H.Zhou updated Feb 2011

Qtune is an alternative, graphic interface for probe tuning in vnmr software. It's been available since the early versions of the software. Due to the very different tuning sensitivity of the repaired SWP probe, it becomes necessary sometimes to use qtune to quickly tune the probe. The only issue is that good eyesight is needed to watch the displayed curve on the monitor from a distance. We'll try to possibly add a second monitor closer to the magnet legs just for this purpose. Before that, you may have to walk back and forth a bit. It is helpful to turn the computer minotor towards you for better viewing. The qtune procedure should work with other probes and on NMR400 as well.

SWP Probe Tuning


The cable connections are the same as in the normal tuning method using the tuning interface in between the broadband and 1H/19F preamp boxes. The only difference is that you do not change the tune channel and attenuator setting from the interface (see below).

The following is what you see if the P31 channel is way-off tune and match. Tuning the probe actually has two different aspects: tune and match.

Tune and Match

Tune and Match

C13 as an example

Initial look of C13 tuning graph. Match is way off. Tune isn't as bad.


First, turn the match knob (bottom section of the tune control) to bring down the dip as deep as possible. This may temporarily shift the dip off center.


Next, turn the tune knob (top control) to bring the center of the dip to match the center line (C13 frequency).


Next, fine adjust tune/match knobs to have the dip centered and deep,ideally touch the horizontal axis (this may not be possible for some nuclei).


Click "Stop Probe Tune", then click "Quit Probe Tune". Probe tuning is complete.