NI 5783 Analog output

[jerardvincentang]

I am new to labview and fpga programming. I want to try and use my NI 7972 with NI 5783 adapter module to generate a 300Khz sine wave. I am currently using the getting started vi. For signals 1 MHz and above, I get the correct signal on my oscilloscope, however, for anything below 1 MHz my signal is all messed up. I am using 50 Ohm cables as recommended by NI. Anyone know why this is happening?

Here is the output when I set the frequency to 900 Mhz (square)

200kHz

for 1MHz and anything above, the signal is correct: