Thanks to those of you whose suggestions required
more hardware/software (as in grey matter) than available.
For anyone with a similiar problem in the future I am summarizing
the responses.
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Hi,
If you have an RF source, a scope and a power splitter, it is easy to
tune the probe on the bench and then tweak it in the magnet. I say on
the bench because you stand up and take your time about it. We do this
for all new nuclei with which we have no experience. It makes life much
easier.
Good luck.
Sara Kunz
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Carl,
If it is possible to use Qtune on your system try it. Look in the
Varian User Commands manual for details. With the added information
from the frequency sweep you should be able to figure out what is
going on.
David Redwine
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Well B11 is in the ranks of easy nuclei.... Are you sure that there isn't
something wrong with the probe. Can you wobble it so as to see the precise
tune/match realtionship? I am puzzled by this as B11 can be got on all the
standard Varian BB porbes that I have ever seen/used.
Best regards
marc
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First of all some nmr probes have Boron glass inserts in them around the
saddle coils. See what type you have. Use a symmetric, four-coordinate
Boron sample to get a sharp signal (< 100 HZ). Keep in mind that higher
magnetic fields increase the quadrupolar relaxation times in nuclei like
B-11 and B-10.
I have studied boron pyrazole and imidazoles and have some expertise with
this nucleus.
Dr. Alan Kook
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This sounds like a 300 MHz nmr?
We are able to do this with the stick out although the Tune-down is
essentially all the way out (single digits). I found this by using
our sweeper and reflection bridge and I suggest you use a similar
arrangement to see where you really are. Will the "qtune" program
work for you?
cdr
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If you are doing this on an Inova I suggest you use qtune to get the
probe tuned in close to Boron-11 and then switch to the meter.
-- Greg---------------------------------------------------------------------------- -------------
What vintage is your spectrometer? Do you have software with the qtune option (and the appropriate hardware)? This function allows you to observe the resonance as one would with a sweep generator and a reflection bridge. That way you can find out your tuning range of the probe with each of your stick capacitors (and, most importantly, it should help you tune to the B11 frequency). Actually, upon further reading your message, you must have an older system (the new ones have a digital readout for reflected power and have an attenuation scale that goes to 9).
Otherwise, you can try the following. If you know that you can tune to a frequency that is close of the B11 frequency, go ahead and do so. Then, you just change the spectrometer frequency by 1 MHz or so toward the B11 frequency and then retune. You can use a series of these frequency changes until you get to the B11 frequency. You may be able to make greater changes between retuning - I guess you will find out if you try this.
I hope this helps.
Regards,
Joe
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Hi Carl, I have had good success following the tuning procedures in the Varian NMR Probes Installation Manual. There is a special section for your application on pg. 67(pub. No. 01-999034-00, Rev. B0798). We have tuned nuclei in that range, but not B11 (we have a special Boron-free probe on a dedicated spectrometer for that). In any case, when you get it tuned, I highly recommend counting off the turns for all controls and recording this data for future reference. Do not rely on the probe's counter alone. The Autoswitchable probes can be a pain, but once you have it right, they are repeatable. Good luck, Jerry
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