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 Mon Sep 30 2002 - 09:26:18 MST