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Desired Versus Actual Parameter Values

Desired Versus Actual Value in SDRu Blocks

For the SDRu Transmitter block or SDRu Receiver block, when you specify the parameter values to set the center frequency, gain, interpolation factor, and decimation factor, the block performs rudimentary checks to verify that the values are scalar and real. So long as the specified values pass those rudimentary checks, the values can be out of range for the USRP™ hardware. In this case, the hardware makes its best effort to set the specified value and reports the actual value on the block mask.

If the SDRu block is connected to USRP hardware, you can check the block mask to find the acceptable ranges for the center frequency and gain. The acceptable ranges for the interpolation factor and decimation factor are integer values as define in this tables.

  • Decimation factor for the SDRu receiver, specified as an integer from 1 to 1024 with restrictions, based on the radio you use.

    DecimationFactor Property ValueB-SeriesN2xx-SeriesN3xx-SeriesX-Series

    1

    Valid

    Not valid

    Valid

    Not valid when connected with TwinRX daughterboard

    2

    Valid

    Acceptable when you use only the int8 transport data type

    Valid

    Valid

    3

    Valid

    Not valid

    Valid

    Valid

    Odd integer from 4 to 128

    Valid

    Valid

    Not valid

    Valid

    Even integer from 4 to 128

    Valid

    Valid

    Valid

    Valid

    Even integer from 128 to 256

    Valid

    Valid

    Valid

    Valid

    Integer multiple of 4 from 256 to 512

    Valid

    Valid

    Valid

    Valid

    Integer multiple of 8 from 512 to 1024

    Not valid

    Not valid

    Valid

    Valid

    The radio uses the decimation factor when it downconverts the intermediate frequency (IF) signal to a complex baseband signal.

  • Interpolation factor for the SDRu transmitter, specified as an integer from 1 to 1024 with restrictions, based on the radio you use.

    InterpolationFactor Property ValueB-SeriesN2xx-SeriesN3xx-SeriesX-Series

    1

    Valid

    Not valid

    Valid

    Valid

    2

    Valid

    Acceptable when you use only the int8 transport data type

    Valid

    Valid

    3

    Valid

    Not valid

    Valid

    Valid

    Odd integer from 4 to 128

    Valid

    Valid

    Not valid

    Valid

    Even integer from 4 to 128

    Valid

    Valid

    Valid

    Valid

    Even integer from 128 to 256

    Valid

    Valid

    Valid

    Valid

    Integer multiple of 4 from 256 to 512

    Valid

    Valid

    Valid

    Valid

    Integer multiple of 8 from 512 to 1024

    Not valid

    Not valid

    Valid

    Not valid

    The radio uses the interpolation factor when it upconverts the complex baseband signal to an intermediate frequency (IF) signal.

Desired vs. Actual Value in the SDRu System Object

The comm.SDRuTransmitter System object™ or comm.SDRuReceiver System object properties display the specified values for center frequency, gain, interpolation factor, and decimation factor. However, due to quantization or range issues, the actual values can differ from your desired values.

For example, create a comm.SDRuReceiver System object, and then specify the center frequency.

h = comm.SDRuReciver
h.CenterFrequency = 2.43e9
Get the actual center frequency that is set at the USRP radio by using the info object function. The output r.CenterFrequency shows the actual center frequency.
r = info(h);
r.CenterFrequency
The System object sends the specified values to the USRP radio and then reads the actual values back when you use the info object function.

See Also

Blocks

Objects