Baseband Sample Rate in NI USRP Radios

Each NI™ USRP™ radio supports a set of master clock rates (MCRs) and decimation or interpolation factors.

The following Wireless Testbench™ objects enable you to set the baseband sample rate of the radio by using the SampleRate object property. These objects automatically select the master clock rate on the radio hardware based on the specified sample rate.

If necessary, to achieve the specified sample rate, the radio uses a Farrow rate converter. For details, see Farrow Rate Converter. To bypass the Farrow filter when using these objects, set the SampleRate property to a master clock rate value, or a supported decimation or interpolation factor of a master clock rate value.

The usrp System object™ also selects the master clock rate and decimation or interpolation factor on the radio hardware based on the specified baseband sample rate, but does not utilise a Farrow rate converter. You must set the SampleRate property to a master clock rate value, or a supported decimation or interpolation factor of a master clock rate value.

Supported Master Clock Rates

The analog-to-digital converter (ADC) and digital-to-analog converter (DAC) in USRP radios run at the full master clock rate, which is hardware-dependent. This table shows the master clocks rates available on supported NI USRP radios.

Radio Device	Master Clock Rate
USRP N300 USRP N310	122.88 MHz 125.00 MHz 153.60 MHz
USRP N320 USRP N321	200.00 MHz 245.76 MHz 250.00 MHz
USRP X300 USRP X310	184.32 MHz 200.00 MHz
USRP X410	245.76 MHz 250.00 MHz

Set Baseband Sample Rate

NI USRP radios can transmit and receive waveforms at a sample rate of MCR divided by a supported decimation or interpolation factor, where MCR is the master clock rate.

Radio	Supported Decimation or Interpolation Factor
USRP N300 USRP N310 USRP N320 USRP N321 USRP X410	1
	2
	3
	Even integer in the range from 4 to 256
	Multiple of 4 in the range from 256 to 512
	Multiple of 8 in the range from 512 to 1016
USRP X300 USRP X310	Integer in the range from 1 to 128
	Even integer in the range from 128 to 256
	Multiple of 4 in the range from 256 to 512
	Multiple of 8 in the range from 512 to 1016

Farrow Rate Converter

For the following Wireless Testbench objects, if MCR/SampleRate is not a supported decimation or interpolation factor, the signal passes through the Farrow rate converter.

Note

Because of hardware limitations, the Farrow rate converter can only convert sample rates that are less than MCR/2.

Resampling Transmit Waveform

When you call the transmit function with an object that uses a Farrow rate converter to achieve the sample rate specified by the SampleRate property, the object resamples the transmit waveform. The resulting waveform has an increased number of data samples.