Aliasing is a situation in which the signal being sampled contains frequencies which are greater than 1/2 the sampling rate. If this is the case, the signal will be detected by the analyzer but the frequency will be incorrect. For instance, if the sampling rate is 6,000 Hz and a 3,500 Hz signal is applied to the input, the analyzer will show the signal at 2,500Hz.
Check the specifications of the specific DT-9800 hardware module to determine if the module provides built-in anti aliansing protection.
See also: Sampling Rate, Measurement Accuracy