Tuning EMX500

From NMR Wiki

insert sample into the cavity

Note that if you are working with a liquid nitrogen dewar, make sure to turn on dry N2 gas to blow through the cavity. This insures that no air moisture is condensed on the outer walls of the dewar.

1. Tune the frequency of MW source

start microwave bridge control interface (MW button)
switch to "tune" mode
set attenuation to 30 dB
you must now get dip picture, move around frequency slider so that the dip is just to the right of the green line
adjust phase so that dip picture looks most symmetric

Note: our EPR resonator cavity has two dips - you need to select the sharper one.

2. Turn on diode detector

switch to "operate" mode
may need to adjust frequency by clicking on slider arrows a few times so that "AFC" dial is centered on the green zone
increase attenuation to 50 dB
use "Bias" slider to center "Diode" indicator on green

3. Match the cavity

Now you will need to be lowering attenuation setting while using "Iris" ↑ and ↓ buttons to keep the "Diode" indicator in the green zone.
Note: once you reach 10 dB attenuation - stop. Lower attenuation means higher microwave power. Setting attenuation below 10 dB can damage the detector.

lower attenuation by 10 (first time to 40 dB)
if "Diode" indicator moves away from center of green zone, adjust "Iris" position to re-center position of "Diode" indicator.
repeat this part until you are at 10 dB and "Diode" indicator is re-centered

4. Touch up phase of MW source

move position of "Diode" indicator to the rightmost by slightly adjusting position of the "Phase" slider (click on white space on either side of the "Phase" slider button)

When you do this the "Diode" indicator may not move to the right at all - that means that phase is already adjusted properly. But if "Diode" does move to the right of the "green", do the following: