NI 5441
FIR Filter Type: Raised Cosine

Alpha Values: 0.1 to 0.9

This low-pass filter is commonly used in communications applications. The passband of the raised cosine filter stops at 0.5 × (1 − α) of the IQ Rate. The stop-band of the raised cosine filter begins at 0.5 × (1 + α) of the IQ Rate. The transition-band of the raised cosine filter (in dB) follows the following formula:

where

S = 0.5×(1 − α)

f = Frequency (fraction of the IQ Rate)

Use the Raised Cosine Filter Alpha property or the NIFGEN_ATTR_OSP_FIR_FILTER_RAISED_COSINE_ALPHA attribute to set the α value.

The following diagram shows an ideal raised cosine filter response with an α of 0.5. The frequency axis is scaled as a fraction of the IQ Rate.

The MER/EVM (measurement of modulation accuracy) and stopband attenuation improve with a higher α.