nmr pulse generation

[MichaelOSB]

I would like to generate an analog pulse for NMR spectroscopy, but am having trouble controlling the analog output of my PCI-6110. I can create the waveform that I want to output, but when I try to write that waveform to the PCI analog output, it comes out somewhat distorted. Most notably, the nmr signal must end at amplitude 0, but when I read the signal output by the DAQ, it never ends on 0, even when I back-calculate to make sure that the waveform I created ends on a full half-cycle. I need to be able to control the pulse at frequencies in the range of 10k Hz with pulse lengths in tenths of milliseconds. How can I gain better control over my analog output signal so as to correct this? I have tried referencing some of the signal generation examples, but without much success. Thank you for any suggestions you might have.

[altenbach]

There are at least 3 possible point of failure:

1. The way you are using AO
2. The way you are reading the signal back
3. The way the hardware is setup.

Are all your signals properly terminated? Things are typically high impedance so you probably need some termination resistors or the voltage has nowhere to go when you turn off the pulse. Can you give more details on how everything is connected?

[MichaelOSB]

Right now, I am simply running the signal from the analog output and reading it directly back into the analog input of an NI BNC-2110 with a separate vi. When using the scope, I attach a 50 ohm terminator with a "T" at the scope in order to reduce reflection of the signal and added noise. I have attached the LabVIEW code for reference as to how I am using the AO.