THDB-ADA_HSMC, DAC voltage

I`m using the THDB-ADA_HSMC-Card with a DE2-115 Board.

I`m able to measure an output voltage of the DAC of -1V and 1V while

toggling the values of the ADC from 0 to (2^14)-1, and using the 1MOhm impedance-input of the oszilloscope.

When I use the 50Ohm impedance-input, I´m able to measure -300mV and 300mV. But - the shown rectangle-signal on the oszilloscope looks a lot

better, than using the 1MOhm input.

Which output impedance does the Daughter-Card have and which voltages should I be able to measure ?