You should tune the probe before acquiring simple 1D spectra if optimum signal to noise is desired. Probe tuning is also important for obtaining optimum signal to noise and avoiding artifacts in other more complex experiments.
Tune the probe before you shim.
Load a parameter file that includes the desired tuning frequencies and enter su.
Put your sample in the magnet and go over to the box on the floor to the left of the magnet which has several BNC connectors on it. Make sure the Acqi window is closed before tuning.
The actual tuning channel is in the middle of the three sections. The right channel is for ¹H and ¹⁹F spectra, the left is for everything else (³¹P or ¹³C or ¹⁴N). Use the BNC cables from whichever side matches whatever type of nucleus you need to tune.
Remove the BNC cable connected to the PROBE input and connect it to the middle channel PROBE connection (which is near the buttons that say TUNE and ATTEN). Then remove the BNC cable connected to the TUNE input from the same channel and connect it to the middle channels TUNE OUTPUT connection. A red light will start blinking.
Channel 1 is denoted tn (transmitter nucleus) and Channel 2 is denoted dn (decoupler nucleus). The gray VNMR window which displays the parameters uses this convention (tn and dn).
Push the + button on the CHAN side so that the number 1 comes up on the channel side. This allows you to tune the tn (transmitter nucleus). Make sure that the ATTEN (attenuation) side is on either 8 or 9. The green oval shaped LED will be on with some number that (most likely) is not zero. On the bottom of the probe will be three cylindrical adjusters, they are labelled proton, carbon, and nitrogen. Adjust the probe of whatever nucleus you are using so that the number on the green LED reads close to 000 (000-010). Each adjuster has two controls, the rough section of the adjuster can be turned to change the tune capacitor, and one can turn the smooth section (just below the rough section) to change the match capacitor. Optimum tuning is achieved by adjusting the tune and match capacitors so that the number on the LED is minimized. First, the tune capacitor is adjusted so that a minimum LED reading is obtained. The match capacitor is then moved 1/2 - 1 turn and the LED reading is again minimized by adjusting the tune capacitor. If the LED reading is smaller after match capacitor movement than before, the match capacitor should be changed again in the same direction and the LED reading again minimized by changing the tune capacitor. If the LED reading is larger after match capacitor movement than before, the match capacitor should be turned in the opposite direction to the initial match capacitor movement and the LED reading minimized by adjusting the tune capacitor. One continues to iteratively adjust the tune and match capacitors until a global minimum is obtained.
After loading the file which contains parameters for acquiring proton decoupled ¹³C spectra, ¹³C is tuned through channel 1 using the BNC cables from the left side (¹³C, ³¹P and ¹⁴N), and the cables from the right side (¹H and ¹⁹F nuclei) are used to tune channel 2 (dn), as described above.
When you are done, change the channel switch so that it reads 0. The green LED will go off and the red light will blink. Remove the PROBE input and TUNE OUTPUT cables and reconnect them from whence they came.