Werner-Zwanziger
--
Ulrike Werner-Zwanziger
Dep. of Chemistry Tel.: (812) 856-4629
Indiana University Fax.: (812) 855-8300
800 E. Kirkwood Ave
Bloomington, IN 47405
Received on Wed Oct 02 2002 - 12:29:05 MST