To measure the transmitter power you need a an oscilloscope rated to well above the frequency you are observing (125.8 MHz in your case), and you need to know how to use it. You also need a high power attenuator, typically 30 dB. Depending on the power level that you are measuring, you night need an additional attenuator between the high power attenuator and the oscilloscope - this can be a lower power attenuator. Connect the transmitter through the attenuator(s) to the oscilloscope (set to 50 ohms!) and measure the peak-to-peak voltage. Multiply the peak-to-peak by 0.354 (to convert to RMS) and convert to power with P = E**2 / R, where R is 50 Ohms.

For example: 3.80 V P-P = 1.34 V RMS

P = 1.34**2 / 50 = 0.036 W

For a 30 dB attenuator, multiply this by 1000, so 36 W. If you have 40 dB of attenuation multiply by 10,000 so you would have 360 W.

Do you get a 13C signal at all? If yes does it grow to a certain extent. at what pulse length does it stop growing. Prepare a sample with a very large 13C signal. For example Acetone with a few percent Acetone-d6. Make sure the probe is well tuned. I know these are more questions than answers but they might point you in the right direction. Clemens

All my experience is with Varian systems but I'd follow the direction Kirk is sending you... I'd start at a low transmitter power (50) with a normal PW and with a short AT (aquisiton time) and many transients pules the system. You should set up your o'scope so you can measure and sync your pulses. Now I'd change over and create an array of the transmitter power and go up 3 dB each time until you reach max. Make sure you give each about 256 transients to see it on the screen and measure it.. then you should see the next step of the array kick in and your output should jump up predictably on your oscope following a power conversion chart. I wouldn't go crazy over a small amount being off because of inherant loss but based on what you're seeing I'd expect to see an output and it won't change (likely bad amp) as you move thru your array... if it does go up as you'd expect it would appear to be a probe issue. Good luck.